Code 12, 4X Crank Signal: Notes

Fuel control 4X signal is used by PCM to determine engine speed and crankshaft position. If Codes 35 and 41 are not set, PCM detects CAM pulses and no fuel control reference pulses are monitored by PCM, Code 12 will set. Vehicle will start and run after an extended crank because when Code 12 sets, the PCM will use the spark reference 24X pulses to control fuel delivery.

1. Check to see if Code 35 is set because a REF LO problem can cause other ignition problems.
2. If Code 12 is current, condition still exists and can be diagnosed directly. If Code 12 is history, look at snapshot data to determine conditions under which code was set.
3. Check for proper output of the electronic ignition system. If voltmeter reads 4.1 volts or greater, the ignition module is able to produce 4X reference pulses.
4. Checks to see if code was set while vehicle was running or not. If MAP value is 80 kPa or less, vehicle was running as code set. Stray CAM pulses with ignition on and engine not running can cause a false Code 12.
5. Checks for 4X reference pulses on circuit No. 430 from ignition module to PCM. If PCM terminal E2 has 30-100 hertz, PCM is receiving 4X reference pulses.
6. Checks if a faulty PCM is pulling the 4X signal low.
7. Checks for short to voltage on circuit No. 430.
8. Checks if IC module is providing proper reference signal to PCM.