P037F: Glow Plug Sense Circuit High

P037F means the voltage read back from the glow plug supply is too high. GM's 2016/2018 diesels set it when the feedback lies above a threshold derived from the run/crank relay voltage, with a feedback above 5.0 V – for example voltage is reported although the plugs are not energised, or the sense line is shorted to positive. The code needs 40 of 80 samples at 50 ms, about 2 of 4 s, only with the engine running, and turns on the check engine light after two trips; GM classes the cause as internal to the module. If there is a real short to positive or a stuck relay or output stage, the plugs can stay energised permanently, overheating them and draining the battery – then also check the single plug codes P0671 ff and P066x. CARB requires glow plug circuits to be monitored for correct current and voltage drop.

Symptoms

• Check engine light on
• Glow plugs possibly energised permanently (flat battery, plug damage)
• Glow plug light implausible

Most likely causes

• Sense wire chafed against positive or bridged in the connector
• Glow relay sticking or output stage shorted (supply stays on)
• Measuring circuit in the engine module

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the fuse and connector
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Measure the resistance of each glow plug with the engine cold
4. Check the power supply during the preheat cycle
5. Test the module or relay if the glow plugs are good

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P037F means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 3: Ignition and misfires
• 7F: Specific fault in that system

Frequently asked questions

Can I keep driving with code P037F?

You can keep driving, although cold starts will be harder. Avoid cranking the starter repeatedly on cold days.

What causes code P037F?

The most common causes are: sense wire chafed against positive or bridged in the connector; glow relay sticking or output stage shorted (supply stays on); measuring circuit in the engine module.

Related codes

• P037DGlow Plug Sense Circuit
• P037EGlow Plug Sense Circuit Low
• P066BCylinder 1 Glow Plug Control Circuit High
• P0671Cylinder 1 Glow Plug Circuit/Open
• P0670Glow Plug Control Module 1 Control Circuit/Open

Sources

• gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 16OBDG04 Engine Diagnostics
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.