Powertrain Controls - ECM/PCM

Code 41 Flow Chart, Type 2 Ignition System:

Ignition Circuit:

*** UPDATED BY TSB #91-T-45 DATE: 2/91

CIRCUIT DESCRIPTION:

During cranking, the ignition module monitors the dual crank sensor sync signal. The sync signal is used to determine the correct cylinder pair to spark first. After the sync signal has been processed by the ignition module it sends a fuel control reference pulse to the PCM. When the PCM receives this pulse it will command all six injectors to open for one priming shot of fuel in all cylinders. After the priming, the injectors are left off for the next six fuel control reference pulses from the ignition module (two crankshaft revolutions). This allows each cylinder a chance to use the fuel from the priming shot. During this waiting period, a cam pulse will have been received by the PCM. Now the PCM begins to operate the injectors sequentially based on true camshaft position. However, if the cam signal is not present at start-up, a code 41 will set and the PCM will start sequential fuel delivery in random pattern with a 1 in 6 chance that fuel delivery is correct.

Code 41 is set when the following conditions are met:

^ Engine is running.
^ Cam sensor signal not received by PCM for last 5.0 seconds.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. This step verifies proper operation of CKTs 633, 644, and 645.

2. Step validates the integrity of CKT 630 from C3I module to PCM.

3. If the camshaft gear magnet is interfacing with the cam sensor the voltage reading will be zero, bumping engine will cause the condition to go away.

4. If the voltage reading of "BA12" is constantly varying and connection to the PCM is good, the PCM is faulty.

DIAGNOSTIC AIDS:

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check For:

^ Poor Connection or Damaged Harness - Inspect PCM harness connectors for backed out terminal "BA12," improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

^ Intermittent Test - If connections and harness check OK, monitor a digital voltmeter connected from PCM terminal "BA12" to ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change. This may help to isolate the location of the malfunction.