ABS light on gauges erratic
This Chevrolet Cavalier exhibited a speedometer needle that moved up and down, a flashing warning lamp, an ABS light on, and a trouble code for low system voltage. Any time you see erratic behavior in an electrical circuit when you turn on a high power device like a heater blower motor, you should immediately suspect a poor ground somewhere in the circuit. Corroded ground connections can function just fine when there’s very little power flowing through them. But that same corrosion can drop voltage flow by 2-3 volts when you start pump lots of electrons through the rust.
In this case, a voltage drop test conducted on the ground connection with the blower on high showed a 2.2 volt drop. That’s enough of a voltage drop to cause a “low voltage” condition to the instrument cluster and the ABS system.
If you were to rely just on the trouble code (Low system voltage ABS), you’d think you had a bum battery or alternator. After spending hundreds, you’d still have the problem. So clean all ground connections first. Then reset the trouble code and see how things work.Posted on by Rick Muscoplat