Auto Electronics: 2001 Pontiac GP 3.8L Stall & P0101 code, crankshaft position sensor, crankshaft sensor


Question
QUESTION: My Grand Prix GT with 155K miles stalls repeatedly within 10-15 miles of each drive.  It cuts out immediately...not a sputter.  It consistently throws a P0101 MAF code and I must reset from my scanner to restart and be on my way.  I have replaced the MAF sensor and checked the connector at the sensor for a loose or intermittent connection.  I have replaced the PCM with a reman and flashed with the latest firmware.  I've had it in a garage to take advantage of their diagnostic equipment and they suggested the new PCM, but have been doing all the work myself.  At this point, I'm at a loss, but I keep reading about the crankshaft sensor being a potential for causing immediate stalls.  The P0101 code baffles me though.  Any help would be appreciated.  The car runs great otherwise.  Thank you.


ANSWER: Brett, this is not a normal MAF system problem. The fact that you need to reset the PCM system codes to be on your way, suggests a shorted input to the PCM, something that is causing the module to shut down the fuel system until reset. While I would not rule out the Crankshaft position sensor as the culprit, this doesn’t sound like a normal sensor failure, that would have to be determined with a DSO (Digital Storage Oscilloscope). Having already replaced the PCM and MAF sensor (hopefully with an OEM part) should eliminate them. Searching my databases, I have found a similar vehicle with a very similar problem and fix. This was a 2000 Pontiac Bonneville with the same 3.8 motor and same symptoms, where it would cut out at highway speeds, restarting only by resetting the codes. The fix was to replace the MAP sensor! I’m not suggesting you simply replace the MAP because I’m not a fan of throwing parts a vehicle till it’s fixed. Rather, I would like to see you attempt to find the cause by further testing. Since the problem is fairly repeatable, try looking for clues by recording different sensor inputs during a test drive with your scan tool. If that goes nowhere, try disconnecting sensors one at a time then test drive to see if the cut out condition is resolved. Lastly if you cannot resolve this yourself, have someone with a Tech2 scan tool give it a look. This factory scan tool provides detailed data not available with any other tool and is your best shot at finding this unusual problem. Keep me posted, I would like to see how this turns out. I can be reached at questions@autorepairwatchdog.com.
Good luck, Don.   


---------- FOLLOW-UP ----------

QUESTION: To followup on my P0101 MAF error...this is the result.  I ended up taking the GP to a reputable Pontiac dealer.  They determined that the MAP sensor in their opinion was the problem.  The MAP sensor failing caused the PCM to think the vehicle was in a full throttle condition and somehow the MAF sensor reading contradicted this, thus causing the PCM to shutdown the engine.  I have 120 miles on the new MAP sensor and no stall.  Unfortunately, now the vehicle keeps throwing a P1404 EGR fault code, but it does not adversely effect the performance, so I'm not all that concerned about it, other than the CEL being on.  I tried to start the vehicle with the EGR unplugged, hoping that it might initiate a re-cal of some sort, but no luck.  Gotta luv the GM diagnostic system!  Thanks for your help Don.

Answer
Hello Brett, glad to hear the stalling problem is fixed. Nothing more annoying than an unreliable car. But as your new problem suggests, its always something! Again searching my database, I see that a PCM reflash has been a good fix for the problem. There is a TSB 01-06-04-018A that describes the problem but only applies to the 3.1 and 3.4 engines. I'm a bit surprised they didn't catch it at the dealership and suggest the reflash. Good luck. Don.