Powertrain Controls - ECM/PCM

Diagnostic Chart:

Electrical Schematic:

CIRCUIT DESCRIPTION
The ECM monitors the crank angle and the camshaft position. The ECM applies 0.70 volts to both the crank angle and the Camshaft Position (CMP) sensors. This voltage is toggled high and low by the rotation of the signal rotor. It is by the toggled voltage input that the ECM can determine the crank angle and camshaft positions.

DTC 12 will set if either of the following conditions are met:
^ No crank angle input detected at the ECM for 2 seconds or more while cranking engine.
^ No camshaft position input detected at the ECM 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 chart.
1. This checks the crank angle input low circuitry and ECM for faults.
2. This checks the crank angle input high circuitry and ECM for faults.
3. This checks the camshaft position input low circuitry and ECM for faults.
4. This checks the camshaft position input high circuitry and the ECM for faults and also for a misadjusted signal rotor air gap.

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

Check power supply to ECM 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 harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.