90 Riviera Electronic Dash issues

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.

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.