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5B.40
Section 5B
EFI Fuel System
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 beyond
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.
3. Engine Wiring Harness Related
a. Difference in voltage between sensed voltage
(pin circuit 17 for metal-cased ECU, pin
circuit 2 for plastic-cased ECU) and actual
injector voltage (circuit 45/45A).
b. Problem in wiring harness.
c. ECU-to-harness connection problem.
4. Systems Related
a. Ignition (spark plug, plug wire, ignition coil.
b. Fuel (fuel type/quality, injector, fuel pressure,
fuel pump).
c. Combustion air (air cleaner dirty/restricted,
intake leak, throttle bores).
d. Base engine problem (rings, valves).
e. Exhaust system leak (muffler, flange, oxygen
sensor mounting boss, etc.).
f. Fuel in the crankcase oil.
g. Altitude.
h. Blocked or restricted fuel return circuit to tank.
Code: 42
Source: Engine (Oil) Temperature Sensor
Explanation: Not sending proper signal to ECU.
Expected Engine
Response: Engine may 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
“35 Pin” (MA 1.7) Metal-Cased ECU:
a. Pin circuits 14 and/or 27A damaged (wires,
connectors) or routed near noisy signal (coils,
alternator, etc.).
b. ECU-to-harness connection problem.
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.