2000 TOYOTA CAMRY O2 sensor

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
12 13 14 15 16 17 18
Coating (Ceramic)
ECM Monitored
A/F Sensor Voltage
19
± DIAGNOSTICSENGINE (5S±FE)
DI±55
290 Author: Date:
DTC P0125 Insufficient Coolant Temp. for Closed Loop
Fuel Control (Only for California Spec.)
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three±way
catalytic 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
Fuel system

Injector

Ignition system

Gas leakage on exhaust system

Open or short in A/F sensor circuit

A/F sensor

ECM
DI1JU±03

A03597
B±Y
FL
Block47
EFI
IGN
14 2
4 EFI
Relay
21
53
B±Y
BR
3
12 B
B
1
24 3 9
II3
J/CB
W±R
P±B
W
BG
P±B 56
2
5
1K
14
HT2 21 O 1W
E9E8
E9 E8
MAIN FLE8 1B
B 1ECMAF

OX2 HTAF
AF 1K
2F
E03 E1E04 A/F
Sensor
Engine Room R/B No.2
B±YJ19 J/C
2
1
II2II3
II3
EB
Heated
Oxygen
Sensor
(Bank 1
Sensor 2)
EC
Instrument
Panel J/B7
3 5
6
7
2L 2A
F611
F4
B±G
Battery B±R
2K
2J
W±B
3.3V
3.0V
AM2 B
W±R
J27
*1: w/o Immobiliser
*2: w/ Immobiliser
(*1)
(*2)
to Analog±Digital
Converter
E914 E8 13
(*1) (*2) J27
B±Y
B±Y
IG Switch
B±R
*3: California
(*6) (*3) (*6) (*3)
(*1)
2
MREL
E107
(*2)
EE
J27 J27
J/C
B BB±Y
II4
6
B±W(*2)
B±W(*2)
*5:TMC Made
*6:TMMK Made
L(*5)
(*3)
B±W(*5)
(*3)
BR
*4: Except California
DI±56
± DIAGNOSTICSENGINE (5S±FE)
291 Author: Date:
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 AF
and AF 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 TOYOTA hand±held
tester.

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 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 warmed up or not, the air±fuel
ratio lean or rich, etc. at the time of the malfunction.

± DIAGNOSTICSENGINE (5S±FE)
DI±57
292 Author: Date:
1 Are there any other codes (besides DTC P0125) being output?
YES Go to relevant DTC chart.
NO
2 Connect OBD II scan tool or TOYOTA hand±held tester, and read value for volt-
age output of A/F sensor.
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 at 2,500 rpm for approx. 90 sec.
CHECK:
Read 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 AF
terminal of ECM is 3.3 V fixed and the A/F terminal is 3.0 V fixed. Therefore, it is impos-
sible to check the A/F sensor output voltage at the terminals (AF
/AF) of ECM.
OK:
ConditionA/F Sensor Voltage Value
Engine idling
Engine racing
Not remains at 3.30 V (* 0.660 V)

Not remains at38V(*076V)ormoreDriving 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 3.8 V (* 0.76 V) or more

Not remains at 2.8 V (* 0.56 V) or less
*: 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 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 output voltage of 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, 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

DI±58
± DIAGNOSTICSENGINE (5S±FE)
293 Author: Date:
3 Check for open and short in harness and connector between ECM and A/F sen-
sor (See page IN±31).
NG Repair or replace harness or connector.
OK
4 Check resistance of A/F sensor heater (See page SF±59).
NG Replace A/F sensor.
OK
5 Check air induction system (See page SF±1).
NG Replace or replace.
OK
6 Check EGR system (See page EC±12).
NG Repair EGR system.
OK
7 Check fuel pressure (See page SF±6).
NG Check and repair fuel pump, fuel pipe line and
filter (See page SF±1).
OK

± DIAGNOSTICSENGINE (5S±FE)
DI±59
294 Author: Date:
8 Check injector injection (See page SF±23).
NG Replace injector.
OK
9 Check gas leakage on exhaust system.
NG Repair or replace.
OK
Replace A/F sensor.
10 Perform confirmation driving pattern (See page DI±152).
Go
11 Is there DTC P0125 being output again?
YES Check and replace ECM.
NO

P21242 FI7210
A00027
Atmosphere
Flange
Platinum Electrode
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)
Exhaust GasCoverIdeal Air±Fuel Mixture
Output Voltage
Richer ± Air Fuel Ratio ± Leaner
± DIAGNOSTICSENGINE (5S±FE)
DI±61
296 Author: Date:
DTC P0125 Insufficient Coolant Temp. for Closed Loop
Fuel Control (Except California Spec.)
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three±way
catalytic 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 heated oxygen sensor has the characteristic where by its output voltage changes suddenly in the vicinity
of the stoichiometric air±fuel ratio. This is used to detect the oxygen concentration in the exhaust gas and
provide feedback to the computer for control of the air±fuel ratio.
When the air±fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the heated
oxygen sensor informs the ECM of the LEAN condition (small electromotive force: 0 V).
When the air±fuel ratio is RICHER than the stoichiometric air±fuel ratio the oxygen concentration in the ex-
haust gas is reduced and the heated oxygen sensor informs the ECM of the RICH condition (large electromo-
tive force: 1 V).
The ECM judges by the electromotive force from the heated oxygen sensor whether the air±fuel ratio is RICH
or LEAN and controls the injection time accordingly. However, if malfunction of the heated oxygen sensor
causes output of abnormal electromotive force, the ECM is unable to perform accurate air±fuel ratio control.
The heated oxygen sensors include a heater which heats the zirconia element. The heater is controlled by
the ECM. When the intake air volume is low (the temperature of the exhaust gas is low) current flows to the
heater to heat the sensor for accurate oxygen concentration detection.
DTC No.DTC Detecting ConditionTrouble Area
P0125
After engine is warmed up, heated oxygen sensor (bank 1
sensor 1) output does not indicate RICH even once when
conditions (a), (b) and (c) continue for at least 1.5 min.:
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 40 ~ 100 km/h (25 ~ 62 mph)
(c) Throttle valve does not fully closed

Fuel system

Injector

Ignition system

Gas leakage on exhaust system

Open or short in heated oxygen sensor (bank 1 sensor 1)
circuit

Heated oxygen sensor (bank 1 sensor 1)

ECM
DI00T±05

A03596
B±Y
Engine Room R/B No.2
Battery
IG Switch17
EFI
W±R7 7 2
5 EFI
Relay
5 3
24
W±BP±B
BR14 2314 2
3
9
II3
B±Y
B±Y
W±R B
W B±Y
B
BR6
128
25 1 2K
21 1KE8
E9
AM2
E8
E9ECM
OX1
OX2 HT1
HT2 1K 2JB±Y
J/C
1B
2F5 B±R
1W
Heated
Oxygen
Sensor
(Bank 1
Sensor 1)
II2
II3Heated
Oxygen
Sensor
(Bank 1
Sensor 2)E03
B J19 J/C
BBB
3
MAIN 2A 2L 4
F4 F6FL
Block
B±GP±B
J27 J27
1
EB
EC
6
IGN
E03 L±YE1
E1 Instrument
Panel J/B
11
B±R
*1: w/o Immobiliser
*2: w/ Immobiliser
(*2) (*1)
E9 14E8 E9 E85
1
13
(*2) (*1)(*1) (*2)(*1) (*2) (*3)
EB±Y
(*3) (*3)
(*1)FL
*3: Except California BII3
E
B±YJ27 J27
MREL
E10 B±W
II4
6
B±W(*2)
(*3)
7(*2)(*2)
BR BR
DI±62
± DIAGNOSTICSENGINE (5S±FE)
297 Author: Date:
HINT:
After confirming DTC P0125, use the OBD II scan tool or TOYOTA hand-held tester to confirm voltage output
of the heated oxygen sensor (bank 1 sensor 1) from the CURRENT DATA.
If voltage output of the heated oxygen sensor (bank 1 sensor 1) is 0 V, heated oxygen sensor (bank 1 sensor
1) circuit may be open or short.
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:

If the vehicle run out 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 warmed up or not, the air±fuel
ratio lean or rich, etc. at the time of the malfunction.

± DIAGNOSTICSENGINE (5S±FE)
DI±63
298 Author: Date:
1 Are there any other codes (besides DTC P0125) being output?
YES Go to relevant DTC chart.
NO
2 Connect OBD II scan tool or TOYOTA hand±held tester, and read value for volt-
age output of heated oxygen 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 engine to normal operating temp. (above 75°C (169°F)).
CHECK:
Read voltage output of the heated oxygen sensor (bank 1 sensor 1) when the engine is suddenly raced.
HINT:
Perform quick racing to 4,000 rpm 3 times using the accelerator pedal.
OK:
Heated oxygen sensor (bank 1 sensor 1) output a RICH signal (0.45 V or more) at least once.
OK Go to step 10.
NG
3 Check for open and short in harness and connector between ECM and heated
oxygen sensor (bank 1 sensor 1) (See page IN±31).
NG Repair or replace harness or connector.
OK