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5B.33
Section 5B
EFI Fuel System
5B
Code: 21
Source: Engine Speed Sensor
Explanation: ECU receiving inconsistent tooth
count signals from speed sensor.
Expected Engine
Response: Possible misfire as ECU attempts
to resynchronize during which time
fuel and spark calculations are not
made.
Possible Causes:
1. Engine Speed Sensor Related
a. Sensor connector or wiring.
b. Sensor loose or incorrect air gap.
c. Flywheel key sheared.
2. Speed Sensor Ring Gear Related
a. Damaged teeth.
b. Varying gap (gear loose/out of alignment).
3. Engine Wiring Harness Related
“24 Pin” (MSE 1.0) Plastic-Cased ECU:
a. Pin circuits 9 and/or 10 wiring or connectors.
b. Shielding for pin circuits 9 and/or 10 damaged
or not properly grounded.
c. Poor or improper grounds in system (battery,
ECU oxygen sensor, shielding, fuel pump,
ignition output).
d. Pin circuits 9 and/or 10 routed near noisy
electrical signals (coils, spark plug lead, plug
connector).
3. Engine Wiring Harness Related
“32 Pin” (MSE 1.1) Plastic-Cased ECU:
a. Pin circuits 9 and/or 10 wiring or connectors.
b. Shielding for pin circuits 9 and/or 10 damaged
or not properly grounded.
c. Poor or improper grounds in system (battery,
ECU, oxygen sensor, shielding, fuel pump,
ignition output).
d. Pin circuits 9 and/or 10 routed near noisy
electrical signals (coils, spark plug lead, plug
connector).
4. ECU/Harness Related
a. ECU-to-harness connection problem.
5. Ignition System Related
a. Non-resistor spark plug(s) used.
Code: 22
Source: Throttle Position Sensor (TPS)
Explanation: Unrecognizable signal is being sent
from sensor (too high, too low,
inconsistent).
Expected Engine
Response: A “limp-home” operating mode
occurs, with an overall decrease in
operating performance and efficiency.
Fuel delivery is based upon the
oxygen sensor and five mapped
values only. Rich running (black
smoke) will occur until “closed loop”
operation is initiated. A stumble or
misfire on hard acceleration and/or
erratic operation may be exhibited.
Possible Causes:
1. TPS Sensor Related
a. Sensor connector or wiring.
b. Sensor output affected or disrupted by dirt,
grease, oil, wear, or breather tube position
(must be to side opposite the TPS).
c. Sensor loose on throttle body manifold.
2. Throttle Body Related
a. Throttle shaft or bearings worn/damaged.
3. Engine Wiring Harness Related
“24 Pin” (MSE 1.0) Plastic-Cased ECU:
a. Pin circuits 4, 8, and/or 14 damaged (wiring,
connectors).
b. Pin circuits 4, 8, and/or 14 routed near noisy
electrical signal (coils, alternator).
c. Intermittent 5 volt source from ECU (pin
circuit 14).
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.