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5B.38
Section 5B
EFI Fuel System
3. Engine Wiring Harness Related
“32 Pin” (MSE 1.1) Plastic-Cased ECU:
a. Pin circuits 4, 8, and/or 18 damaged (wiring,
connectors).
b. Pin circuits 4, 8, and/or 18 routed near noisy
electrical signal (coils, alternator).
c. Intermittent 5 volt source from ECU (pin circuit
18).
4. ECU/Harness Related
a. ECU-to-harness connection problem.
Code: 23
Source: ECU
Explanation: ECU is unable to recognize or process
signals from its memory.
Expected Engine
Response: Engine will not run.
Possible Causes:
1. ECU (internal memory problem).
a. Diagnosable only through the elimination of all
other system/component faults.
Code: 24 (Will not blink out)
Source: Engine Speed Sensor
Explanation: No tooth signal from speed sensor.
MIL light will not go out when
cranking.
Expected Engine
Response: None-engine will not start or run as
ECU is unable to estimate speed.
Possible Causes:
1. Engine Speed Sensor Related
a. Sensor connector or wiring.
b. Sensor loose or air gap incorrect.
2. Speed Sensor Wheel Related
a. Damaged teeth.
b. Gap section not registering.
3. Engine Wiring Harness Related
a. Pin circuit wiring or connectors.
Pin(s) 3 and/or 21 for “35 Pin” (MA 1.7)
Metal-Cased ECU.
Pin(s) 9 and/or 10 for “24 Pin” (MSE 1.0)
Plastic-Cased ECU.
Pin(s) 9 and/or 10 for “32 Pin” (MSE 1.1)
Plastic-Cased ECU.
4. ECU/Harness Related
a. ECU-to-harness connection problem.
Code: 31
Source: Fuel Mixture or Oxygen Sensor
Explanation: “System too lean.” Oxygen sensor not
sending expected voltage to ECU.
Expected Engine
Response: System operates under “open loop”
control only. Until fault is detected and
registered by ECU, engine will run rich
if oxygen sensor is shorted to ground
or lean if it is shorted to battery
voltage. After fault is detected,
performance can vary, depending on
cause. If performance is pretty good,
the problem is probably with the
oxygen sensor, wiring, or connectors.
If the engine is still running rich
(laboring, short on power) or lean
(popping or misfiring), the fuel mixture
is suspect, probably incorrect TPS
initialization or low fuel pressure.
Possible Causes:
1. TPS Initialization Incorrect
a. Lean condition (check oxygen sensor signal
with VOA and see Oxygen Sensor section).
2. Engine Wiring Harness Related
a. Pin circuit wiring or connectors.
Pin 10 for “35 Pin” (MA 1.7) Metal-Cased
ECU.
Pin 11 for “24 Pin” (MSE 1.0) Plastic-Cased
ECU.
Pin 20 for “32 Pin” (MSE 1.1) Plastic-Cased
ECU.
3. Low Fuel Pressure
4. Oxygen Sensor Related
a. Sensor connector or wiring problem.
b. Exhaust leak.
c. Poor ground path to engine (sensor is case
grounded).
5. Poor system ground from ECU to engine, causing
rich running while indicating lean.