P037BGlow Plug/Heater Indicator Control Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P037B is the counterpart of P037A: the control circuit of the wait-to-start lamp is too high, i.e. the line carries voltage although the engine module's driver is off, or the driver sees a short to battery voltage. GM's 2015 diesels check in the off state and set the fault after 1 s with more than 11 V; the 2016/2018 engines evaluate a short of about 0.5 Ω to a voltage source in the driver, 10 of 20 samples at 100 ms. In both cases the check engine light comes on after two trips. The lamp then stays on permanently or cannot be switched off, so the driver no longer gets a usable preheat signal; the driver may protect itself when commanded. There is no limp mode. Ford and Saab do not use P037B; CARB requires monitoring of the lamp circuit and of output components for shorts.
- What you may notice
- Glow plug light stays on or flickers
- Check engine light on (after two trips)
- No recognisable preheat indication
- Likely causes
- LikelyLamp control wire chafed against battery or ignition positive
- PossibleFault in the instrument cluster feeding voltage back
- PossibleWater damage in a connector bridging to a neighbouring pin
- RareDriver in the engine module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.