Questions and Answers

Pontiac Bonneville DTC P0321 Q. I have a 1994 Pontiac Bonneville SSE (non-supercharged) 3.8 liter V-6 with an automatic transmission, 167,800 miles, fuel injection, ABS, P/S, A/C, cruise control, traction control, auto-level control on rear shocks and rack and pinion steering. My question has to do with my engine stalling after running just under 15 minutes.

I had a shop read the stored trouble codes. The only code provided was DTC P0321. I followed the ALLDATA flow chart for determining the cause with no change to the original problem: stalling.

I have connected an analog voltmeter between the spark reference circuit (number 647) and reference ground such that I can monitor the voltage while driving. The voltage is 5 VDC before the engine starts and drops to 2.5 VDC when running. The voltage remains at 2.5 VDC for about 10-15 minutes and then goes back up to about 5 VDC.

Shortly after this increase in voltage the engine will stall. It does not matter whether the engine speed is above 1200 RPM or not. It will still stall. The engine will re-start and run for about 1 minute and then stall again.

Upon re-starting again the Traction Control is disabled. I presume that this is done by the PCM because it cannot be turned back on until the engine is turned off again. However, upon this second re-start (Traction Control disabled) the voltage on the spark reference circuit is now once again at 2.5 VDC and the engine will continue running but with less power.

My question is whether or not the stalling can be related to the Traction Control system or is it likely still to be in the ignition circuit? One more bit of information, about two weeks before this started occurring I replaced both front wheel bearing assemblies which have speed sensors integral to the bearing assembly.

My thought was that these speed sensors may not be working correctly, thereby causing a Traction Control problem that affects the engine.

I have already replaced the wire from the Ignition Control Module to the 8 way harness connector, the Ignition Control Module, spark plugs and wire set to eliminate these components as contributors to the situation.

Any information of suggestions on what to check for will be greatly appreciated.

Thanks,
Len

A. P0321 Spark Reference Circuit. The spark reference signal is used by the PCM to improve ignition timing accuracy during crank and at engine speeds of up to 1,200 RPM. The spark reference circuit allows the use of ignition control mode below 400 RPM, eliminating the need to utilize module mode during start-up, and also allows the PCM to calculate true crankshaft position in 1/6 the time that use of the fuel control reference signal would permit.

During normal operation, the PCM uses the spark reference signal to control ignition timing until the engine speed exceeds 1200 RPM, at which time the fuel control reference signal is used. There is no connection to the TCS.

If you are using Alldata then it's pretty much spelled out there. If everything else checks out, then you're probably looking at a bad PCM.

Added 7/17/03:

I thought you might be interested in feed-back regarding the cause of my car’s problem with code DTC P0321.

Before replacing the PCM I decided to check the second output from the Crankshaft Position Sensor, circuit 646, input to the Ignition Control Module. I hadn’t checked it before since it was not on ALLDATA’s flow chart. I put a volt meter on circuit 647 as before, and a volt meter on circuit 646.

The voltage on circuit 646 was stable until 14 minutes of running time elapsed. The voltage then changed +1/2 volts to 5.5 VDC. A few seconds later circuit 647 jumped from 2.5 to 5 VDC and the engine stalled.

I replaced the Crankshaft Position Sensor which eliminated the stalling problem. Thanks for giving consideration to my problem and keep up the helpful assistance for those of us who still fix our own autos.

Len