P037D
Glow Plug Sense Circuit.
- Generic
- Powertrain
- Generic code
- Low severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 3
- AreaIgnition system or misfire
- 7D
- FaultThe specific fault in that area
What it means
P037D means the control unit has detected a fault in the glow plug sense circuit, the signal used to monitor glow plug voltage, current or status. It is set when the sensed value is outside the expected range, missing or implausible compared with what was commanded. Whether the monitoring is in the engine control unit or a separate glow plug module, and how many circuits it covers, depends on the vehicle and engine.
Symptoms
- Engine management warning light on, and possibly a glow plug warning light
- Hard starting or extended cranking on cold mornings
- White smoke and rough running just after a cold start
- Misfire or uneven idle until the engine warms up
- Higher emissions or poorer cold-start economy
- No noticeable symptoms when the engine is warm
Possible causes
- Faulty or failing glow plug (open circuit, high resistance or short)likely
- Damaged, corroded or loose wiring and connectors in the glow plug feed or sense circuitlikely
- Corroded or loose glow plug terminals, power feed connections or earth pointslikely
- Faulty glow plug control module or relaypossible
- Low battery voltage or a weak charging system causing implausible sense readingspossible
- Blown fuse or fusible link in the glow plug supplypossible
- Fault inside the engine control unit or outdated software that misreads the sense signalrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting engine temperature, battery voltage and whether other glow plug codes are present.
- Check battery condition and charging voltage, as low voltage can cause false glow plug circuit faults.
- Visually inspect the glow plug wiring, connectors, module and fuses for heat damage, chafing, corrosion or water ingress.
- Check the glow plug supply fuse or fusible link and the relevant relay for continuity and correct operation.
- Check the power feed and earth connections at the glow plug module and the glow plug terminals for tightness and corrosion.
- Measure the resistance of each glow plug against the manufacturer's specification, and check for shorts to earth.
- Using a scan tool with live data or an activation test, command the glow plugs and check that the current draw or sense signal matches specification, following the manufacturer's procedure for the engine.
- Check for technical service bulletins or software updates for the vehicle, and test the control module only after the wiring and plugs are proven good.
How to fix
- Replace any glow plug that is out of specification, taking care to follow the correct removal procedure to avoid snapping seized plugs.
- Repair or replace damaged wiring, connectors and terminals, and clean and tighten power and earth connections.
- Replace a blown fuse only after finding and correcting the cause of the overload.
- Replace a faulty glow plug relay or control module, and code or adapt it as the manufacturer requires.
- Restore battery and charging system health if voltage is low.
- Update the control unit software only where the manufacturer lists an outdated calibration as a known cause.
Can I keep driving?
The car can usually be driven, but cold starting may be hard and the engine may run roughly until warm. Book it in soon, especially before cold weather, and do not keep cranking the engine if it struggles to start.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.