2002 Chevy Suburban Battery flashed; no power

JKGOWERS

MEMBER
2002 CHEVROLET SUBURBAN
V8
4WD
AUTOMATIC
150,000 MILES

The battery light flashed today while driving 2002 suburban with a history of dead batteries and alternator problems. Light stayed on, all gauges on dash went dead--windows, too and a burning smell was apparent. Haven't called for repair yet. Any idea?

1 Reply

CARADIODOC

MECHANIC
33,752 POSTS

Hi jkgowers. Welcome to the forum. GM had the second best AC generator up until 1987 when they introduced their current design. There's no way to sugar-coat it. It's a pile. It is common to go through four to six of them in the life of the vehicle. The biggest problem is the use of a switching voltage regulator that turns on and off 400 times per second. Turning off induces voltage spikes. Those spikes are shorted out by using special zener diodes for three of the six in the output circuit, but the unit is still able to cause a bunch of other seemingly unrelated driveability problems.

That's the bad news. The good news is a lot of mechanics have been finding that the replacement generator will last longer if the battery is replaced at the same time. Your old one will work fine in older cars and trucks, but as they age, their "internal resistance" goes up which reduces their ability to dampen voltage spikes.

Before you assume the generator is defective, however, see if you can locate the source of the smell. If it's coming from the generator, that's most likely all that is wrong and the things that stopped working just did so due to low system voltage. Unlike older, more reliable cars and trucks, the systems you mentioned are now all controlled by computers which are very sensitive to system voltage.

Use a cheap digital voltmeter to measure the voltage between the two battery cables with the engine off and with it running. With the engine off, it should be around 12.6 volts for a fully charged battery. If it's less than 12.0 volts, charge the battery at a slow rate for half an hour. If the voltage is less than around 11.0 volts, there is likely a shorted cell in the battery and it should be replaced before doing more testing.

With the engine running, battery voltage must be between 13.75 and 14.75 volts. If it is higher, the voltage regulator is shorted inside the generator. Replacing it is very difficult. It is common to just replace the generator. If voltage is still around 12 volts, move one meter probe from the battery's positive cable to the large nut / wire on the back of the generator. The voltage there will tell us where to go next.

Caradiodoc