Powertrain Controls - ECM/PCM

Diagnostic Chart - Part 1 of 2:

Diagnostic Chart - Part 2 of 2:

Electrical Schematic:

CIRCUIT DESCRIPTION
The PCM monitors the Camshaft Position (CMP) sensor and Crankshaft Position (CKP) sensor. The PCM receives a signal from the CMP sensor and CKP sensor in the form of an Alternating Current (AC) voltage. This voltage is produced when the engine is running, a fluctuating magnetic field is generated due to changes in the air gap between the CMP sensor and distributor shaft signal rotor (CKP sensor and interrupter ring). This voltage is toggled high and low, by doing so the PCM can determine the crank angle and camshaft position. The PCM uses this information to determine when to fire the ignition coil and the fuel injectors.

DTC 12 will set if either of the following conditions are met:
^ No crank angle input detected at the PCM for 2 seconds or more while cranking engine.
^ No camshaft position input detected at the PCM for 3 seconds or more with engine speed between 600 and 4,000 rpm.

DTC CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic charts.
(Part 1 of 2)
1. Checks the resistance of the Crankshaft Position sensor.
2. Checks the resistance of the Camshaft Position sensor.
3. Checks for an open in the BLK wire between the PCM and CKP sensor.
4. Checks for an open in the WHT wire between the PCM and CKP sensor.
5. Checks for an open in the WHT wire between the PCM and Distributor.
6. Checks for an open in the BLK wire between the PCM and Distributor.
(Part 2 of 2)
7. Checks for a short to voltage or a short to ground in the BLK wire between the PCM and CKP sensor.
8. Checks for a short to voltage or a short to ground in the BLK wire between the PCM arid Distributor.
9. Checks for a short to voltage or a short to ground in the WHT wire between the PCM and CKP sensor and between PCM and Distributor.
10. Checks signal rotor air gap and faulty PCM.

DIAGNOSTIC AIDS
Check distributor cap and rotor for cracks. Also check that signal rotor air gap is adjusted properly.

Check power supply to PCM for correct voltage.

INTERMITTENT MALFUNCTIONS
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect hamess connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.