What Does P0674 Mean?
The PCM has detected a malfunction in the cylinder 4 glow plug circuit on a diesel engine. The glow plug or its wiring is not operating within the expected electrical parameters. Without proper glow plug function, cylinder 4 will not combust fuel efficiently during cold starts. The driver will notice harder starting in cold weather, brief rough running during warm-up, and white exhaust smoke until the engine reaches operating temperature.
Common Causes
40%
Failed cylinder 4 glow plug (open or degraded)
25%
Corroded or loose bus bar connection at cylinder 4
20%
Wiring fault in the cylinder 4 glow plug circuit
10%
Glow plug control module cylinder 4 output failure
5%
Glow plug tip swollen or broken inside combustion chamber
Diagnostic Steps
1
Disconnect the cylinder 4 glow plug and measure resistance — spec is 0.5-2.0 ohms. Compare to other cylinders for reference. Out-of-spec readings confirm a failed plug.
2
Verify power supply at the cylinder 4 bus bar or connector during the glow cycle. Battery voltage should be present for the programmed glow duration.
3
Inspect the bus bar connection at cylinder 4 — on 4-cylinder diesels this is the last plug in the chain and bus bar corrosion/looseness is common at the end.
4
If the plug tests bad, try removal carefully. Apply penetrating oil the night before and warm the engine to operating temperature. Use a proper glow plug socket with a torque limiter.
5
After installation of a new glow plug, torque to spec (typically 10-15 Nm — do not over-torque), clear the code, and verify by monitoring glow plug current during a cold start cycle.
Estimated Repair Cost
$60 - $350
Parts + labor, varies by vehicle and location
The PCM has detected a malfunction in the cylinder 4 glow plug circuit on a diesel engine. The glow plug or its wiring is not operating within the expected electrical parameters. Without proper glow plug function, cylinder 4 will not combust fuel efficiently during cold starts. The driver will notic...
The most common cause of P0674 (Cylinder 4 Glow Plug Circuit) is: Failed cylinder 4 glow plug (open or degraded)
Typical repair costs for P0674 range from $60 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Not an immediate safety issue. Cold-start quality will be reduced, and on 4-cylinder diesels, having one glow plug out of four non-functional is a 25% loss — this is more noticeable than on 6 or 8-cylinder engines. In extreme cold, the engine may fail to start. Repair promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0674 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Glow Plug System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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