coolant temperature sensor INFINITI FX35 2005 Service Manual

CO-28
[VQ35DE]
WATER OUTLET AND WATER PIPING
Revision: 2005 July 2005 FX
WATER OUTLET AND WATER PIPINGPFP:11060
ComponentsABS00E82
Removal and InstallationABS007ZU
REMOVAL
1. Remove front engine undercover with power tool.
2. Drain engine coolant from radiator drain plug at the bottom of radiator, and from water drain plug at the front of cylinder block. Refer to CO-11, "
Changing Engine Coolant" and CO-22, "WATER PUMP" .
CAUTION:

Perform this step when the engine is cold.

Do not spill engine coolant on drive belts.
3. Remove engine cover with power tool. Refer to EM-19, "
INTAKE MANIFOLD COLLECTOR" .
4. Remove air duct (inlet), air duct and air cleaner case assembly. Refer to EM-17, "
AIR CLEANER AND AIR
DUCT" .
5. Remove radiator hose (upper) and heater hose.
6. Remove the following parts, when remove water outlet.

A/T fluid charging pipe; Refer to AT- 2 7 0 , "TRANSMISSION ASSEMBLY" .

Intake manifold collectors (upper and lower). Refer to EM-19, "INTAKE MANIFOLD COLLECTOR" .

Rocker cover (right bank). Refer to EM-51, "ROCKER COVER" .
7. Remove engine coolant temperature sensor as necessary. CAUTION:
Be careful not to damage engine coolant temperature sensor.
8. Remove water outlet, heater pipe, water bypass hoses and water pipe.
1. Harness bracket 2. Water hose 3. Water bypass hose
4. Engine coolant temperature sensor 5. Gasket 6. Water outlet
7. Heater hose 8. Water pipe 9. Radiator hose (upper)
10. Heater pipe 11. Washer 12. O-ring
SBIA0484E

DI-1
DRIVER INFORMATION SYSTEM
K ELECTRICAL
CONTENTS
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DRIVER INFORMATION SYSTEM
PRECAUTION ............................................................ 4
Precautions for Supplemental Restraint System
(SRS) “AIR BAG” and “SEAT BELT PRE-TEN-
SIONER” ............................................................. ..... 4
COMBINATION METERS ...................................... ..... 5
System Description ............................................. ..... 5
UNIFIED METER CONTROL UNIT ................. ..... 5
UNIFIED METER AND A/C AMP. .................... ..... 5
HOW TO CHANGE THE DISPLAY FOR ODO/
TRIP METER ................................................... ..... 6
POWER SUPPLY AND GROUND CIRCUIT ... ..... 6
SPEEDOMETER .............................................. ..... 7
TACHOMETER ................................................ ..... 7
WATER TEMPERATURE GAUGE ................... ..... 7
FUEL GAUGE .................................................. ..... 7
Component Parts and Harness Connector Location ..... 7
Arrangement of Combination Meter .................... ..... 8
Circuit Diagram ................................................... ..... 9
Wiring Diagram — METER — ............................. ... 10
Terminals and Reference Value for Combination
Meter ................................................................... ... 12
Terminals and Reference Value for Unified Meter
and A/C Amp. ...................................................... ... 13
Self-Diagnosis Mode of Combination Meter ........ ... 14
SELF-DIAGNOSIS FUNCTION ....................... ... 14
OPERATION PROCEDURE ............................ ... 14
CONSULT-II Function (METER A/C AMP) .......... ... 14
Trouble Diagnosis ............................................... ... 15
HOW TO PERFORM TROUBLE DIAGNOSIS ... 15
PRELIMINARY CHECK ................................... ... 15
Symptom Chart 1 ................................................ ... 17
Symptom Chart 2 ................................................ ... 17
Power Supply and Ground Circuit Inspection ..... ... 18
Vehicle Speed Signal Inspection ......................... ... 20
Engine Speed Signal Inspection ......................... ... 21
Engine Coolant Temperature Signal Inspection .. ... 21
Fuel Level Sensor Signal Inspection ................... ... 22
Odo/Trip Meter and Illumination Control Switch
Inspection ............................................................ ... 24
Fuel Gauge Pointer Fluctuates, Indicator Wrong Value or Varies ....................................................
... 24
Fuel Gauge Does Not Move to FULL Position .... ... 24
Electrical Components Inspection ....................... ... 25
CHECK FUEL LEVEL SENSOR UNIT ............. ... 25
Removal and Installation of Combination Meter .. ... 25
Disassembly and Assembly of Combination Meter ... 26
DISASSEMBLY ................................................ ... 26
ASSEMBLY ...................................................... ... 27
Removal and Installation of Odo/Trip Meter and Illu-
mination Control Switch ....................................... ... 27
REMOVAL ........................................................ ... 27
INSTALLATION ................................................ ... 27
UNIFIED METER AND A/C AMP ........................... ... 28
System Description .............................................. ... 28
INPUT/OUTPUT SIGNALS .............................. ... 28
FAIL-SAFE ....................................................... ... 29
CAN Communication System Description ........... ... 29
CAN Communication Unit .................................... ... 29
Schematic ............................................................ ... 30
CONSULT-II Function (METER A/C AMP) .......... ... 31
CONSULT-II BASIC OPERATION .................... ... 31
SELF-DIAGNOSTIC RESULTS ........................ ... 32
DATA MONITOR .............................................. ... 32
DTC [U1000] CAN Communication Circuit .......... ... 34
DTC [B2202] Meter Communication Circuit ........ ... 34
DTC [B2205] Vehicle Speed Circuit ..................... ... 37
Removal and Installation of Unified Meter and A/C
Amp. .................................................................... ... 37
REMOVAL ........................................................ ... 37
INSTALLATION ................................................ ... 37
COMPASS .............................................................. ... 38
System Description .............................................. ... 38
DIRECTION DISPLAY ...................................... ... 38
Wiring Diagram – COMPAS – ............................. ... 40
Removal and Installation of Compass ................. ... 41
WARNING LAMPS ................................................. ... 42
Schematic ............................................................ ... 42
Wiring Diagram — WARN — ............................... ... 43
Oil Pressure Warning Lamp Stays Off (Ignition
Switch ON) .......................................................... ... 51

COMBINATION METERS DI-7
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SPEEDOMETER
ABS actuator and electric unit (control unit) provides a vehicle speed signal to the unified meter and A/C amp.
with CAN communication line. After unified meter and A/C amp. received the vehicle speed signal, it changes
the signal to 8 pulse signal and provides the 8 pulse signal to the combination meter for the speedometer.
TACHOMETER
The tachometer indicates engine speed in revolutions per minute (rpm).
ECM provides an engine speed signal to unified meter and A/C amp. with CAN communication line. Unified
meter and A/C amp. provides an engine speed signal to combination meter for tachometer with communica-
tion line between unified meter and A/C amp. and combination meter.
WATER TEMPERATURE GAUGE
The water temperature gauge indicates the engine coolant temperature.
ECM provides an engine coolant temperature signal to unified meter and A/C amp. with CAN communication
line. Unified meter and A/C amp. provides a engine coolant temperature signal to combination meter for water
temperature gauge with communication line between unified meter and A/C amp. and combination meter.
FUEL GAUGE
The fuel gauge indicates the approximate fuel level in the fuel tank.
The fuel gauge is regulated by a variable ground signal supplied

from unified meter and A/C amp. terminal 36

through the fuel level sensor unit and fuel pump (main) terminals 5 and 2, and

through the fuel level sensor unit (sub) terminals 2 and 1

to unified meter and A/C amp. terminal 28 for the fuel gauge.
Unified meter and A/C amp. provides a fuel level signal to combination meter for fuel gauge with communica-
tion line between unified meter and A/C amp. and combination meter.
Component Parts and Harness Connector LocationAKS005MI
PKIB1955E

COMBINATION METERS DI-17
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Symptom Chart 1 AKS005MT
Symptom Chart 2AKS005MU
Trouble phenomenon Possible cause
Indication is irregular for the speedometer and odo/trip meter. Refer to DI-20, "
Vehicle Speed Signal Inspection" .
Tachometer indication is malfunction. Refer to DI-21, "
Engine Speed Signal Inspection" .
Water temperature gauge indication is malfunction. Refer to DI-21, "
Engine Coolant Temperature Signal Inspection" .
Fuel gauge indication is malfunction. Refer to DI-22, "
Fuel Level Sensor Signal Inspection" .
Low-fuel warning lamp indication is irregular.
A/T position indicator is malfunction. Refer to DI-56, "
A/T Indicator Is Malfunction" .
Illumination control does not operate. Refer to
DI-24, "
Odo/Trip Meter and Illumination Control Switch
Inspection" .
Displayed item [Code] Inspection contents Possible cause
CAN COMM CIRC [U1000] Inspect the CAN communication. Refer to
DI-34, "
DTC [U1000] CAN Communication Circuit" .
CAUTION:
Even when there is no malfunction on CAN communica-
tion system, malfunction may be misinterpreted when bat-
tery has low voltage (when maintaining 7 - 8 V for about 2
seconds) or 10A fuse [No. 19, located in the fuse block (J/
B)] is disconnected.
METER COMM CIRC [B2202] Inspect the communication line
between combination meter and
unified meter and A/C amp. Refer to
DI-34, "
DTC [B2202] Meter Communication Circuit" .
VEHICLE SPEED CIRC [B2205] Inspect the vehicle speed input
signal. Refer to
DI-37, "
DTC [B2205] Vehicle Speed Circuit" .
CAUTION:
Even when there is no malfunction on speed signal sys-
tem, malfunction may be misinterpreted when battery has
low voltage (when maintaining 7 - 8 V for about 2 seconds).

DI-28
UNIFIED METER AND A/C AMP
Revision: 2005 July 2005 FX
UNIFIED METER AND A/C AMPPFP:27760
System DescriptionAKS005N8

For the unified meter and A/C amp., the signal required for controlling the combination meter are inte-
grated in the A/C auto amp.

Unified meter and A/C amp. controls each operation for A/C auto amp. For information regarding A/C con-
trol, refer to AT C - 3 0 , "
AIR CONDITIONER CONTROL" in ATC section.

Unified meter and A/C amp. inputs necessary information for combination meter from each unit by CAN
communication and so on.

And unified meter and A/C amp. outputs these signals using communication line (TX, RX) between unified
meter and A/C amp. and combination meter.

The signals required for the distance to empty (DTE) display are centralized in the unified meter and A/C
amp., converted into data, and sent to the display unit (without NAVI) display control unit (with NAVI) using
CAN communication.

Other input signals are also sent to the ECM, TCM, AWD control unit, BCM, display unit (without NAVI)
and display control unit (with NAVI) using CAN communication.

The unified meter and A/C amp. correspond a CONSULT-II function (self-diagnostic results, CAN diag-
nostic support monitor, data monitor).
INPUT/OUTPUT SIGNALS
Between Unified Meter & A/C amp. and Combination Meter
Unit Input Output
Unified meter and A/C amp.

Seat belt buckle switch signal (Driver's side)

Parking brake signal

Illumination control nighttime required signal

Refuel status signal

Low-fuel warning lamp condition signal

Combination meter receive error signal

Delivery destination data signal

Combination meter specifications signal

Vehicle speed signal (8-pulse)

Engine speed signal

Engine coolant temperature signal

Fuel level sensor signal (resistance value)

Malfunction indicator lamp signal

ABS warning lamp signal

Low tire pressure warning lamp signal

Brake warning lamp signal

A/T CHECK warning lamp signal

ICC warning lamp signal

Oil pressure switch signal

Door switch signal

AWD warning lamp signal

VDC OFF indicator lamp signal

SLIP indicator lamp signal

CRUISE indicator lamp signal

SET indicator lamp signal

High beam request signal

Turn indicator signal

Snow mode switch signal

ICC system display signal

A/T position indicator signal

Manual mode indicator signal

Manual mode gear position signal

CAN communication condition signal of A/T

Position lights request signal

Buzzer output signal

EC-7
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Revision: 2005 July 2005 FX
Wiring Diagram ...................................................
. 615
Diagnostic Procedure .......................................... . 616
Component Inspection ........................................ . 618
DTC P2122, P2123 APP SENSOR ....................... . 619
Component Description ....................................... . 619
CONSULT-II Reference Value in Data Monitor Mode . 619
On Board Diagnosis Logic .................................. . 619
DTC Confirmation Procedure .............................. . 620
Wiring Diagram ................................................... . 621
Diagnostic Procedure .......................................... . 622
Component Inspection ........................................ . 624
Removal and Installation ..................................... . 625
DTC P2127, P2128 APP SENSOR ....................... . 626
Component Description ....................................... . 626
CONSULT-II Reference Value in Data Monitor Mode . 626
On Board Diagnosis Logic .................................. . 626
DTC Confirmation Procedure .............................. . 627
Wiring Diagram ................................................... . 628
Diagnostic Procedure .......................................... . 629
Component Inspection ........................................ . 632
Removal and Installation ..................................... . 632
DTC P2135 TP SENSOR ....................................... . 633
Component Description ....................................... . 633
CONSULT-II Reference Value in Data Monitor Mode . 633
On Board Diagnosis Logic .................................. . 633
DTC Confirmation Procedure .............................. . 634
Wiring Diagram ................................................... . 635
Diagnostic Procedure .......................................... . 636
Component Inspection ........................................ . 639
Removal and Installation ..................................... . 639
DTC P2138 APP SENSOR .................................... . 640
Component Description ....................................... . 640
CONSULT-II Reference Value in Data Monitor Mode . 640
On Board Diagnosis Logic .................................. . 640
DTC Confirmation Procedure .............................. . 641
Wiring Diagram ................................................... . 642
Diagnostic Procedure .......................................... . 643
Component Inspection ........................................ . 647
Removal and Installation ..................................... . 647
IGNITION SIGNAL ................................................. . 648
Component Description ....................................... . 648
Wiring Diagram ................................................... . 649
Diagnostic Procedure .......................................... . 654
Component Inspection ........................................ . 659
Removal and Installation ..................................... . 660
INJECTOR CIRCUIT .............................................. . 661
Component Description ....................................... . 661
CONSULT-II Reference Value in Data Monitor Mode . 661
Wiring Diagram ................................................... . 662
Diagnostic Procedure .......................................... . 663
Component Inspection ........................................ . 667
Removal and Installation ..................................... . 667
FUEL PUMP CIRCUIT ........................................... . 668
Description .......................................................... . 668 CONSULT-II Reference Value in Data Monitor Mode
.668
Wiring Diagram .................................................... .669
Diagnostic Procedure .......................................... .670
Component Inspection ......................................... .672
Removal and Installation ..................................... .673
REFRIGERANT PRESSURE SENSOR ................. .674
Component Description ....................................... .674
Wiring Diagram .................................................... .675
Diagnostic Procedure .......................................... .676
Removal and Installation ..................................... .678
ELECTRICAL LOAD SIGNAL ............................... .679
Description ........................................................... .679
CONSULT-II Reference Value in Data Monitor Mode .679
Diagnostic Procedure .......................................... .679
ICC BRAKE SWITCH ............................................ .680
Component Description ....................................... .680
CONSULT-II Reference Value in Data Monitor Mode .680
Wiring Diagram .................................................... .681
Diagnostic Procedure .......................................... .682
Component Inspection ......................................... .687
ASCD BRAKE SWITCH ........................................ .688
Component Description ....................................... .688
CONSULT-II Reference Value in Data Monitor Mode .688
Wiring Diagram .................................................... .689
Diagnostic Procedure .......................................... .690
Component Inspection ......................................... .694
ASCD INDICATOR ................................................. .695
Component Description ....................................... .695
CONSULT-II Reference Value in Data Monitor Mode .695
Wiring Diagram .................................................... .696
Diagnostic Procedure .......................................... .697
SNOW MODE SWITCH ......................................... .698
Description ........................................................... .698
CONSULT-II Reference Value in the Data Monitor
Mode .................................................................... .698
Wiring Diagram .................................................... .699
Diagnostic Procedure .......................................... .700
Component Inspection ......................................... .702
MIL AND DATA LINK CONNECTOR ..................... .703
Wiring Diagram .................................................... .703
SERVICE DATA AND SPECIFICATIONS (SDS) ... .705
Fuel Pressure ...................................................... .705
Idle Speed and Ignition Timing ............................ .705
Calculated Load Value ......................................... .705
Mass Air Flow Sensor .......................................... .705
Intake Air Temperature Sensor ............................ .705
Engine Coolant Temperature Sensor .................. .705
Air Fuel Ratio (A/F) Sensor 1 Heater ................... .705
Heated Oxygen sensor 2 Heater ......................... .705
Crankshaft Position Sensor (POS) ...................... .705
Camshaft Position Sensor (PHASE) ................... .705
Throttle Control Motor .......................................... .705
Injector ................................................................. .706
Fuel Pump ........................................................... .706

EC-14Revision: 2005 July 2005 FX
Diagnostic Procedure ..........................................
1305
Component Inspection ......................................... 1307
Removal and Installation ..................................... 1308
DTC P2127, P2128 APP SENSOR ........................ 1309
Component Description ....................................... 1309
CONSULT-II Reference Value in Data Monitor Mode 1309
On Board Diagnosis Logic ................................... 1309
DTC Confirmation Procedure .............................. 1310
Wiring Diagram .................................................... 1311
Diagnostic Procedure .......................................... 1312
Component Inspection ......................................... 1315
Removal and Installation ..................................... 1315
DTC P2135 TP SENSOR ....................................... 1316
Component Description ....................................... 1316
CONSULT-II Reference Value in Data Monitor Mode 1316
On Board Diagnosis Logic ................................... 1316
DTC Confirmation Procedure .............................. 1317
Wiring Diagram .................................................... 1318
Diagnostic Procedure .......................................... 1319
Component Inspection ......................................... 1322
Removal and Installation ..................................... 1322
DTC P2138 APP SENSOR .................................... 1323
Component Description ....................................... 1323
CONSULT-II Reference Value in Data Monitor Mode 1323
On Board Diagnosis Logic ................................... 1323
DTC Confirmation Procedure .............................. 1324
Wiring Diagram .................................................... 1325
Diagnostic Procedure .......................................... 1326
Component Inspection ......................................... 1330
Removal and Installation ..................................... 1330
VARIABLE INDUCTION AIR CONTROL SYSTEM
(VIAS) ..................................................................... 1331
Description ........................................................... 1331
CONSULT-II Reference Value in Data Monitor Mode 1332
Wiring Diagram .................................................... 1333
Diagnostic Procedure .......................................... 1334
Component Inspection ......................................... 1337
Removal and Installation ..................................... 1338
IGNITION SIGNAL ................................................. 1339
Component Description ....................................... 1339
Wiring Diagram .................................................... 1340
Diagnostic Procedure .......................................... 1345
Component Inspection ......................................... 1349
Removal and Installation ..................................... 1350
INJECTOR CIRCUIT .............................................. 1351
Component Description ....................................... 1351
CONSULT-II Reference Value in Data Monitor Mode 1351
Wiring Diagram .................................................... 1352
Diagnostic Procedure .......................................... 1353
Component Inspection ......................................... 1357
Removal and Installation ..................................... 1357
FUEL PUMP CIRCUIT ........................................... 1358
Description ........................................................... 1358
CONSULT-II Reference Value in Data Monitor Mode 1358
Wiring Diagram .................................................... 1359
Diagnostic Procedure ........................................... 1360
Component Inspection ......................................... 1363
Removal and Installation ...................................... 1363
REFRIGERANT PRESSURE SENSOR ................. 1364
Component Description ....................................... 1364
Wiring Diagram .................................................... 1365
Diagnostic Procedure ........................................... 1366
Removal and Installation ...................................... 1368
ELECTRICAL LOAD SIGNAL ............................... 1369
Description ........................................................... 1369
CONSULT-II Reference Value in Data Monitor Mode 1369
Diagnostic Procedure ........................................... 1369
ICC BRAKE SWITCH ............................................. 1370
Component Description ....................................... 1370
CONSULT-II Reference Value in Data Monitor Mode 1370
Wiring Diagram .................................................... 1371
Diagnostic Procedure ........................................... 1372
Component Inspection ......................................... 1377
ASCD BRAKE SWITCH ......................................... 1378
Component Description ....................................... 1378
CONSULT-II Reference Value in Data Monitor Mode 1378
Wiring Diagram .................................................... 1379
Diagnostic Procedure ........................................... 1380
Component Inspection ......................................... 1384
ASCD INDICATOR ................................................. 1385
Component Description ....................................... 1385
CONSULT-II Reference Value in Data Monitor Mode
1385
Wiring Diagram .................................................... 1386
Diagnostic Procedure ........................................... 1387
SNOW MODE SWITCH .......................................... 1388
Description ........................................................... 1388
CONSULT-II Reference Value in the Data Monitor
Mode .................................................................... 1388
Wiring Diagram .................................................... 1389
Diagnostic Procedure ........................................... 1390
Component Inspection ......................................... 1392
MIL AND DATA LINK CONNECTOR ..................... 1393
Wiring Diagram .................................................... 1393
SERVICE DATA AND SPECIFICATIONS (SDS) ... 1395
Fuel Pressure ....................................................... 1395
Idle Speed and Ignition Timing ............................. 1395
Calculated Load Value ......................................... 1395
Mass Air Flow Sensor .......................................... 1395
Intake Air Temperature Sensor ............................ 1395
Engine Coolant Temperature Sensor ................... 1395
Fuel Tank Temperature Sensor ............................ 1395
Crankshaft Position Sensor (POS) ...................... 1395
Camshaft Position Sensor (PHASE) .................... 1395
Heated Oxygen Sensor 1 Heater ......................... 1395
Heated Oxygen sensor 2 Heater ......................... 1396
Throttle Control Motor .......................................... 1396
Injector ................................................................. 1396
Fuel Pump ............................................................ 1396

PREPARATION EC-29
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Commercial Service ToolsABS006K3
Tool name
(Kent-Moore No.) Description
Leak detector
i.e.: (J-41416) Locating EVAP leak
EVAP service port
adapter
i.e.: (J-41413-OBD) Applying positive pressure through EVAP service
port
Fuel filler cap adapter
i.e.: (MLR-8382) Checking fuel tank vacuum relief valve opening
pressure
Socket wrench Removing and installing engine coolant temperature sensor
Oxygen sensor thread
cleaner
i.e.: (J-43897-18)
(J-43897-12) Reconditioning the exhaust system threads
before installing a new oxygen sensor. Use with
anti-seize lubricant shown below.
a: 18 mm diameter with pitch 1.5 mm for
Zirconia Oxygen Sensor
b: 12 mm diameter with pitch 1.25 mm for
Titania Oxygen Sensor
Anti-seize lubricant
i.e.: (Permatex
TM
133AR or equivalent
meeting MIL
specification MIL-A-
907) Lubricating oxygen sensor thread cleaning tool
when reconditioning exhaust system threads.
S-NT703
S-NT704
S-NT815
S-NT705
AEM488
S-NT779

ENGINE CONTROL SYSTEM EC-31
[VQ35DE]
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Multiport Fuel Injection (MFI) SystemABS006K7
INPUT/OUTPUT SIGNAL CHART
*1: This sensor is not used to control the engine system under normal conditions.
*2: This signal is sent to the ECM through CAN communication line.
*3: ECM determines the start signal status by the signals of engine speed and battery voltage.
SYSTEM DESCRIPTION
The amount of fuel injected from the fuel injector is determined by the ECM. The ECM controls the length of
time the valve remains open (injection pulse duration). The amount of fuel injected is a program value in the
ECM memory. The program value is preset by engine operating conditions. These conditions are determined
by input signals (for engine speed and intake air) from both the crankshaft position sensor and the mass air
flow sensor.
VARIOUS FUEL INJECTION INCREASE/DECREASE COMPENSATION
In addition, the amount of fuel injected is compensated to improve engine performance under various operat-
ing conditions as listed below.
<Fuel increase>

During warm-up

When starting the engine

During acceleration

Hot-engine operation

When selector lever is changed from N to D

High-load, high-speed operation
<Fuel decrease>

During deceleration

During high engine speed operation
Sensor Input Signal to ECM ECM function Actuator
Crankshaft position sensor (POS) Engine speed*
3
Piston position
Fuel injection
& mixture ratio
control Fuel injector
Camshaft position sensor (PHASE)
Mass air flow sensor Amount of intake air
Engine coolant temperature sensor Engine coolant temperature
Air fuel ratio (A/F) sensor 1 Density of oxygen in exhaust gas
Throttle position sensor Throttle position
Accelerator pedal position sensor Accelerator pedal position
Park/neutral position (PNP) switch Gear position
Knock sensor Engine knocking condition
Battery Battery voltage*
3
Power steering pressure sensor Power steering operation
Heated oxygen sensor 2*
1Density of oxygen in exhaust gas
Air conditioner switch*
2Air conditioner operation
Wheel sensor*
2Vehicle speed

EC-32
[VQ35DE]
ENGINE CONTROL SYSTEM
Revision: 2005 July 2005 FX
MIXTURE RATIO FEEDBACK CONTROL (CLOSED LOOP CONTROL)
The mixture ratio feedback system provides the best air-fuel mixture ratio for driveability and emission control.
The three way catalyst 1 can then better reduce CO, HC and NOx emissions. This system uses air fuel ratio
(A/F) sensor 1 in the exhaust manifold to monitor whether the engine operation is rich or lean. The ECM
adjusts the injection pulse width according to the sensor voltage signal. For more information about air fuel
ratio (A/F) sensor 1, refer to EC-488
. This maintains the mixture ratio within the range of stoichiometric (ideal
air-fuel mixture).
This stage is referred to as the closed loop control condition.
Heated oxygen sensor 2 is located downstream of the three way catalyst 1. Even if the switching characteris-
tics of air fuel ratio (A/F) sensor 1 shift, the air-fuel ratio is controlled to stoichiometric by the signal from
heated oxygen sensor 2.
Open Loop Control
The open loop system condition refers to when the ECM detects any of the following conditions. Feedback
control stops in order to maintain stabilized fuel combustion.

Deceleration and acceleration

High-load, high-speed operation

Malfunction of air fuel ratio (A/F) sensor 1 or its circuit

Insufficient activation of air fuel ratio (A/F) sensor 1 at low engine coolant temperature

High engine coolant temperature

During warm-up

After shifting from N to D

When starting the engine
MIXTURE RATIO SELF-LEARNING CONTROL
The mixture ratio feedback control system monitors the mixture ratio signal transmitted from air fuel ratio (A/F)
sensor 1. This feedback signal is then sent to the ECM. The ECM controls the basic mixture ratio as close to
the theoretical mixture ratio as possible. However, the basic mixture ratio is not necessarily controlled as orig-
inally designed. Both manufacturing differences (i.e., mass air flow sensor hot wire) and characteristic
changes during operation (i.e., injector clogging) directly affect mixture ratio.
Accordingly, the difference between the basic and theoretical mixture ratios is monitored in this system. This is
then computed in terms of “injection pulse duration” to automatically compensate for the difference between
the two ratios.
“Fuel trim” refers to the feedback compensation value compared against the basic injection duration. Fuel trim
includes short term fuel trim and long term fuel trim.
“Short term fuel trim” is the short-term fuel compensation used to maintain the mixture ratio at its theoretical
value. The signal from air fuel ratio (A/F) sensor 1 indicates whether the mixture ratio is RICH or LEAN com-
pared to the theoretical value. The signal then triggers a reduction in fuel volume if the mixture ratio is rich, and
an increase in fuel volume if it is lean.
“Long term fuel trim” is overall fuel compensation carried out long-term to compensate for continual deviation
of the short term fuel trim from the central value. Such deviation will occur due to individual engine differences,
wear over time and changes in the usage environment.
SEF503YB