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5B.36
Section 5B
EFI Fuel System
Code: 42
Source: Engine (Oil) Temperature Sensor
Explanation: Not sending proper signal to ECU.
Expected Engine
Response: Engine will be hard to start because
ECU can’t determine correct fuel
mixture.
Possible Causes:
1. Temperature Sensor Related
a. Sensor wiring or connection.
2. Engine Wiring Harness Related
"24 Pin" (MSE 1.0) Plastic-Cased ECU:
a. Pin circuits 4, 6 and/or 4A damaged (wires,
connectors) or routed near noisy signal (coils,
alternator, etc.).
b. ECU-to-harness connection problem.
2. Engine Wiring Harness Related
"32 Pin" (MSE 1.1) Plastic-Cased ECU:
a. Pin circuits 4, 6 and/or 4A damaged (wires,
connectors) or routed near noisy signal (coils,
alternator, etc.).
b. ECU-to-harness connection problem.
3. System Related
a. Engine is operating above the 176°C (350°F)
temperature sensor limit.
Code: 43 and 44 “32 Pin” (MSE 1.1)
Plastic-Cased ECU only.
Source: TPS “Auto-Learn” initialization
function failed, throttle angle out of
learning range.
Explanation: While performing the TPS “Auto-
Learn” function, the measured
throttle angle was not within
acceptable limits.
Expected Engine
Response: MIL illuminated. Engine will continue
to run but not properly. Upon restart
TPS Auto-Learn function will run
again unless voltage to ECU
disconnected to clear memory.
Possible Causes:
1. TPS Related
a. TPS rotated on throttle shaft assembly out of
allowable range.
b. TPS bad.
2. Engine Wiring Harness Related
a. Broken or shorted wire in harness.
ECU pin 18 to TPS pin 1.
ECU pin 4 to TPS pin 2.
ECU pin 8 to TPS pin 3.
3. Throttle Body Related
a. Throttle shaft inside TPS worn, broken, or
damaged.
b. Throttle plate loose or misaligned.
c. Throttle plate bent or damaged allowing extra
airflow past, or restricting movement.
4. ECU Related
a. Circuit providing voltage or ground to TPS
damaged.
b. TPS signal input circuit damaged.
5. Oxygen Sensor/Harness Related.
a. Oxygen sensor bad.
b. Wiring problem to oxygen sensor.
c. Muffler leak (causing O
2
sensor to falsely
indicate a lean condition).
d. Bad ground between ECU and engine.
Code: 51 “32 Pin” (MSE 1.1) Plastic-
Cased ECU only.
Source: Injector #1 circuit open, shorted to
ground, or shorted to battery.
Explanation: Injector #1 is not functioning because
the circuit is open, shorted to ground,
or shorted to battery.
Expected Engine
Response: Engine will run very poorly with only
one cylinder functioning.
Possible Causes:
1. Injector Related
a. Injector coil shorted or opened.
2. Engine Wiring Harness Related
a. Broken or shorted wire in harness.
ECU pin 14 to injector pin 2. ECU pin 28 to
fuel pump relay pin 86. Note: after key-off
then key-on, code 56 would be set also. Fuel
pump relay pin 87 to injector pin 1.
b. Open main fuse F1.