Driveablity and vehicle die at times

Tiny
TIM313
  • MEMBER
  • 1996 GMC JIMMY
  • 4.3L
  • V6
  • 2WD
  • AUTOMATIC
While driving the brake light will come on and the engine seems to start misfiring, cutting out and will die at times while driving. All of this only happens when the brake light comes on. Had codes for left front wheel speed sensor, throttle position sensor. Cam shaft position sensor. Replaced throttle and cam sensors and left front abs wheel speed sensor. Light still comes on and has the driveablity problems. Codes are gone for throttle and cam sensors. But the brake codes will not clear.
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Sunday, June 14th, 2015 AT 6:14 PM

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Tiny
CARADIODOC
  • EXPERT
My first question was going to be whether that Brake light was a red light or a yellow one, since you didn't specify that, but since you mentioned a wheel speed sensor, I know you have anti-lock brakes, and that light is most likely yellow.

All of these symptoms have a very common cause on '87 and newer GM vehicles. They redesigned their generators and went from one of the world's best designs to by far the worst. Due to their design, the generators develop huge voltage spikes that can damage the internal diodes and voltage regulator, and interfere with computer sensor signals. The Engine Computer is reacting to erroneous pulses from some of its sensor. That's where the misfires and other running problems come from.

In addition, if a diode in the generator has already failed, it will generate very high "ripple" voltage which confuses the computers. The most common one to shut down is the Anti-lock Brake Computer. When it does, it turns the yellow warning light on to tell you.

The place to start is by having the charging system professionally load-tested. With a failed diode, you'll only be able to get exactly one third of the unit's rated output current. 30 amps from the common 90 amp generator isn't enough to run the entire electrical system under all conditions. Ripple voltage will be very high too when there's a bad diode.

It is real common on GM vehicles to go through four to six replacement generators in the life of the vehicle. The secret to reducing the number of repeat failures is to replace the battery at the same time, unless it is less than about two years old. It is the key component in absorbing and damping those harmful voltage spikes, but as they age and the lead flakes off the plates, they lose their ability to do that. The old battery will work fine in an '86 or older GM model or in any other brand of car.
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Sunday, June 14th, 2015 AT 7:56 PM

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