TOYOTA CAMRY 1999 Service Repair Manual

A00477
Atmosphere
Cover
Exhaust GasPlatinum
Electrode
Solid Electrolyte
(Zirconia Element)
Platinum
Electrode
Heater
Air±Fuel Ratio
(V)
2.6 4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.4
14 15 16 17 19 21 22
Coating (Ceramic)
ECM Monitored
A/F Sensor Voltage
DI±40
± DIAGNOSTICSENGINE
DTC P0125 Insufficient Coolant Temp. for Closed Loop
Fuel Control
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three±way cata-
lytic converter is used, but for the most efficient use of the three±way catalytic converter, the air±fuel ratio
must be precisely controlled so that it is always close to the stoichiometric air±fuel ratio.
The A/F sensor has the characteristic that provides output voltage
* approximately proportional to the exist-
ing air±fuel ratio. The A/F sensor output voltage
* is used to provide feedback for the ECM to control the air±
fuel ratio.
By the A/F sensor output, the ECM can determine the deviation amount from the stoichiometric air±fuel ratio
and control the proper injection time immediately. If the A/F sensor is malfunctioning, ECM is unable to per-
form accurate air±fuel ratio control.
The A/F sensor is equipped with a heater which heats the zirconia element. The heater is controlled by the
ECM. When the intake air volume is low (the temp. of the exhaust gas is low), current flows to the heater
to heat the sensor for accurate oxygen concentration detection.
*: The voltage value changes at the inside of the ECM only.
DTC No.DTC Detecting ConditionTrouble Area
P0125
After engine is warmed up, A/F sensor output* does not
change when conditions (a), (b) and (c) continue for at least
1.5 min.:
*: Output value changes at inside of ECM only
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 40 ± 100 km/h (25 ± 62 mph)
(c) Throttle valve is not fully closed
Open or short in A/F sensor (bank 1 sensor 1) circuit

A/F sensor (bank 1 sensor 1)

Air induction system

EGR system

Fuel pressure

Injector

Gas leakage on exhaust system

ECM
HINT:

After confirming DTC P0125, use the OBD II scan tool or TOYOTA hand-held tester to confirm voltage
output of A/F sensor from the CURRENT DATA.

The ECM controls the voltage of the AF+ and AF± terminals of the ECM to the fixed voltage. Therefore,
it is impossible to confirm the A/F sensor output voltage without OBD II scan tool or TOYOTA hand±
held tester.
DI1JU±04

A09395
B±Y
FL
Block47
EFI
IGN
14 2
4 EFI
Relay
21
53
B±Y
3
12 B
B
1
243 9
IG1B
W±R
P±B
G
P±B 56
2
5
1K
14
HT2 21 1W
E4E5
E6E5
MAIN FLE5 1B
B 1ECM
AF+
OX2 HTAF
AF± 1K
2F
E03 E1E04 A/F
Sensor
Engine Room R/B No.2
B±YJ18 J/C
2
1
IG3IG3
IG3
EB
EC
Instrument
Panel J/B7
3 5
6
7
2L 2A
F1111
F9
B±G
Battery B±R
2K
2J
W±B
3.3V
3.0V
AM2 B
W±R
to Analog±Digital
Converter
B±Y B±Y
IG Switch
B±R
2 E
E
J23 J/C
B
BB±YL
B±W
BR
(*1)
J23 J/C
Heated
Oxygen
Sensor
(Bank 1
Sensor 2)
B
IG17G
BR
BR
J20
J/C A
A
± DIAGNOSTICSENGINE
DI±41


OBD II scan tool (excluding TOYOTA hand±held tester) displays the one fifth of the A/F sensor output
voltage which is displayed on the TOYOTA hand±held tester.
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:

If the vehicle run out of fuel, the air±fuel ratio is LEAN and DTC P0125 will be recorded. The MIL then
comes on.

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 Are there any other codes (besides DTC P0125) being output?
YES Go to relevant DTC chart.
NO

DI±42
± DIAGNOSTICSENGINE
2 Connect OBD II scan tool or TOYOTA hand±held tester, and read value for volt-
age output of A/F sensor (bank 1 sensor 1).
PREPARATION:
(a) Connect the OBD II 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 OBD II scan tool or TOYOTA hand±held tester
when you perform all the following conditions.
HINT:
The voltage of the AF+ terminal of the ECM is 3.3 V fixed and the A/F± terminal is 3.0 V fixed. Therefore,
it is impossible to check the A/F sensor output voltage at the terminals (AF+/AF±) of the ECM.
OK:
ConditionA/F Sensor Voltage Value
Engine idling
Engine racing
Not remains at 3.30 V (0.660 V*)
Driving at engine speed 1,500 rpm or more and vehicle
speed 40 km/h (25 mph) or more, and operate throttle valve
open and close
Not remains at 3.30 V (0.660 V)

Not remains at 4.5 V (0.76 V*) or more
*: When you use the OBD II 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, A/F the sensor circuit may be open.

If the output voltage of the A/F sensor remains at 4.5 V (0.76 V*) or more, even after performing all
the above conditions, A/F sensor circuit may be short.
*: When you use the OBD II scan tool (excluding TOYOTA hand±held tester).
OK Go to step 10.
NG
3 Check for open and short in harness and connector between ECM and A/F sen-
sor (bank 1 sensor 1) (See page IN±29).
NG Repair or replace harness or connector.
OK
4 Check resistance of A/F sensor heater (bank 1 sensor 1) (See Pub. No. RM654U,
page SF±59).

± DIAGNOSTICSENGINE
DI±43
NG Replace A/F sensor.
OK
5 Check air induction system (See Pub. No. RM654U, page SF±1).
NG Replace or replace.
OK
6 Check EGR system (See Pub. No. RM654U, page EC±12).
NG Repair EGR system.
OK
7 Check fuel shutoff valve operation (See page DI±86).
NG Replace and repair.
OK
8 Check injector injection (See Pub. No. RM654U, page SF±23).
NG Replace injector.
OK
9 Check gas leakage on exhaust system.

DI±44
± DIAGNOSTICSENGINE
NG Repair or replace.
OK
Replace A/F sensor (bank 1 sensor 1).
10 Perform confirmation driving pattern (See page DI±79).
Go
11 Is there DTC P0125 being output again?
YES Check and replace ECM.
NO
12 Did vehicle runs out of fuel in past?
NO Check for intermittent problems.
YES
DTC P0125 is caused by running out of fuel.

± DIAGNOSTICSENGINE
DI±45
DTC P0136 Oxygen Sensor Circuit Malfunction (Bank 1
Sensor 2)
CIRCUIT DESCRIPTION
Refer to DTC P0125 on page DI±40.
DTC No.DTC Detecting ConditionTrouble Area
P0136
Voltage output of heated oxygen sensor remains at 1.0 V or
more, or 0.55 V or less when vehicle is driven at 40 km/h (25
mph) or more after engine is warmed up (2 trip detection logic)
Open or short in heated oxygen sensor circuit

Heated oxygen sensor
HINT:
Sensor 2 refers to the sensor farther away from the engine body.
WIRING DIAGRAM
Refer to DTC P0125 on page DI±40.
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 Are there any other codes (besides DTC P0136) being output?
YES Go to relevant DTC chart.
NO
2 Check for open and short in harness and connector between ECM and heated
oxygen sensor (See page IN±29).
NG Repair or replace harness or connector.
OK
3 Check output voltage of heated oxygen sensor.
PREPARATION:
(a) Connect the OBD II scan tool or TOYOTA hand±held tester to the DLC3.
(b) Warm up the engine to normal operating temp.
DI00Y±10

DI±46
± DIAGNOSTICSENGINE
CHECK:
Read the voltage output of the heated oxygen sensor when the engine is suddenly raced.
HINT:
Perform quick racing to 4,000 rpm 3 min. using the accelerator pedal.
OK:
Heated oxygen sensor output voltage: Alternates from 1.0 V or less to 0.55 V or more.
OK Check that each connector is properly con-
nected.
NG
Replace heated oxygen sensor.

A09296BE6653A09265
ON
HT2
(±) (+)
± DIAGNOSTICSENGINE
DI±47
DTC P0141 Oxygen Sensor Heater Circuit Malfunction
(Bank 1 Sensor 2)
CIRCUIT DESCRIPTION
Refer to DTC P0125 on page DI±40.
DTC No.DTC Detecting ConditionTrouble Area
P0141When heater operates, heater current exceeds 2 A
(2 trip detection logic)
Open or short in heater circuit of heated oxygen sensor
Htd ht
P0141Heater current of 0.2 A or less when heater operates
(2 trip detection logic)
Heated oxygen sensor heater

ECM
HINT:

Sensor 1 refers to the sensor closer to the engine body.

Sensor 2 refers to the sensor farther away from the engine body.
WIRING DIAGRAM
Refer to DTC P0125 on page DI±40.
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 voltage between terminals HT2 of ECM connector and body ground.
PREPARATION:
(a) Remove the glove compartment (See Pub. No. RM654U,
page SF±64).
(b) Turn the ignition switch ON.
CHECK:
Measure the voltage between terminals HT2 of the ECM con-
nector and body ground.
HINT:
OK:
Voltage: 9 ± 14 V
OK Check and replace ECM (See page IN±29).
NG
DI00X±05

DI±48
± DIAGNOSTICSENGINE
2 Check resistance of heated oxygen sensor heater (See Pub. No. RM654U, page
SF±63).
NG Replace heated oxygen sensor.
OK
Check and repair harness or connector between EFI main relay (Marking: EFI) and heated oxygen
sensor, and heated oxygen sensor and ECM (See page IN±29).

± DIAGNOSTICSENGINE
DI±49
DTC P0171 System too Lean (Fuel Trim)
DTC P0172 System too Rich (Fuel Trim)
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 for 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 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
When 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

Manifold absolute pressure sensor

Engine coolant temp. sensor

Fuel shutoff valve for delivery pipe

Gas leakage on exhaust system

Air induction system

Open or short in A/F sensor (bank 1 sensor 1) circuit

A/F sensor (bank 1 sensor 1)

ECM
P0172
When 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

Manifold absolute pressure sensor

Engine coolant temp. sensor

Ignition system

Fuel shutoff valve for delivery pipe

Gas leakage on exhaust system

Open or short in A/F sensor (bank 1 sensor 1) circuit

A/F sensor (bank 1 sensor 1)

ECM
HINT:

When the DTC P0171 is recorded, the actual air±fuel ratio is on the LEAN side. When DTC P0172 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 is recorded. The MIL then comes
on.

If the total of the short±term fuel trim value and long±term fuel trim value is within +38 %, the system
is functioning normally.

The A/F sensor output voltage and the short±term fuel trim value can be read using the OBD II scan
tool or TOYOTA hand±held tester.
DI1JW±04