2004 Pontiac Grand Prix variable speed power steering

  • 1 POST
  • 138,000 MILES

The light for tract control comes on then abs light then brake light and variable speed power steering light comes on I can feel it in the steering and brakes what would cause them all to light up could this be caused by power steering pump or bad belt or speed sensor will this effect my tranny

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Tuesday, September 3rd, 2013 AT 4:16 PM

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  • 29,781 POSTS

GM has two really huge problems that could be causing your symptoms. The first is the front wheel bearings. They develop a little play that is perfectly normal but they have wheel speed sensors built in that develop very wimpy signals to begin with, and that play allows the signals to get even weaker until the Anti-lock Brake Computer can't see them. That can happen to new wheel bearings in as little as 15,000 miles. The dealers' scrap metal bins are full of the old bearing assemblies. The loss of a signal will also cause the traction control light to turn on because that system is an addition to the anti-lock brake system. To determine if a wheel speed sensor / wheel bearing is the cause of those two lights turning on, have your mechanic read the diagnostic fault codes. Those will indicate the circuit or system that needs further diagnosis. The wheel speed data can also be read on the scanner during a test drive and you can watch if one of them drops out intermittently.

The other big problem for GM is their generators. Due to their poor design they develop huge voltage spikes that can damage the internal diodes and voltage regulator, and they can interfere with sensor signals for the other computers. One failed diode of the six will result in a loss of exactly two thirds of the generator's output current capacity. 30 amps from the common 90 amp generator is not enough to run the car's electrical system under all conditions, and the battery will have to make up the difference until it runs down. "Ripple" voltage will also be very high. With this condition system voltage can drop low enough to confuse the many computers which are very intolerant of low voltage. They may shut down or they might do weird things. Either way they are likely to turn on warning lights. To identify this the charging system must be professionally load-tested to see if the generator can deliver its design current.

If the generator has failed, replace the battery at the same time to reduce the high number of repeat failures, unless it is less than about two years old. As the battery ages it loses its ability to dampen and absorb those voltage spikes.

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Tuesday, September 3rd, 2013 AT 8:09 PM

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