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DTC codes / P03xx · Ignition system and misfire / P037F

P037FGlow Plug Sense Circuit High

P037F indicates that the engine control module (ECM) has detected an abnormally high voltage on the glow plug sense circuit, which is the feedback line used to monitor glow plug operation. The ECM expects a voltage within a specific range when the glow plug is commanded on or off, and a high reading suggests an open circuit, a faulty sense connection, or a problem within the glow plug control module.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • Illumination of the check engine light or glow plug warning lamp
  • Hard starting or rough running when the engine is cold
  • Extended cranking time before the engine fires
  • White smoke from the exhaust after a cold start
  • Often no symptoms besides the warning light, especially in warm weather

Common causes, most likely first

  1. Open or damaged glow plug sense circuit wiring (broken wire, corroded terminal, or disconnected connector)
  2. Faulty glow plug control module or glow plug relay
  3. Defective glow plug with an open internal element affecting the sense feedback
  4. Poor ground connection for the glow plug circuit or engine block
  5. Water or oil intrusion into the glow plug sense connector causing high resistance
  6. ECM internal fault on the sense input circuit (rare)

How to diagnose and fix it

  1. Inspect the glow plug sense circuit wiring and connectors for damage, corrosion, or loose pins; repair or replace as needed
  2. Check the glow plug resistance with a multimeter and compare to specifications; replace any glow plug that is out of range
  3. Test the glow plug control module or relay for proper operation and replace if faulty
  4. Verify the integrity of the ground circuit for the glow plugs and the control module; clean and tighten grounds
  5. Clear the diagnostic trouble code (DTC) and perform a road test or cold-start test to confirm the repair
  6. If the code persists, perform a voltage drop test on the sense circuit and check for shorts to voltage
  7. Consult the vehicle-specific service information for pinpoint tests of the glow plug sense circuit and ECM

Sense circuit faults often misdiagnosed

  • A high voltage on the sense circuit does not always mean the glow plug itself is bad; the sense line is a feedback signal and an open in that wire will set the code even with a good glow plug.
  • Corrosion inside the glow plug connector is a common cause that can mimic a failed glow plug, so always inspect the connector before replacing parts.
  • The glow plug control module may set this code if its internal sense resistor fails, and it can be intermittent with temperature changes.
  • On some vehicles, a weak battery or charging system issue can cause voltage spikes that trigger a high sense code, so check system voltage first.
  • After repairs, the ECM may need a relearn or adaptation reset for the glow plug system to clear the code permanently.

Can I keep driving with P037F?

You can usually drive the vehicle with this code, but cold-start performance and emissions may be affected, and prolonged driving with a faulty glow plug system can damage the glow plugs or the control module. Avoid heavy loads or long idling until the fault is repaired, and address the issue promptly to prevent further damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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