Powertrain, generic · Ignition system or misfire

P037A Glow Plug/Heater Indicator Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Diesel engines show the driver a wait-to-start lamp while the glow plugs preheat; the engine module switches it with a high-side driver. P037A means the lamp control circuit is too low – in practice a short to ground on the line to the instrument cluster. GM's diesels detect it in the driver itself: about 0.5 Ω to ground with the lamp commanded, only with a lamp configured, ignition on, more than 11 V and not while cranking. The 2015 engines need 3 s of fault, the 2016/2018 engines 10 of 15 samples; the check engine light follows after two trips. The glow plugs keep working; only the indication is missing, so the driver may start too early. CARB requires monitoring of the wait-to-start lamp circuit. Ford reports lamp faults under P0381 and does not use P037A.

Likely causes

Lamp control wire chafed through to ground between engine module and cluster
Lamp or LED driver in the instrument cluster shorted internally
Moisture or corrosion in the module or cluster connector
Driver in the engine module faulty

Symptoms

  • Glow plug light does not come on or stays dim
  • Check engine light on (GM after two trips)
  • Driver starts too early, possibly poor cold start

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

P037BP0381P0380P0670P0683

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