Piston Slap: The Body Control Module Electric?

Sajeev Mehta
by Sajeev Mehta
piston slap the body control module electric

Gary writes:

Good Afternoon,

Today when I got into my 2002 Saturn SL2, the power door locks started chattering. Each door, over the space of about 45 minutes, had the same thing happen. Sometimes it would be one at a time, other times it would be two or more. I also noticed that the inside locks – the “up/down” button, not the little lever you use to manually unlock the car – would not work, only later to work. For now I have removed the lock fuse and that stopped the problem. I wait and plug the fuse back in, and the sporadic chattering once again begins. Sometimes it is completely quiet. Any thoughts?

Thank you!

Sajeev answers:

Whenever a problem like this occurs, I blame something Body Control Module like. When guidance systems break down? When there’s a struggle to exist? To resist? That’s not a mere switch panel or short in chassis wiring. Oh no, Son, this is some heavy duty FAIL right here.

A body control module that’s scared out of its wits is the only culprit behind such berserk behavior. My apologies to the TTAC mothership (and all Torontonians) for such a shameful riding of RUSH’s coattails.

If I’m right, the video (below) is helpful. Ditto this Saturn forum link, complete with the body control module’s pinouts for your testing pleasure. A replacement is over $200 at Rockauto, rebuilders on eBay want over $150 for the privilege. So you’d be wise to test the wiring, get a factory shop manual and perhaps learn the proper BCM diagnosis method.

And don’t forget the BCM recall, too!

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.


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  • Kyree Kyree on May 27, 2015

    Oh yes, that will do it. I've seen body control modules fail on lots of General Motors vehicles, mainly Pontiac G6s for some reason. One indication from outside the car is when the brake lights stay on while driving, but turn off when the brake pedal is depressed.

  • Felix Hoenikker Felix Hoenikker on May 27, 2015

    Anybody know why are these modules keyed to the car's VIN?

    • See 1 previous
    • SCE to AUX SCE to AUX on May 27, 2015

      Some of them also control the odometer, whose reading needs to be implanted into the new BCM. As you know, the odometer reading is an Important Thing.

  • SCE to AUX Probably couldn't afford it - happens all the time.
  • MaintenanceCosts An ugly-a$s Challenger with poor equipment choices and an ugly Dealership Default color combination, not even a manual to redeem it, still no sale.
  • Cha65689852 To drive a car, you need human intelligence, not artificial intelligence.Unfortunately, these days even human brains are turning into mush thanks to addiction to smartphones and social media.
  • Mike1041 A nasty uncomfortable little car. Test drove in 2019 in a search for a single car that would appease two drivers. The compromise was not much better but at least it had decent rear vision and cargo capacity. The 2019 Honda HRV simply was too unforgiving and we ditched after 4 years. Enter the 23 HRV and we have a comfy size.
  • SCE to AUX I wonder who really cares about this. "Slave labor" is a useful term for the agendas of both right and left."UAW Wants Auto Industry to Stop Using Slave Labor"... but what will the UAW actually do if nothing changes?With unrelenting downward pressure on costs in every industry - coupled with labor shortages - expect to see more of this.Perhaps it's my fault when I choose the $259 cell phone over the $299 model, or the cheaper parts at RockAuto, or the lower-priced jacket at the store.Do I care about an ethical supply chain? Not really, I just want the product to work - and that's how most consumers are. We'd rather not know.Perhaps the 1990s notion of conflict-free, blood-free, ethically-sourced diamonds will find its way into the auto industry. That would be a good thing.
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