What it means
The diagnostic feedback line that monitors glow plug current draw reports a general electrical fault — open, shorted, or out of plausibility. Used to verify each plug actually heats up.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The glow plug sense circuit reports feedback about current draw so the control module can judge whether the glow plugs are heating as commanded. P037D sets when that feedback is missing, electrically faulty, or implausible, without specifying a low or high signal condition.
Common causes
Most likely first.
- Glow-plug current-sensing circuit wiring open or shorted
- Loose or corroded connector
- Failed current-sensing module or control unit
- Fault in a glow plug affecting the monitored current signal
Symptoms
- Glow plug warning light on (often orange coil symbol)
- Hard cold start or no start in cold weather
- White smoke from exhaust during warm-up
How to diagnose it
- Record freeze-frame data and compare the glow plug command with available sense or current feedback during a cold-start cycle.
- Inspect the sense-circuit wiring and connectors between the glow plug system and its sensing or control module for opens, shorts, corrosion, or loose pins.
- Check whether the glow plug warning lamp and cold-start symptoms match the reported feedback fault.
- Test sense-circuit continuity and isolation, then check each monitored glow plug for an electrical fault using the manufacturer's procedure.
- If wiring and plugs pass, test the current-sensing module and control unit against the manufacturer's specification.
Common fixes
- Repair an open, shorted, or damaged section of the glow plug sense wiring.
- Clean or repair loose or corroded sense-circuit connector terminals.
- Replace a failed glow plug that is disrupting the monitored current signal.
- Replace the current-sensing module or control unit if tests confirm it is faulty.
Can I keep driving?
Glow plug heating may be reduced or unverified, which can make cold starts difficult and cause white smoke during warm-up. Avoid repeated long cranking in cold weather.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.