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5B.34
Section 5B
EFI Fuel System
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
the 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) 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 richif 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
mixtureis 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 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.
Code: 32
Source: Oxygen Sensor
Explanation: No change in the sensor output
signal.
Expected Engine
Response: “Open loop” operation only, may
cause a drop in system performance
and fuel efficiency.
Possible Causes:
1. Engine Wiring Harness Related
a. Pin circuit 11 wiring or connectors.
Pin 11 for “24 Pin” (MSE 1.0) Plastic-Cased
ECU.
Pin 20 for “32 Pin” (MSE 1.1) Plastic-Cased
ECU.
2. Oxygen Sensor Related
a. Sensor connector or wiring problem.
b. Sensor contaminated or damaged.
c. Sensor below the minimum operating
temperature (375°C, 709°F).
d. Poor ground path from sensor to engine
(sensor grounds through shell, see Oxygen
Sensor section).