1990 Buick Riviera



June, 1, 2012 AT 8:32 PM

I'm stuck. The electronic dash goes haywire on my 1990 Buick Riviera. The temp gauge goes out, then the tachometer, then the cruise control and air conditioner, then the whole dash reads Error, the speedometer either reads 158 mph or 00, and the Service Engine and Electronic Malfunction lights come on. I took the car to several Buick dealers; all but one said they couldn't help me. One dealer gave it a try. After having the car for a week, they said the power module was shorting and messing up the BCM, and GM doesn't make those anymore. I found used replacements online, and the dealer has had my car for another week. They installed the used power module and BCM, but this time everything went off after about 2 minutes. The service manager said they had no way of programming the BCM, and it may be the ECM that's the problem, but they don't know how to find that out.

Does anyone have any experience with this computer equipment from the 1990 model year, and know what to do?

This car is in great shape. Hate to give it up for something like this.

Thank you!


4 Answers



June, 1, 2012 AT 8:56 PM

GM sure knows how to take care of their customers.

You might consider the generator. Since the '87 model year, they have an extremely high failure rate due to the huge voltage spikes they develop. Those spikes destroy the internal diodes and voltage regulator, and they interfere with computer sensor signals. While computers are very sensitive to low and fluctuating voltage, none are more intolerant than GM's digital dashes. In fact, on most of their vehicles with them, they switch from monitoring system voltage right at the generator to monitoring it right at the instrument cluster; it's that critical, at least in preventing annoying flickering display brightness.

I would start by having the generator load-tested with a professional tester, on the engine; don't take it off and haul it to an auto parts store. Professional load testers measure output capacity and "ripple". A bad diode will reduce the maximum output current to exactly one third of its designed output current, and ripple will be very high. Ripple is usually not displayed as a voltage. It is shown on a relative bar graph from low to high.

If you do find the generator is causing the problem, to prevent repeat failures, replace the perfectly good battery at the same time unless it is less than about two years old. As they age, they lose their ability to dampen and absorb those harmful voltage spikes.

Another way to identify if the generator is the cause of the problem is to start with a fully charged battery, then unplug the small connector on the rear, side of the generator, then see if the dash is working properly. If it is, suspect the generator. The dash should also work properly with the ignition switch turned on but without starting the engine.



June, 1, 2012 AT 9:12 PM

Thank you for the reply! I will get this to the service manager and see if this helps. Will let you know what happens.



June, 1, 2012 AT 9:19 PM

Forgot to mention there are places that rebuild computer modules, and if you do an internet search of places that repair digital dashes, there are lots of them that specialize in GM dashes. It's a real common problem. I recently had one I couldn't repair myself, so I sent it to Advanced Auto Electronics. Had it back in a week and cost less than the estimate. It acted up again two years later but this time was due to a loose ground wire under the dash.

The reasons the dealer can't help is it isn't profitable for GM to make repair parts available for the few older cars that might need them so when the supply of specialty parts runs out, you're out of luck. Ford is much worse in that regard. It's why I keep my '88 Grand Caravan on the road. I'll never have trouble finding replacement parts for that but I will for my newer vehicles. Also, GM wants you to give up on your car and buy a new one. Problem is with their very customer-unfriendly business practices there are too many people who are saying "never again" and they buy something else. GM shot themselves in the foot years ago and are paying the price now.

Used to be manufacturers made their profit from selling cars, and providing repair parts was just necessary to make their cars attractive to buyers. To make more profits they had to sell more cars, and they don't sell a car to someone who is able to repair their old one. Don't make parts available for older cars; sell more new cars.

Today there isn't as much profit in new car sales so they've switched to squeezing money from unsuspecting owners by being the sole provider of replacement parts that have to be bought at the dealership, and computers have to be programmed by them. Most of the time used computers from a salvage yard can't be put into a different car; you have to buy a new computer at the dealer. THAT'S how they're making their profits now, not from increased car sales. Either way, customers lose and they win. Only Volkswagen, BMW, and Audi are less customer friendly after the sale.



June, 1, 2012 AT 10:02 PM

Thank you for the complete response! Yes, the dealer's service manager apologized about not being able to do more. They got rid of even the service manuals for this model (I loaned him my Haynes guide). They don't know how to re-program the used computer that I got on an Internet search. It appears that wasn't the problem after all, because it's doing the exact same thing. Now I probably won't be able to get my money back on the used parts : -(

My wife so wants to keep this car until it reaches Antique status in 3 years and we don't have to pay for tags : -)

I hope what you've suggested will solve the problem. It's a great car except for this. Can't abide driving in Mississippi heat without air conditioning!

Thanks again for your thorough response.

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