1999 TOYOTA CAMRY light

± 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

P25430
ECM
Throttle Body
EGR
Vacuum
Modulator EGR Valve
VSV
Exhaust Gas Throttle
Valve
u
± DIAGNOSTICSENGINE
DI±63
DTC P0400 Exhaust Gas Recirculation Flow Malfunction
CIRCUIT DESCRIPTION
The EGR system recirculates exhaust gas, which is controlled to the proper quantity to suit the driving condi-
tions, into the intake air mixture to slow down combustion, reduce the combustion temperature and reduce
NOx emissions. The amount of EGR is regulated by the EGR vacuum modulator according to the engine
load.
If even one of the following conditions is fulfilled, the VSV is
turned ON by a signal from the ECM.
This results in atmospheric air acting on the EGR valve, closing
the EGR valve and shutting off the exhaust gas (EGR cut±off).
Under the following conditions, EGR is cut to maintain driveabil-
ity.

Before engine is warmed up.

During deceleration (throttle valve closed).

Light engine load (amount of intake air very small).

Engine idling.

Engine speed over 4,400 rpm.

High engine load (amount of intake air very large).
DTC No.DTC Detecting ConditionTrouble Area
P0400
After engine is warmed up, intake manifold absolute pressure
is larger than value calculated by ECM while EGR system is
ON (2 trip detection logic)

Vacuum or EGR hose is connected to wrong post

Open or short in VSV circuit for EGR

VSV for EGR

EGR system

EGR vacuum modulator

EGR valve

Manifold absolute pressure sensor

ECM
DI64W±01

A09397
ECM
J18
J/C
7 From
Battery
B
213
EFI Relay VSV
for EGR
21P-B23
E6EGR
E01
2K2
2J EFI
Engine Room J/B No.2 1B 9
B-Y
B
2AB-Y
IG3
EB
W-B
2F4B-Y
5
B-YFrom
Ignition SW
P20769
Vehicle Speed
60 ± 80 km/h
(38 ± 50 mph)
Idling
IG SW OFF
(1)(2)
Warm up
3 ± 5 min.2 min.
3 ± 5 min.Time (3)
(4)
(5)(6)
(7)
2 min. DI±64
± DIAGNOSTICSENGINE
WIRING DIAGRAM
SYSTEM CHECK DRIVING PATTERN
(1) Connect the OBD II scan tool or TOYOTA hand±held tester to the DLC3.
(2) Start and warm up the engine with all the accessories switched OFF.
(3) Run the vehicle at 60 ± 80 km/h (38 ± 50 mph) for 3 min. or more.
(4) Idle the engine for about 2 min.
(5) Do steps (3) and (4) again.
(6) Stop at safe place and turn the ignition switch OFF.
(7) Do steps (2) to (5) again.
(8) Check the READINESS TESTS mode on the OBD II scan tool or TOYOTA hand±held tester.
If COMPL is displayed and the MIL does not light up, the system is normal.
If INCMPL is displayed and the MIL does not light up, run the vehicle again and check it.
HINT:
INCMPL is displayed when either condition (a) or (b) exists.
(a) The system check is incomplete.

A00407
Air
Air FilterAir
E
System: OFFSystem: ON GG E
± DIAGNOSTICSENGINE
DI±65
(b) There is a malfunction in the system.
If there is a malfunction in the system, the MIL will light up after steps (2) to (5) above are done. (2 trip
detection logic)
INSPECTION PROCEDURE
HINT:

If DTCs P0105, P0106 and P0400 are output simultaneously, perform troubleshooting of DTC P0105
first.

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.
TOYOTA hand±held tester:
1 Check connection of vacuum hose and EGR hose (See Pub. No. RM654U, page
EC±12).
NG Repair or replace.
OK
2 Check VSV for EGR.
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.
(c) Select the ACTIVE TEST mode on the TOYOTA hand±
held tester.
CHECK:
Check the operation of the VSV when it is operated by the TOY-
OTA hand±held tester.
OK:
EGR system is OFF:
Air from port E is flowing out through the air filter.
EGR system is ON:
Air from port E is flowing out port G.
OK Go to step 4.
NG
3 Check operation of VSV for EGR (See Pub. No. RM654U, page SF±43).

DI±80
± DIAGNOSTICSENGINE
(1) Connect the TOYOTA hand±held tester to the DLC3.
(2) Switch the TOYOTA hand±held tester from the normal mode to the check mode (See page
DI±3).
(3) Start the engine and warm it up with all accessory switches OFF.
(4) Drive the vehicle at 60 ± 120 km/h (38 ± 75 mph) and engine speed at 1,600 ± 3,200 rpm for 3
- 5 min.
HINT:
If a malfunction exists, the MIL will light up during step (4).
NOTICE:
If the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
If you do not have a TOYOTA hand±held tester, turn the ignition switch OFF after performing steps
(3) and (4), then perform steps (3) and (4) again.
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 P1130) 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 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 AF± 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)

A09400
ECM
STP 4
E4
G±W G±WJ23 J24 1R 1R
1SJ27 J/C
AC Instrument Panel J/B
5
2 4
7
12
G±WLight
Failure
Sensor
Stop
Light
(LH) Stop
Light
(RH) G±R
2
52
5
W±B
W±B
BM High
Mount
Stop
Light
2
1R
A
A
J34
J/C
BL
1
W±B
Stop Light
Switch
2
BatteryW±B W
1C 7
STOP
41BInstrument
Panel J/B
B±R
B±R
F14
2 F14
1
ALT
F9MAIN
FL
FL Block
G±W
1
B±G
DI±108
± DIAGNOSTICSENGINE
DTC P1520 Stop Light Switch Signal Malfunction
CIRCUIT DESCRIPTION
This signal is used to detect when the brakes have been applied. The STP signal voltage is the same as
the voltage supplied to the stop lights. The STP signal is used mainly to control the fuel cut±off engine speed.
(The fuel cut±off engine speed is reduced slightly when the vehicle is braking.)
DTC No.DTC Detecting ConditionTrouble Area
P1520Stop light switch does not turn off even once vehicle is driven
(2 trip detection logic)
Short in stop light switch signal circuit

Stop light switch

ECM
WIRING DIAGRAM
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 operation of stop light.
PREPARATION:
Check if the stop lights go on and off normally when the brake pedal is operated and released.
NG Check and repair stop light circuit
(See Pub. No. RM654U, page BE±37).
DI01H±09

A09282
BE6653Q06993A09270
Brake Pedal
Depressed ON
Brake Pedal
Released
STP
(±) (+)
± DIAGNOSTICSENGINE
DI±109
OK
2 Check STP signal.
When using TOYOTA hand±held tester:
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 STP signal on the TOYOTA hand±held tester.
OK:
Brake PedalSTP Signal
DepressedON
ReleasedOFF
When not using TOYOTA hand±held tester:
PREPARATION:
Turn the ignition switch ON.
CHECK:
Check the voltage between terminal STP of the ECM connector
and body ground.
OK:
Brake PedalVoltage
Depressed7.5 ± 14 V
ReleasedBelow 1.5 V
OK Check for intermittent problems
(See page DI±3).
NG
3 Check harness and connector between ECM and stop light switch
(See page IN±29).
NG Repair or replace harness or connector.
OK
Check and replace ECM (See page IN±29).

DI02U±04
Vehicle Brought to Workshop
Customer Problem Analysis
Check DTC and Freeze Frame Data (Precheck)
Record or Print DTC and Freeze Frame Data P.
DI±133
Clear DTC and Freeze Frame Data P. DI±133
Visual Inspection
Setting the Check Mode Diagnosis P.
DI±133
1
Items insideare titles of pages in this manual, with the
page number indicated in the bottom portion. See the indicated
pages for detailed explanations.
P.
DI±132
Connect an OBD II scan tool or TOYOTA hand±held tester to DLC3.
If the display shows ºUNABLE TO CONNECT TO VEHICLEº when you have connected the
scan tool / TOYOTA hand±held tester, inspect DLC3 P.
DI±133
2
3
4
5
6
Symptom does not occur
Problem Symptom Confirmation8
7Symptom Simulation
P.
IN±19Symptom occurs
DTC CheckP. DI±133OK Code11Preliminary Check
P.
DI±133
DTC Chart
P. DI±145Mechanical System Test
P.
DI±133
Manual Shifting Test
P.
DI±133 OK
OK
Chapter 1
(Electronic)Chapter 2
(On±Vehicle)
P.
DI±148 OK
Chapter 3
(Off±Vehicle)OK Problem Symptoms Table± P. DI±148
Circuit
Inspection
O/D Cancel Signal Check

O/D Main Switch & O/D OFF Indica-
tor Light Circuit Check
NG
Parts Inspection
NG
NGNG
Identification of ProblemRepairConfirmation TestEnd
NG
NG
12
13
14
15
16 17 9
10
P. DI±148P. DI±148
P. DI±151 to DI±171
OK
± DIAGNOSTICSAUTOMATIC TRANSAXLE
DI±131
201 Author: Date:
AUTOMATIC TRANSAXLE
HOW TO PROCEED WITH TROUBLESHOOTING