Failed cylinder 4 glow plug (open or shorted element); Damaged or corroded electrical connector at the cylinder 4 glow plug; Broken, chafed, or open wiring in the glow plug circuit; Faulty glow plug control module (GPCM) or relay affecting cylinder 4 output; Poor ground connection for the glow plug circuit; ECM internal driver fault for the cylinder 4 glow plug circuit (rare)

DTC codes / P06xx · Computer and output circuits / P0674

P0674Cylinder 4 Glow Plug Circuit

Q: What does code P0674 mean?

Cylinder 4 Glow Plug Circuit. P0674 indicates that the engine control module (ECM) has detected a fault in the electrical circuit for the cylinder 4 glow plug, which is used in diesel engines to warm the combustion chamber for reliable cold starts. The ECM monitors the glow plug circuit for expected current draw and voltage feedback, and when the readings fall outside the programmed range, it sets this code and typically illuminates the glow plug or check engine light.

P0674 indicates that the engine control module (ECM) has detected a fault in the electrical circuit for the cylinder 4 glow plug, which is used in diesel engines to warm the combustion chamber for reliable cold starts. The ECM monitors the glow plug circuit for expected current draw and voltage feedback, and when the readings fall outside the programmed range, it sets this code and typically illuminates the glow plug or check engine light.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

Illumination of the glow plug indicator light or check engine light on the dashboard
Hard starting or extended cranking when the engine is cold
Rough idle or misfire immediately after a cold start
White smoke from the exhaust during cold running
Often no symptoms besides the warning light, especially in mild climates

Common causes, most likely first

Failed cylinder 4 glow plug (open or shorted element)
Damaged or corroded electrical connector at the cylinder 4 glow plug
Broken, chafed, or open wiring in the glow plug circuit
Faulty glow plug control module (GPCM) or relay affecting cylinder 4 output
Poor ground connection for the glow plug circuit
ECM internal driver fault for the cylinder 4 glow plug circuit (rare)

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm the fault is current and specific to cylinder 4
Visually inspect the cylinder 4 glow plug, its connector, and the wiring harness for damage or corrosion
Measure the resistance of the cylinder 4 glow plug and compare it to the manufacturer's specification
Check for battery voltage and ground at the glow plug connector during the glow plug pre-heat cycle using a multimeter or oscilloscope
Test the glow plug control module output for cylinder 4 and verify the control signal from the ECM
Repair or replace any faulty wiring, connector, glow plug, or control module as indicated by test results
Clear the diagnostic trouble codes and perform a cold-start drive cycle to verify the repair

Glow plug circuit faults that fool technicians

A glow plug that tests good with an ohmmeter can still fail under load, so a current ramp test with a clamp or oscilloscope is more reliable than resistance alone.
Corroded terminals inside the glow plug connector often cause intermittent P0674 without any visible damage to the plug itself.
The glow plug control module may fail on only one channel, so swapping the cylinder 4 glow plug with another cylinder is a quick way to isolate the fault.
P0674 can be set by a weak battery or charging system issue that causes low voltage during the glow plug pre-heat cycle, so always check battery health first.
On some vehicles, the glow plug circuit is monitored only during a cold start, so the code may not reset until the engine is completely cold.

Can I keep driving with P0674?

You can usually drive the vehicle with P0674, but cold starting may be difficult and prolonged cranking can wear the starter and battery. Avoid heavy loads or long trips until the fault is repaired, and address the issue promptly to prevent secondary 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.