1999 TOYOTA CAMRY Service Repair Manual

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Page 1289 of 4592

TOYOTA CAMRY 1999 Service Repair Manual ± DIAGNOSTICSENGINE (5S±FE)
DI±77
312 Author: Date:
DTC P0136 Heated Oxygen Sensor Circuit Malfunction
(Bank 1 Sensor 2)
CIRCUIT DESCRIPTION
Refer to DTC P0125 (Insufficient Coolant Temp. for Clo

Page 1290 of 4592

TOYOTA CAMRY 1999 Service Repair Manual DI±78
± DIAGNOSTICSENGINE (5S±FE)
313 Author: Date:
2 Check for open and short in harness and connector between ECM and heated
oxygen sensor (See page IN±31).
NG Repair or replace harness or co

Page 1291 of 4592

TOYOTA CAMRY 1999 Service Repair Manual ± DIAGNOSTICSENGINE (5S±FE)
DI±79
314 Author: Date:
DTC P0171 System too Lean (Fuel Trim)
(Only for California Spec.)
DTC P0172 System too Rich (Fuel Trim)
(Only for California Spec.)
CIRCUIT DES

± DIAGNOSTICSENGINE (5S±FE)
DI±79
314 Author: Date:
DTC P0171 System too Lean (Fuel Trim)
(Only for California Spec.)
DTC P0172 System too Rich (Fuel Trim)
(Only for California Spec.)
CIRCUIT DESCRIPTION
Fuel trim refers to the feedback compensation value compared against 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
When air±fuel ratio feedback is stable after engine warming up,
fuel trim is considerably in error on rich side
(2 trip detection logic)
Gas leakage on exhaust system
Air intake (loose hoses)
Fuel line pressure
Injector blockage
Manifold absolute pressure sensor
Engine coolant temp. sensor
A/F sensor
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)
Gas leakage on exhaust system
Fuel line pressure
Injector leak, blockage
Manifold absolute pressure sensor
Engine coolant temp. sensor
A/F sensor
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.
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.
DI1JW±03

Page 1292 of 4592

TOYOTA CAMRY 1999 Service Repair Manual DI±80
± DIAGNOSTICSENGINE (5S±FE)
315 Author: Date:
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 TOYOT

Page 1293 of 4592

TOYOTA CAMRY 1999 Service Repair Manual ± DIAGNOSTICSENGINE (5S±FE)
DI±81
316 Author: Date:
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

Page 1294 of 4592

TOYOTA CAMRY 1999 Service Repair Manual DI±82
± DIAGNOSTICSENGINE (5S±FE)
317 Author: Date:
7 Check output voltage 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

Page 1295 of 4592

TOYOTA CAMRY 1999 Service Repair Manual ± DIAGNOSTICSENGINE (5S±FE)
DI±83
318 Author: Date:
8 Check for open and short in harness and connector between ECM and oxygen
sensor (See page IN±31).
NG Repair or replace harness or connector.

Page 1296 of 4592

TOYOTA CAMRY 1999 Service Repair Manual DI±84
± DIAGNOSTICSENGINE (5S±FE)
319 Author: Date:
DTC P0171 System too Lean (Fuel Trim)
(Except California Spec.)
DTC P0172 System too Rich (Fuel Trim)
(Except California Spec.)
CIRCUIT DESCRIP

DI±84
± DIAGNOSTICSENGINE (5S±FE)
319 Author: Date:
DTC P0171 System too Lean (Fuel Trim)
(Except California Spec.)
DTC P0172 System too Rich (Fuel Trim)
(Except California Spec.)
CIRCUIT DESCRIPTION
Fuel trim refers to the feedback compensation value compared against 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 heated oxygen sensor indicates whether the air±fuel ratio is RICH or
LEAN compared to the ideal theoretical value, triggering a reduction in fuel volume if the air±fuel 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 due to individual engine differences, wear over time and
changes in the usage environment.
If both the short±term fuel trim and long±term fuel trim are LEAN or RICH beyond 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)
Gas leakage on exhaust system
Air intake (hose loose)
Fuel line pressure
Injector blockage
Heated oxygen sensor (bank 1 sensor 1)
Manifold absolute pressure sensor
Engine coolant temp. sensor
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)
Gas leakage on exhaust system
Fuel line pressure
Injector leak, blockage
Heated oxygen sensor (bank 1 sensor 1)
Manifold absolute pressure sensor
Engine coolant temp. sensor
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 heated oxygen sensor (bank 1 sensor 1) output voltage and the short±term fuel trim value can
be read using the OBD II scan tool or TOYOTA hand±held tester.
DI4NG±01

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