1996 TOYOTA RAV4 Engine

DI−48
− DIAGNOSTICSENGINE
1996 RAV4 (RM447U)
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 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 ration at its ideal
theoretical value. The signal from the 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 devi-
ation 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 de-
tected as a malfunction and the MIL lights up.
DTC No.DTC Detecting ConditionTrouble Area
P0171
When the air fuel ratio feedback is stable after engine warning
up, the fuel trim is considerably in error on the RICH side
(2 trip detection logic)
Fuel line pressure
Injector blockage
Oxygen sensor malfunction
Manifold absolute pressure sensor
Engine coolant temp. sensor
P0172
When the air fuel ratio feedback is stable after engine warning
up, the fuel trim is considerably in error on the LEAN side
(2 trip detection logic)
Fuel line pressure
Injector blockage, leak
Oxygen sensor malfunction
Manifold absolute pressure sensor
Engine coolant temp. sensor.
HINT:
When DTC P0171 is recorded, the actual air−fuel ratio is on the LEAN side. When DTC P0172 is re-
corded, 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 detected. The MIL then
comes on.
If the total of the short−term fuel trim value and long−term fuel trim value is within ±25 %, the system
is functioning normally.
INSPECTION PROCEDURE
1 Check air induction system (See page SF−1).
NG Repair or replace.
OK
DI3ZN−01

− DIAGNOSTICSENGINE
DI−49
1996 RAV4 (RM447U)
2 Check for oxygen sensor data.
PREPARATION:
(a) Connect the OBDII scan tool or TOYOTA hand−held tester to the DLC3.
(b) Warm up engine to normal operating temperature.
CHECK:
Read the oxygen sensor output voltage and short−term fuel trim.
RESULT:
PatternOxygen sensor output voltageShort−term fuel trim
1Lean condition (Changes at 0.55 V or less)Changes at about +20 %
2Rich condition (Changes at 0.35 V or more)Changes at about −20 %
3Except 1 and 2
3 Check for oxygen sensor
(See page DI−42).
1, 2
3 Check fuel pressure (See page SF−5).
NG Check and repair fuel pump, pressure regulator,
fuel pipe line and filter (See page SF−1).
OK
4 Check injector injection (See page SF−21).
NG Replace injector.
OK
5 Check manifold absolute pressure sensor and engine coolant temp. sensor
(See page DI−21, DI−29).
NG Repair or replace.
OK

DI−50
− DIAGNOSTICSENGINE
1996 RAV4 (RM447U)
6 Check for spark and ignition (See page IG−1).
NG Repair or replace.
OK
Check and replace ECM
(See page IN−30).

− DIAGNOSTICSENGINE
DI−51
1996 RAV4 (RM447U)
DTC P0300 Random / Multiple Cylinder Misfire
Detected
DTC P0301 Cylinder 1 Misfire Detected
DTC P0302 Cylinder 2 Misfire Detected
DTC P0303 Cylinder 3 Misfire Detected
DTC P0304 Cylinder 4 Misfire Detected
CIRCUIT DESCRIPTION
Misfire: The ECM uses the crankshaft position sensor and camshaft position sensor to monitor changes in
the crankshaft rotation for each cylinder.
The ECM counts the number of times the engine speed change rate indicates that misfire has occurred. And
when the misfire rate equals or exceeds the count indicating that the engine condition has deteriorated, the
MIL lights up.
If the misfire rate is high enough and the driving conditions will cause catalyst overheating, the MIL blinks
when misfiring occurs.
DTC No.DTC Detecting ConditionTrouble Area
P0300Misfiring of random cylinder is detected during any particular
200 or 1,000 revolutionsIgnition system
Injector
Fuel line pressure
EGR
Compression pressure
Valve clearance not to specification
Valve timing
Manifold absolute pressure sensor
Engine coolant temp. sensor
P0301
P0302
P0303
P0304
For any particular 200 revolutions of the engine, misfiring is
detected which can cause catalyst overheating
(This causes MIL to blink)
For any particular 1,000 revolutions of the engine, misfiring is
detected which causes a deterioration in emissions
(2 trip detection logic)
HINT:
When the 2 or more codes for a misfiring cylinder are recorded repeatedly but no Random Misfire code is
recorded, it indicates that the misfires were detected and recorded at different times.
DI3ZO−01

S02386
1H
1DEA1
IG1 22 IG1 IG1
E4
E4
E4
E4
E4
E4 B−R
B−Y
B−R
B−Y
BR
BRE02 E01#40 #30 #20 #10ECM
Injector 8
J/B No.1
IG Switch
8 14
7
11
7 621
202
2
2
2 B−O 31
1
1
1 No.1
No.2
No.3
No.4 B−O
B−O
B−O B−O B−O12
11
25
24
13
26
EC
BatteryFusible Link Block
MAIN
W B−R2
B
B−R
B−YB−Y
B−R
J/B No.2
AM2
FI6588
FI6538
A00064
10 V/
Division10 V/
Division(Magnification)
100 m sec./Division (idling)1 m sec./Division (Idling)
Injection durationGND GND
DI−52
− DIAGNOSTICSENGINE
1996 RAV4 (RM447U)
WIRING DIAGRAM
Reference INSPECTION USING OSCILLOSCOPE
INJECTOR SIGNAL WAVEFORM
With the engine idling, measure between terminals #10, #20, #30, #40 and E01 of ECM.
HINT:
The correct waveform is as shown.

IG0317IG0151P25066A06618
1.1 − 1.3 mm
(0.043 − 0.051 in.)
A00404
”10 (+)
#30 (+)#40 (+) ON
#20 (+)
− DIAGNOSTICSENGINE
DI−53
1996 RAV4 (RM447U)
INSPECTION PROCEDURE
1 Check spark plug and spark of misfiring cylinder.
PREPARATION:
(a) Disconnect the high−tension cord from spark plug.
(b) Remove spark plug.
CHECK:
(a) Check the carbon deposits on electrode.
(b) Check electrode gap.
OK:
(1) No large carbon deposit present.
Not wet with gasoline or oil.
(2) Electrode gap: 1.1 − 1.3 mm (0.043 − 0.051 in.)
PREPARATION:
(a) Install the spark plug to the high − tension cord.
(b) Disconnect injector connector.
(c) Ground spark plug.
CHECK:
Check if spark occurs while engine is being cranked.
NOTICE:
To prevent excess fuel being injected from the injectors
during this test, do not crank the engine for more than 5 −
10 seconds at a time.
OK:
Spark jumps across electrode gap.
NG Replace or check ignition system (See page
IG−1).
OK
2 Check voltage of ECM terminal for injector of failed cylinder.
PREPARATION:
(a) Remove side trim cover (See page SF−61).
(b) Turn ignition switch ON.
CHECK:
Measure voltage between applicable terminal of ECM connec-
tor and body ground.
OK:
Voltage: 9 − 14 V
OK Go to step 4
NG

DI−54
− DIAGNOSTICSENGINE
1996 RAV4 (RM447U)
3 Check injector resistance of misfiring cylinder (See page SF−21).
NG Replace injector.
OK
Check for open and short in harness and con-
nector between injector and ECM (See page
IN−30).
4 Check fuel pressure (See page SF−5).
NG Check and repair fuel pomp, pressure regulator,
fuel pipe line and filter (See page SF−1).
OK
5 Check injector injection (See page SF−21).
NG Replace injector.
OK
6 Check EGR system (See page SF−45).
NG Repair EGR system.
OK
7 Check manifold absolute pressure sensor and engine coolant temp. sensor (See
page DI−21, DI−29).

− DIAGNOSTICSENGINE
DI−55
1996 RAV4 (RM447U)
NG Repair or replace.
OK
Check the compression pressure (See page EM−3), valve clearance (See page EM−5) and valve
timing (See page EM−19).