Dashboard light guide · Glass Box Diagnostics
This lamp means continuing to drive can destroy the engine or cost you control of the car. Pull over as soon as it is safe and shut the engine off.
That lamp is wired to monitor system voltage. Red means the alternator stopped charging — you are running on the battery alone and have minutes to maybe 20 minutes of drive time before the car shuts down wherever it happens to be. Pulling over now, while it is your choice, beats pushing it later.
Battery-and-alternator shotgun: it-is-usually-the-alternator — $500 part installed, problem remains because it was terminal corrosion or a TSB'd wiring pigtail.
Typical guess-and-swap cost: $400–$700 (alternator swap) when the fault was a $20 terminal, belt, or wiring repair
Voltage at the battery at rest, at idle, and at 2,000 rpm with electrical load applied; output test at the alternator sense terminal; ripple check for failed diodes; voltage-drop test on the ground circuit. Five minutes, no parts.
Codes this light commonly sets
Symptoms that come with this light
We come to you — Canyon Lake, San Antonio & Austin. Written report with root cause — see a sample.