Powertrain Controls - ECM/PCM

DTC 12 - No RPM Signal:

RPM Signal Circuit:

Circuit Description:
The powertrain control module (PCM) monitors the crank angle and the camshaft position. The PCM applies 0.70 volts to 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 PCM can determine the crank angle and camshaft positions.

DTC 12 will set if either of the following conditions are met:

(1) No crank angle input detected at the PCM for 2 seconds or more while cranking engine.

(2) No camshaft position input detected at the PCM for 3 seconds or more with engine speed between 600 and 4,000 rpm.

Test Description:
Numbers below refer to circled numbers on the diagnostic chart.

1. This checks the crank angle input low circuitry and PCM for faults.

2. This checks the crank angle input high circuitry and PCM for faults.

3. This checks the camshaft position input low circuitry and PCM for faults.

4. This checks the camshaft position input high circuitry and the PCM 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.

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.