DTC 12

DTC 12 Chart:

Ignition System Circuit:

CIRCUIT DESCRIPTION
The fuel control reference (4X) signal (CKT 430) is used by the PCM to determine engine speed and crankshaft position. If the PCM detects CAM pulses and no fuel control reference pulses are being received, it will set DTC 12.

DTC 12 WILL SET WHEN
- DTC 35 or 41 are not set.
- No fuel control reference pulses are received while CAM sensor pulses are being received.
- Above conditions exist for 4 seconds or more.

ACTION TAKEN (PCM WILL DEFAULT TO)
- With a current DTC 12 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- The vehicle will start and run after an extended crank with a DTC 12 set because the PCM will use the spark reference (24X) pulses to control fuel delivery.

DTC 12 WILL CLEAR WHEN
The fault no longer exists.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Check to see if DTC 35 is set because a REF LO problem can cause other ignition problems.
2. If DTC 12 is current, the condition still exists and can be diagnosed directly. If DTC 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 the voltmeter reads 4.1 volts or greater, the ignition control module is able to produce 4X reference pulses.
4. Checking to see if the DTC 12 was set while the vehicle was running or not, if MAP value is 80 kPa or less vehicle was running at code set. Stray CAM pulses at key "ON" engine not running can cause DTC 12 to set falsely.
5. Checking for 4X reference pulses on CKT 430 from the ignition control module to the PCM. If PCM terminal "E2" has between 30 and 100 Hertz, the PCM is receiving 4X reference pulses.
6. Checking if a faulty PCM is pulling the 4X signal low.
7. Checking for short to voltage on CKT 430.
8. Checking if IC module is providing proper reference signal to PCM.

DIAGNOSTIC AIDS
Vehicle will start and run after an extended crank with DTC 12 set. This is because 24X reference pulses are being received by the PCM and the PCM can use this signal for fuel control instead.