Failed glow plug on cylinder 4 (open internal element); Damaged, corroded or loose wiring or connector at the cylinder 4 glow plug; Loose or corroded glow plug power feed or earth connection; Blown fuse or faulty relay in the glow plug supply (design varies by model); Faulty glow plug control module or driver output (depends on whether the engine has a separate module); Fault in the engine control unit output stage.

P0674

Cylinder 4 Glow Plug Circuit/Open.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
74: FaultThe specific fault in that area

What it means

P0674 means the engine control unit has detected an open circuit or no current flow in the glow plug circuit for cylinder 4 on a diesel engine. The control unit monitors the glow plug feed or driver and sets the code when the current or voltage does not match what it expects during a heating cycle.

Symptoms

Hard starting or extended cranking on cold mornings
White smoke and rough running for the first minute after a cold start
Glow plug or engine warning light on the dashboard
Cylinder 4 misfire when cold that clears as the engine warms
Increased diesel knock from a cold engine

Possible causes

Failed glow plug on cylinder 4 (open internal element)likely
Damaged, corroded or loose wiring or connector at the cylinder 4 glow pluglikely
Loose or corroded glow plug power feed or earth connectionpossible
Blown fuse or faulty relay in the glow plug supply (design varies by model)possible
Faulty glow plug control module or driver output (depends on whether the engine has a separate module)possible
Fault in the engine control unit output stagerare

How to diagnose

Read all stored codes and freeze frame data, noting whether other glow plug codes are present, which would point to a shared supply or module fault.
Visually inspect the glow plug wiring, connector and any busbar at cylinder 4 for damage, heat damage, corrosion or looseness.
Check the relevant fuses and relay in the glow plug supply against the vehicle wiring diagram.
Measure the cold resistance of the cylinder 4 glow plug and compare it with the other plugs and the manufacturer specification.
Check for battery voltage at the cylinder 4 glow plug connector during a commanded heating cycle, using live data or a back-probed meter reading.
Check the earth and supply connections for voltage drop under load.
If the plug and wiring are good, test the glow plug control module output and wiring continuity back to it following the model-specific procedure.

How to fix

Replace the faulty cylinder 4 glow plug, using the correct specification and tightening to the stated torque; consider replacing the set if they are old.
Repair or replace damaged wiring, connectors or the glow plug busbar.
Clean and tighten power and earth connections.
Replace the blown fuse or faulty relay after finding out why it failed.
Replace or repair the glow plug control module if it is confirmed faulty, then clear the code and confirm it does not return.

Can I keep driving?

Low severity

The car can normally be driven, but cold starting may be poor and emissions higher until it is repaired. Book it in soon, as other weak glow plugs can cause further starting problems in cold weather.

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