Short to voltage or damage in the glow plug sense or feedback wiring; Corroded, loose or damaged connector at the glow plug control module or glow plugs; Faulty glow plug control module with an internal fault in its sense circuit or output driver; Failed glow plug or plugs giving an abnormal voltage or current reading, such as an open circuit; Poor earth or supply voltage fault affecting the module's reference readings; Fault in the engine control unit or its software or calibration, where the manufacturer lists it as a known cause.

P037F

Glow Plug Sense Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
3: AreaIgnition system or misfire
7F: FaultThe specific fault in that area

What it means

P037F means the engine or glow plug control unit has seen a voltage on the glow plug sense (feedback) circuit that is higher than expected. The sense circuit is how the control unit monitors glow plug voltage or current. The exact circuit layout, and whether it covers all plugs or one bank, depends on the engine and model.

Symptoms

Malfunction indicator lamp or glow plug warning lamp on
Longer cranking or hard starting, especially when cold
White or grey smoke and rough running just after a cold start
Glow plug lamp behaving oddly (staying on, not lighting or flashing)
Increased emissions or poor idle until the engine warms up
No obvious symptoms in warm weather

Possible causes

Short to voltage or damage in the glow plug sense or feedback wiringlikely
Corroded, loose or damaged connector at the glow plug control module or glow plugslikely
Faulty glow plug control module with an internal fault in its sense circuit or output driverpossible
Failed glow plug or plugs giving an abnormal voltage or current reading, such as an open circuitpossible
Poor earth or supply voltage fault affecting the module's reference readingspossible
Fault in the engine control unit or its software or calibration, where the manufacturer lists it as a known causerare

How to diagnose

Read all stored and pending codes and note the freeze frame data (coolant temperature, battery voltage, engine state), then look for related glow plug or module codes.
Check the battery condition and charging voltage, as low or unstable voltage can upset glow plug diagnostics.
Visually inspect the glow plug wiring, connectors and the control module for heat damage, chafing, corrosion, water ingress and rodent damage.
Check the relevant fuses and relays against the wiring diagram for the model.
With the ignition on, use the live data to check the glow plug command and feedback values against specification, if the vehicle supports it.
Test the sense circuit wiring for a short to supply voltage and for resistance against the wiring diagram, with the connectors disconnected.
Measure the resistance and current draw of each glow plug against the manufacturer's figures, replacing any out of range.
Check the module's supply and earth connections, then test or substitute the module only once the wiring and plugs have been proved good.

How to fix

Repair or replace damaged wiring and any short to voltage on the sense circuit.
Clean, repair or replace corroded or damaged connectors and terminals.
Replace any faulty glow plugs, usually as a full set if they are old, following the correct torque procedure.
Repair poor supply or earth connections found during testing.
Replace the glow plug control module if it is confirmed faulty, and carry out any adaptation the manufacturer requires.
Apply a manufacturer software update only if an outdated calibration is a documented cause for the vehicle.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but cold starts may be hard and emissions may be higher. Get it checked soon, as a failing glow plug system can strain the starter and battery and may lead to further faults.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.