TOYOTA AVALON 2001 Service Repair Manual
Page 1021 of 1897
- DIAGNOSTICSENGINE
DI-53
209 Author: Date:
DTC P0171 System too Lean (Fuel Trim)
DTC P0172 System too Rich (Fuel Trim)
DTC P0174 System too Lean (A/F Lean Malfunction,
Bank2)
DTC P0175 System too Rich (Bank2)
CIRCUIT DESCRIPTION
Fuel trim refers to the feedback compensation value compared to the basic injection time. 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 air-fuel ratio at its ideal
theoretical value.
The signal from the A/F sensor is approximately proportional to the existing air-fuel ratio, and ECM compar-
ing it with the ideal theoretical value, the ECM reduces fuel volume immediately if the air-fuel ratio is rich
and increases fuel volume if it is lean.
Long-term fuel trim compensates the deviation from the central value of the short-term fuel trim stored up
by each engine tolerance, and the deviation from the central value due to the passage of time and changes
of using environment.
If both the short-term fuel trim and long-term fuel trim exceed a certain value, it is detected as a malfunction
and the MIL lights up.
DTC No.DTC Detecting ConditionTrouble Area
P0171
P0174When air-fuel ratio feedback is stable after engine warming up,
fuel trim is considerably in error on rich side (2 trip detection
logic)
Air induction system
Injector blockage
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leakage on exhaust system
Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
A/F sensor (bank 1, 2 sensor 1)
ECM
P0172
P0175When air-fuel ratio feedback is stable after engine warming up,
fuel trim is considerably in error on lean side (2 trip detection
logic)
Injector leak, blockage
Mass air flow meter
Engine coolant temp. sensor
Ignition system
Fuel pressure
Gas leakage on exhaust system
Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
A/F sensor (bank 1, 2 sensor 1)
ECM
DI6T4-03
Page 1022 of 1897
DI-54
- DIAGNOSTICSENGINE
210 Author: Date:
HINT:
When the DTC P0171 or P0174 is recorded, the actual air-fuel ratio is on the lean side. When DTC
P0172 or P0175 is recorded, the actual air-fuel ratio is on the rich side.
If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 or P0174 is recorded. The MIL
then comes on.
If the total of the short-term fuel trim value and the long-term fuel trim value is within + 35 % (80°C
(176°F) or more), the system is functioning normally.
The A/F sensors (bank 1, 2 sensor 1) output voltage and the short-term fuel trim value can be read
using the OBD II scan tool or hand-held tester.
The ECM controls the voltage of AFR+, AFL+, AFR- and AFL- terminals of ECM to the fixed voltage.
Therefore, it is impossible to confirm the A/F sensor output voltage without OBD II scan tool or hand-
held tester.
OBD II scan tool (excluding hand-held tester) displays the one fifth of the A/F sensors (bank 1, 2 sen-
sor 1) output voltage which is displayed on the hand-held tester.
WIRING DIAGRAM
Refer to DTC P0125 on page DI-43.
INSPECTION PROCEDURE
HINT:
Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool. Because freeze frame records
the engine conditions when the malfunction is detected. When troubleshooting, it is useful for determining
whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean
or rich, etc. at the time of the malfunction.
1 Check air induction system (See page SF-1).
NG Repair or replace.
OK
2 Check injector injection (See page SF-23).
NG Replace injector.
OK
Page 1023 of 1897
- DIAGNOSTICSENGINE
DI-55
211 Author: Date:
3 Check mass air flow meter (See page SF-31) and engine coolant temperature
sensor (See page SF-73).
NG Repair or replace.
OK
4 Check for spark and ignition (See page IG-1).
NG Repair or replace.
OK
5 Check fuel pressure (See page SF-6).
NG Check and repair fuel pump, pressure regulator,
fuel pipe line and filter.
OK
6 Check gas leakage on exhaust system.
NG Repair or replace.
OK
Page 1024 of 1897
DI-56
- DIAGNOSTICSENGINE
212 Author: Date:
7 Check output voltage A/F sensor (bank 1, 2 sensor 1).
PREPARATION:
(a) Connect the OBDII scan tool or TOYOTA hand-held tester to the DLC3.
(b) Warm up the A/F sensor with the engine speed at 2,500 rpm for approx. 90 sec.
CHECK:
Read the voltage value of the A/F sensor on the screen of OBDII scan tool or TOYOTA hand-held tester
when you perform all the following conditions.
HINT:
The voltage of the AFR+ or AFL+ terminal of the ECM is 3.3 fixed the AFR- or AFL- terminal is 3.0 V fixed.
Therefore, it is impossible to check the A/F sensor output voltage at the terminals (AFR+, AFL+/AFR-, AFL-)
of the ECM.
OK:
ConditionA/F Sensor Voltage value
Engine idling
Engine racingNot remains at 3.30 V (0.660 V*)
Not remains at38V(076V*) or moreDriving at engine speed 1,500 rpm or more and vehicle
speed 40 km/h (25mph) or more, and operate throttle valve
open and closeNot remains at 3.8 V (0.76 V*) or more
Not remains at 2.8 V (0.56 V*) or less
*: When you use OBDII scan tool (excluding TOYOTA hand-held tester)
HINT:
During fuel enrichment, there is a case that the output voltage of the A/F sensor is below 2.8 V (0.56
V*), it is normal.
During fuel cut, there is a case that the output voltage of the A/F sensor is above 3.8 V (0.76 V*), it
is normal.
If the output voltage of the A/F sensor remains at 3.30 V (0.660 V*) even after performing all the above
conditions, the A/F sensor circuit may be open.
If the output voltage of the A/F sensor remains at 3.8 V (0.76 V*) or more, or 2.8 V (0.56 V*) or less
even after performing all the above conditions, the A/F sensor circuit may be short.
*: When you use the OBDII scan tool (excluding TOYOTA hand-held tester).
OK Go to step 9.
NG
Page 1025 of 1897
- DIAGNOSTICSENGINE
DI-57
213 Author: Date:
8 Check for open and short in harness and connector between ECM and A/F sen-
sors (bank 1, 2 sensor 1) (See page IN-30).
NG Repair or replace harness or connector.
OK
Replace A/F sensor.
9 Perform confirmation driving pattern (See page DI-106).
Go
10 Is there DTC P0171, P0172, P0174 or P0175 being output again?
YES Check and replace ECM (See page IN-30).
NO
11 Did vehicle runs out of fuel in past?
NO Check for intermittent problems
(See page DI-3).
YES
DTC P0171, P0172, P0174 or P0175 is caused
by running out of fuel.
Page 1026 of 1897
A11665
IG Switch
BatteryECM Engine Room J/B
MAIN
Park/Neutral
Position SwitchAM2
W-B
Starter
B
58
3
2
110
4
1
B-W2C 2G2A
S1E8 ST Relay
E1 STA 7 1
ED
B-R B-R
II2
W-R
W-B
4
2D
42F 2A6
3
2B2
B-R 8
7
II1
B-W
FL
MainJ1
J/C
B-R
S212C7
7
B
IF1
1F74
W-R
B-R F6Fusible
Link
Block6 512
B
B
W-B DI-142
- DIAGNOSTICSENGINE
298 Author: Date:
2001 AVALON (RM808U)
Starter Signal Circuit
CIRCUIT DESCRIPTION
When the engine is cranked, the intake air flow is slow, so fuel vaporization is poor. A rich mixture is therefore
necessary in order to achieve good startability. While the engine is being cranked, the battery positive volt-
age is applied to terminal STA of the ECM. The starter signal is mainly used to increase the fuel injection
volume for the starting injection control and after-start injection control.
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:
This diagnostic chart is based on the premise that the engine is cranked normally. If the engine is not
cranked, proceed to the problem symptoms table on page DI-22.
DI08B-09
Page 1027 of 1897
A02045
START
STA
(+) (-)
- DIAGNOSTICSENGINE
DI-143
299 Author: Date:
2001 AVALON (RM808U)
TOYOTA hand-held tester:
1 Connect TOYOTA hand-held tester, and check STA signal.
PREPARATION:
(a) Connect the TOYOTA hand-held tester to the DLC3.
(b) Turn the ignition switch ON and push the TOYOTA hand-held tester main switch ON.
CHECK:
Read the STA signal on the TOYOTA hand-held tester while the starter operates.
OK:
Ignition Switch PositionONSTART
STA SignalOFFON
OK Proceed to next circuit inspection shown on
problem symptom table (See page DI-22).
NG
2 Check for open in harness and connector between ECM and starter relay (Mark-
ing: ST) (See page IN-30).
NG Repair or replace harness or connector.
OK
Check and replace ECM (See page IN-30).
OBD II scan tool (excluding TOYOTA hand-held tester):
1 Check voltage between terminal STA of ECM connector and body ground.
PREPARATION:
Remove the glove compartment (See page SF-83).
CHECK:
Measure the voltage between terminal STA of the ECM connec-
tor and body ground during the engine cranking.
OK:
Voltage: 6 V or more
OK Proceed to next circuit inspection shown on
problem symptom table (See page DI-22).
Page 1028 of 1897
DI-144
- DIAGNOSTICSENGINE
300 Author: Date:
2001 AVALON (RM808U)
NG
2 Check for open in harness and connector between ECM and starter relay (Mark-
ing: ST) (See page IN-30).
NG Repair or replace harness or connector.
OK
Check and replace ECM (See page IN-30).
Page 1029 of 1897
DI079-04
ENGINE CONTROL SYSTEM Check Sheet
Customer's Name
Driver's Name
Date Vehicle
Brought in
License No.
Model and Model
Year
Frame No.
Engine Model
Odometer Reading
Problem Symptoms
Engine does
not Start
Difficult to
Start
Poor Idling
Poor
Driveability
Engine Stall
Others
Engine does not crankNo initial combustionNo complete combustion
Engine cranks slowly
Other
Incorrect first idleIdling rpm is abnormalHigh ( rpm)Low ( rpm)
Rough idling
Other
HesitationBack fireMuffler explosion (after-fire)Surging
Knocking
Other
Soon after startingAfter accelerator pedal depressed
After accelerator pedal released
During A/C operation
Shifting from N to D
Other
Dates Problem
Occurred
Problem Frequency
Condition When
Problem Occurs
Weather
Engine Operation
Engine Temperature Place Outdoor
TemperatureConstant
Sometimes ( times per day/month)Once only
Other
Fine
CloudyRainySnowyVarious/Other
Hot
Warm CoolCold (approx. °F/ °C)
Highway
SuburbsInner cityUphillDownhill
Rough road
Other
Cold
Warming upAfter warming upAny temperatureOther
Starting
Just after starting ( min.)IdlingRacing
Driving
Constant speedAccelerationDeceleration
A/C switch ON/OFF
Other
Condition of MILRemains on Sometimes light up Does not light up
NormalMalfunction code(s) (code )
Freezed frame data ( )
NormalMalfunction code(s) (code )
Freezed frame data ( )
Normal Mode
(Precheck)
Check Mode DTC InspectionInspector's
Name
km
miles
DI-2
- DIAGNOSTICSENGINE
158 Author: Date:
2001 AVALON (RM808U)
CUSTOMER PROBLEM ANALYSIS CHECK
Page 1030 of 1897
DI07B-20
DI-14
- DIAGNOSTICSENGINE
170 Author: Date:
DIAGNOSTIC TROUBLE CODE CHART
HINT:
Parameters listed in the chart may not be exactly the same as your reading due to the type of instrument
or other factors.
If a malfunction code is displayed during the DTC check in check mode, check the circuit for the codes listed
in the table below. For details of each code, turn to the page referred to under the ''See page '' for the respec-
tive ''DTC No.'' in the DTC chart.
SAE CONTROLLED
DTC No.
(See page)Detection ItemTrouble AreaMIL*1Memory
P0100
(DI-23)Mass Air Flow Circuit Malfunc-
tionOpen or short in mass air flow meter circuit
Mass air flow meter
ECM
P0101
(DI-27)Mass Air Flow Circuit Range/
Performance ProblemMass air flow meter
P0110
(DI-28)Intake Air Temp. Circuit Malfunc-
tionOpen or short in intake air temp. sensor circuit
Intake air temp. sensor (built into mass air flow meter)
ECM
P0115
(DI-32)Engine Coolant Temp. Circuit
MalfunctionOpen or short in engine coolant temp. sensor circuit
Engine coolant temp. sensor
ECM
P0116
(DI-36)Engine Coolant Temp. Circuit
Range/Performance ProblemCooling system
Engine coolant temp. sensor
P0120
(DI-38)Throttle/Pedal Position Sensor/
Switch ºAº Circuit MalfunctionOpen or short in throttle position sensor circuit
Throttle position sensor
ECM
P0121
(DI-42)Throttle/Pedal Position Sensor/
Switch ºAº Circuit Range/Perfor-
mance Problem
Throttle position sensor
P0125
(DI-43)Insufficient Coolant Temp. for
Closed Loop Fuel Control
Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
A/F sensor (bank 1, 2 sensor 1)
Air induction system
Fuel pressure
Injector
Gas leakage on exhaust system
ECM
P0128
(DI-48)Thermostat Malfunction
Thermostat
Cooling system
Engine coolant temp. sensor
ECM
P0136
(DI-49)Oxygen Sensor Circuit Malfunc-
tion (Bank 1 Sensor 2)Open or short in heated oxygen sensor circuit
Heated oxygen sensor
P0141
(DI-51)Oxygen Sensor Heater Circuit
Malfunction (Bank 1 Sensor 2)Open or short in heater circuit of heated oxygen sensor
Heated oxygen sensor heater
ECM