Failed glow plug on cylinder 7 (open-circuit heating element); Corroded, loose or damaged connector or terminal at the cylinder 7 glow plug; Damaged, chafed or broken wiring between the glow plug and the control module; Poor power or earth supply to the glow plug circuit, such as a corroded connection or blown fuse; Fault in the glow plug control module or its output driver for cylinder 7; Fault in the engine control unit or outdated software, depending on the model.

P0677

Cylinder 7 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
77: FaultThe specific fault in that area

What it means

P0677 is the generic code for an open circuit or fault in the glow plug circuit for cylinder 7. The engine control unit (or glow plug control module) monitors the current or voltage in each glow plug circuit and has found that cylinder 7 does not match what it expects, typically no current flow. This only applies to diesel engines with at least seven cylinders, and the circuit layout varies by model and engine.

Symptoms

Glow plug warning light or engine management light on
Harder starting when the engine is cold
Rough running or misfire on start-up in cold weather
White smoke from the exhaust on cold starts
Higher fuel consumption or noisy running until the engine warms up
Possibly reduced power if the car has entered a protective mode

Possible causes

Failed glow plug on cylinder 7 (open-circuit heating element)likely
Corroded, loose or damaged connector or terminal at the cylinder 7 glow pluglikely
Damaged, chafed or broken wiring between the glow plug and the control modulepossible
Poor power or earth supply to the glow plug circuit, such as a corroded connection or blown fusepossible
Fault in the glow plug control module or its output driver for cylinder 7possible
Fault in the engine control unit or outdated software, depending on the modelrare

How to diagnose

Read all stored and pending codes and the freeze frame data, and note whether other glow plug codes are present.
Check for relevant technical service bulletins or known issues for the specific model and engine.
Visually inspect the cylinder 7 glow plug connector, terminal and wiring for corrosion, heat damage, chafing or looseness.
Check the fuses and relays in the glow plug supply, and the power and earth connections at the control module.
Measure the glow plug resistance with the engine cold and compare it with the manufacturer's specification. An open circuit reading confirms a failed plug.
Test the wiring for continuity, short circuits and voltage drop between the module and the glow plug, following the wiring diagram for the vehicle.
Use live data or an actuator test, where supported, to check that the module commands and drives the cylinder 7 output.
If the plug and wiring are good, check the control module output and software status as the manufacturer specifies.

How to fix

Replace the faulty cylinder 7 glow plug, using the correct specification and tightening to the manufacturer's torque.
Clean or replace the corroded or damaged connector and terminal.
Repair or replace the damaged wiring section.
Restore the power or earth supply, or replace the blown fuse after finding out why it failed.
Replace or repair the glow plug control module if it is confirmed faulty.
Update the control unit software only if the manufacturer lists an outdated calibration as a known cause.

Can I keep driving?

Low severity

The car can usually be driven, as one glow plug out of circuit mainly affects cold starting and cold running. Book it in soon, especially before cold weather, and take care when removing seized glow plugs, as they can snap.

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