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5B.37
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
“35 Pin” (MA 1.7) Metal-Cased ECU:
a. Pin circuits 3 and/or 21 wiring or connectors.
b. Shielding for pin circuits 3 and/or 21 damaged
or not properly grounded.
c. Poor or improper grounds in system (battery,
ECU, oxygen sensor, shielding, fuel pump,
ignition output).
d. Pin circuits 3 and/or 21 routed near noisy
electrical signals (coils, spark plug lead, plug
connector).
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
“35 Pin” (MA 1.7) Metal-Cased ECU:
a. Pin circuits 12, 25 and/or 27 damaged (wiring
or connectors).
b. Pin circuits 12, 25 and/or 27 routed near noisy
electrical signal (coils, alternator).
c. Intermittent 5 volt source from ECU (pin circuit
25).
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).