SERVICE MANUAL UPDATE SEC.8D1 ECM TROUBLE CODE DIAGNOSIS

SUBJECT: SERVICE MANUAL UPDATE - SECTION 8Dl - REVISED ECM TROUBLE CODE E041 DIAGNOSTIC CHART AND FACING PAGE

MODELS AFFECTED: 1988-90 RIVIERA MODELS

This bulletin updates the Code E041 Diagnostic Chart and Facing Page in "ECM Trouble Code Diagnosis" Section 8Dl for 1988-1990 Rivieras.

The revised chart addresses the possibility of a faulty ignition module causing Code E041 to be set by not supplying the CAM sensor signal to the ECM.

CODE E041 CAM SENSOR CIRCUIT 3800 (VIN C) (PORT)

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 ECM. When the ECM 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 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 ECM. Now the ECM begins to operate the injectors sequentially based on true camshaft position. However, if the cam signal is not present at start-up, a Code E041 will set and the ECM will start sequential fuel delivery in random pattern with a 1 in 6 chance that fuel delivery is correct.

Code E041 is set when the following conditions are met:

o Engine is running. o Cam sensor signal not received by ECM for last 2 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 the ignition module to ECM.

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 "BC5" is constantly varying and connection to terminal "BC5" are good, the ECM 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:

o Poor Connection or Damaged Harness Inspect ECM harness connectors for backed out terminal "BC5", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

o Intermittent Test If connections and harness check OK, monitor a digital voltmeter connected from ECM terminal "BC5" 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.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.