Battery / charging warning light on
Red battery light on the dash with engine running, or you've found the battery flat in the morning.
M117.967 uses a Bosch 80 A alternator with internal regulator. The warning bulb is part of the excitation circuit — if the bulb burns out, the alternator may not self-excite.
What the diagnosis checks
- Voltage at the battery, engine running at 1500 RPM?
- Is voltage at battery < 13.0 V at high RPM?
Possible causes it points to
- Warning bulb / excitation circuit
- Alternator brushes / regulator
- Regulator failed open (overcharging > 15 V)
Parts for this job
Cooling system serviceLoading the step-by-step diagnosis…