What causes fault code P037D?

• Most likely: Faulty glow plug control module/relay • Likely: Oxidized or loose connectors at the glow plug module • Possible: Wiring break or short circuit in the sense line to the ECM • Rare: Faulty Engine Control Module (ECM)

How do you fix fault code P037D?

STEP 1: Check fuses for the glow plug system and inspect connectors at the module for corrosion. STEP 2: Measure the voltage on the sense line. During activation, it should switch (typically 0V to 12V or a PWM signal depending on the system). Check continuity (should be < 1 Ohm) between the module and ECM. STEP 3: Use a diagnostic tool to perform a component test of the glow plug module. Verify that all glow plugs have the correct resistance (normally 0.5-2.0 Ohms). STEP 4: Replace the glow plug control module if wiring is intact but the signal from the module is missing.

Powertrain (Engine & Gearbox)Standard EOBD

P037D - Glow Plug Sense Circuit

Q: What does fault code P037D mean?

P037D is set when the Engine Control Module (ECM/PCM) detects an electrical abnormality in the feedback signal (sense circuit) from the glow plug control module. This circuit is used to monitor that the glow plugs are actually activated and drawing the correct current. The ECM expects a specific voltage level or PWM signal when the glow plug relay/module is active. If the signal is missing, out of range, or shorted to ground/power, the code is stored. This primarily affects cold start performance and emissions during the warm-up phase.

Q: What are the symptoms of fault code P037D?

• Check Engine Light (MIL) illuminated • Glow plug indicator flashes or does not light up • Hard to start in cold weather • Increased white smoke during cold starts • Rough idle immediately after starting

Last updated:1 February 2026

Related:Glow Plug Control Module (GPCM), Glow Plugs, Engine Control Module (ECM), Wiring Harness

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0300

Random or Multiple Cylinder Misfire Detected

P0301

Cylinder 1 Misfire Detected

P0302

Cylinder 2 Misfire Detected

P0303

Cylinder 3 Misfire Detected

Technical Description

P037D is set when the Engine Control Module (ECM/PCM) detects an electrical abnormality in the feedback signal (sense circuit) from the glow plug control module. This circuit is used to monitor that the glow plugs are actually activated and drawing the correct current. The ECM expects a specific voltage level or PWM signal when the glow plug relay/module is active. If the signal is missing, out of range, or shorted to ground/power, the code is stored. This primarily affects cold start performance and emissions during the warm-up phase.

Possible Causes

Faulty glow plug control module/relay

Oxidized or loose connectors at the glow plug module

Wiring break or short circuit in the sense line to the ECM

Faulty Engine Control Module (ECM)

Symptoms

Check Engine Light (MIL) illuminated

Glow plug indicator flashes or does not light up

Hard to start in cold weather

Increased white smoke during cold starts

Rough idle immediately after starting

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P037D - Glow Plug Sense Circuit

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P037D - Glow Plug Sense Circuit

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