Damaged, corroded or loose wiring or connectors between the PCM and the glow plug control module; Poor power or earth supply to the glow plug control module, including a blown fuse or relay fault; Low battery voltage or a weak charging system causing communication dropouts; Faulty glow plug control module; Water ingress or heat damage at the glow plug module or its connector; Faulty PCM or outdated PCM software, where a known issue exists for that model; Shorted glow plug or wiring fault pulling down the module supply and disrupting its output.

P0683

Glow Plug Control Module 1 to PCM Communication Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

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

What it means

P0683 means the powertrain control module (PCM) has detected a fault in the communication circuit between itself and the glow plug control module on a diesel engine. The PCM expects valid data or a correct feedback signal from the glow plug module and has seen it missing, out of range or corrupted. The exact wiring and communication type (dedicated feedback line or data bus) varies by make and model.

Symptoms

Glow plug warning lamp on or flashing
Engine management light on
Hard starting in cold weather
White smoke and rough running on a cold start
Extended cranking before the engine fires
Glow plugs not operating or operating continuously

Possible causes

Damaged, corroded or loose wiring or connectors between the PCM and the glow plug control modulelikely
Poor power or earth supply to the glow plug control module, including a blown fuse or relay faultlikely
Low battery voltage or a weak charging system causing communication dropoutspossible
Faulty glow plug control modulepossible
Water ingress or heat damage at the glow plug module or its connectorpossible
Faulty PCM or outdated PCM software, where a known issue exists for that modelrare
Shorted glow plug or wiring fault pulling down the module supply and disrupting its outputrare

How to diagnose

Read all stored and pending codes and freeze frame data, noting battery voltage and engine temperature when the fault set
Check battery condition and charging voltage, as low voltage can cause communication faults
Visually inspect the glow plug module, its connectors and the wiring for corrosion, chafing, heat damage and water ingress
Check the relevant fuses and relays and the power and earth supplies to the glow plug module against the wiring diagram
Test the communication or feedback circuit between the PCM and the module for open circuit, short to earth, short to supply and high resistance
Using a scan tool, check whether the glow plug module responds and whether live data or an output test is available for that model
Check the glow plugs and their wiring for shorts or abnormal current draw
Check for manufacturer software updates or technical bulletins for the PCM and glow plug module on that model

How to fix

Repair or replace damaged wiring and clean or replace corroded connectors
Restore correct power and earth supply, replacing faulty fuses or relays as needed
Charge or replace a weak battery and rectify any charging system fault
Replace the glow plug control module if it is confirmed faulty, then carry out any coding or adaptation the manufacturer requires
Replace any shorted glow plugs found to be overloading the circuit
Update or reflash the PCM software only where an outdated calibration is a known cause for that model, or repair or replace the PCM if confirmed faulty

Can I keep driving?

Medium severity

The car can usually be driven, but cold starting may be poor and it may run roughly until warm. Have it repaired soon, as starting may become unreliable and a continuing fault could affect emissions and engine running.

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