C1237: OBD-II code C1237 flags high battery/system voltage at the EBCM — usually caused by an overcharging alternator or a failing voltage regulator.

Symptoms

• The ABS and traction/stability control warning lamps illuminate, and other electrical accessories may behave erratically or reset.
• Interior lights and dash bulbs may burn out prematurely, and the battery can swell, vent, or leak from overcharging.
• ABS is disabled to protect the EBCM and its solenoids from damage caused by excessive supply voltage.

Common causes

• A failed alternator voltage regulator, or an internally shorted alternator, allowing charging output to rise above 15 V.
• A poor alternator ground path making the regulator sense low voltage and overcompensate, pushing overall system voltage too high.
• On computer-controlled charging systems, a failed BCM/PCM control of the alternator field circuit — confirm with related module codes.

What to do?

With the engine running at idle and at 2,000 rpm, measure battery voltage — it should stay between 13.8 and 14.5 V. If it exceeds 15 V, replace the alternator or its voltage regulator. Verify the alternator ground strap and battery cable integrity. On computer-controlled charging systems, scan for related PCM/BCM codes and address them before condemning the alternator.