P037B code meaning
Glow Plug/Heater Indicator Control Circuit High
Powertrain system Generic code P03xx codes Check engine light
What P037B means
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.
P037B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P037B
- Glow plug light stays on or flickers
- Check engine light on (after two trips)
- No recognisable preheat indication
Common causes of P037B
- Most 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
- Less likelyDriver in the engine module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Glow plug indicatorIndicator wiringInstrument clusterEngine control module
What each part of P037B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 3 | Area: ignition system or misfire. |
| 7B | The exact fault in that area. |
What to do next
- Note P037B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P037B
What does P037B mean?
P037B means "Glow Plug/Heater Indicator Control Circuit High". P037B is the counterpart of P037A: the control circuit of the wait-to-start lamp is too high, i.e. It is a generic code, so it means the same on every make.
Is it safe to drive with P037B?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P037B fail an emissions test?
Yes, it can. P037B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P037B to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will P037B clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.