426 Section 4 Computer Control Technology
Computer System Sensor and Actuator Diagnosis
Condition Possible Causes Correction
Poor performance and gas
mileage.
1. Faulty coolant temperature sensor.
2. Faulty air temperature sensor.
3. Maladjusted or defective throttle position sensor.
4. Faulty EGR position sensor.
5. Defective or contaminated oxygen sensor.
6. Maladjusted or faulty crankshaft position sensor.
7. Faulty manifold absolute pressure sensor.
8. Bad mass airfl ow sensor.
9. Bad fuel injectors.
Test components and related
circuitry. Service or replace as
necessary.
Erratic acceleration. 1. Faulty EGR position sensor. Test sensor and related circuitry.
Service as necessary.
Pinging. 1. Bad coolant temperature sensor.
2. Maladjusted or defective throttle position sensor.
3. Defective EGR position sensor.
4. Faulty manifold absolute pressure sensor.
5. Bad mass airfl ow sensor.
6. Faulty knock sensor.
Test sensors and related
circuitry. Service or replace as
necessary.
Surging at highway speeds. 1. Bad coolant temperature sensor.
2. Maladjusted or defective throttle position sensor.
3. Defective EGR position sensor.
4. Faulty manifold absolute pressure sensor.
5. Bad mass airfl ow sensor.
Test sensors and related
circuitry. Service or replace as
necessary.
Backfi ring. 1. Maladjusted or defective throttle position sensor.
2. Faulty manifold absolute pressure sensor.
3. Bad mass airfl ow sensor.
Test sensors and related
circuitry. Service or replace as
necessary.
Black exhaust smoke. 1. Bad coolant temperature sensor.
2. Faulty intake air temperature sensor.
3. Faulty oxygen sensor.
4. Faulty manifold absolute pressure sensor.
5. Bad mass airfl ow sensor.
6. Bad fuel injectors.
Test components and related
circuitry. Service or replace as
necessary.
No torque converter lockup. 1. Maladjusted or defective throttle position sensor.
2. Faulty EGR position sensor.
3. Faulty manifold absolute pressure sensor.
4. Bad mass airfl ow sensor.
5. Faulty torque converter lockup solenoid.
6. Faulty or maladjusted brake light switch.
Test components and related
circuitry. Service or replace as
necessary.
Run on. 1. Defective idle speed motor. Test motor and related circuitry.
Service or replace as necessary.