Powertrain, generic · Ignition system or misfire

P037B Glow Plug/Heater Indicator Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Lamp control wire chafed against battery or ignition positive
Fault in the instrument cluster feeding voltage back
Water damage in a connector bridging to a neighbouring pin
Driver in the engine module faulty

Symptoms

  • Glow plug light stays on or flickers
  • Check engine light on (after two trips)
  • No recognisable preheat indication

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–400
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

glow plug indicatorindicator wiringinstrument clusterengine control module

Related codes

P037AP0381P0380P0670

References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.