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5B.40
Section 5B
EFI Fuel System
Flow Chart Diagnostic Aids
Diagnostic Aid #1 “SYSTEM POWER” (MIL does not
illuminate when key is turned “on”)
Possible causes:
1. Battery
2. Main system fuse
3. MIL light bulb burned out
4. MIL electrical circuit problem
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Pin
circuits 19 and 84.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Pin
circuits 29 and 84.
5. Ignition switch
6. Permanent ECU power circuit problem
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Pin
circuit 1.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Pin
circuit 1.
7. Switched ECU power circuit problem
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Pin
circuit 2.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Pin
circuit 2.
8 ECU grounds
9. ECU
Diagnostic Aid #2 “FAULT CODES” (Refer to
detailed fault code listing before flow chart and
“servicing” information for the respective
components)
1. Code 21 - Engine Speed Synchronization
2. Code 22 - Throttle Position Sensor (TPS)
3. Code 23 - Engine Control Unit (ECU)
4. Code 31 - Oxygen Sensor
5. Code 32 - Oxygen Sensor
6. Code 33 - Fuel System (temporary adaptation
factor)
7. Code 34 - Fuel System (permanent adaptation
factor)
8. Code 42 - Engine (Oil) Temperature Sensor
9. Code 43 - TPS “Auto-Learn” Initialization
Function (Below Min. Limit), “32 Pin” (MSE 1.1)
Plastic-Cased ECU only.
10. Code 44 - TPS “Auto-Learn” Initialization
Function (Above Max. Limit), “32 Pin” (MSE 1.1)
Plastic-Cased ECU only.
11. Code 51 - Injector 1, “32 Pin” (MSE 1.1) Plastic-
Cased ECU only.
12. Code 52 - Injector 2, “32 Pin” (MSE 1.1) Plastic-
Cased ECU only.
13. Code 55 - MIL Light, “32 Pin” (MSE 1.1) Plastic-
Cased ECU only.
14. Code 56 - Pump Relay, “32 Pin” (MSE 1.1)
Plastic-Cased ECU only.
15. Code 61 - End of Fault/Blink Code Transmission
Diagnostic Aid #3 “RUN/ON” (MIL remains “on”
while engine is running)*
Possible causes:
1. Fault codes which turn on MIL when engine is
running.
a. Code 21 - Engine Speed Synchronization
b. Code 22 - Throttle Position Sensor (TPS)
c. Code 23 - Engine Control Unit (ECU)
d. Code 31 - Oxygen Sensor (shorted)
e. Code 34 - Fuel System (permanent adaptation
at limit)
f. Code 42 - Engine (Oil) Temperature Sensor
g. Code 43 - TPS “Auto-Learn” Initialization
Function (Below Min. Limit), “32 Pin”
(MSE 1.1) Plastic-Cased ECU only.
h. Code 44 - TPS “Auto-Learn” Initialization
Function (Above Max. Limit) “32 Pin”
(MSE 1.1) Plastic-Cased ECU only.
i. Code 51 - Injector 1, “32 Pin” (MSE 1.1)
Plastic-Cased ECU only.
j. Code 52 - Injector 2, “32 Pin” (MSE 1.1)
Plastic-Cased ECU only.
k. Code 55 - MIL Light, “32 Pin” (MSE 1.1)
Plastic-Cased ECU only.
l. Code 56 - Pump Relay, “32 Pin” (MSE 1.1)
Plastic-Cased ECU only.
2. MIL circuit grounded between light and ECU.
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Pin
circuit 19.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Pin
circuit 29.
3. ECU
*NOTE: The MIL in Plastic-Cased ECU systems must
be a 1/4 watt incandescent lamp.
Diagnostic Aid #4 “SPEED SENSOR” (MIL does not
turn off during cranking)
Possible causes:
1. Speed sensor
2. Speed sensor circuit problem
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Pin
circuits 9 and 10.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Pin
circuits 9 and 10.
3. Speed sensor/toothed wheel air gap
4. Toothed wheel
5. Flywheel key sheared
6. ECU