Damaged, corroded or loose wiring or connectors in the glow plug control module circuit; Faulty glow plug control module; Low battery voltage, poor battery terminals or a poor earth connection to the module; Blown fuse or faulty relay supplying the glow plug system; Failed or shorted glow plugs affecting the module's diagnostic feedback (model dependent); Fault in the engine control unit or outdated software (only where the manufacturer has identified this).

P0670

Glow Plug Control Module 1 Control Circuit/Open.

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
70: FaultThe specific fault in that area

What it means

P0670 means the engine control unit has detected a fault in the control circuit of the glow plug control module, such as an open circuit or a signal outside the expected range. It sets when the command, feedback or diagnostic signal between the engine control unit and the module does not match what is expected. The exact wiring layout and whether the module is separate or built into the engine control unit varies by make, model and engine.

Symptoms

Glow plug warning light on, or engine management light on
Hard starting or extended cranking, especially when cold
White smoke and rough running on cold start
Misfire or uneven idle until the engine warms up
Increased emissions or poor cold-running performance
Engine starts normally when warm, with no obvious symptoms

Possible causes

Damaged, corroded or loose wiring or connectors in the glow plug control module circuitlikely
Faulty glow plug control modulelikely
Low battery voltage, poor battery terminals or a poor earth connection to the modulepossible
Blown fuse or faulty relay supplying the glow plug systempossible
Failed or shorted glow plugs affecting the module's diagnostic feedback (model dependent)possible
Fault in the engine control unit or outdated software (only where the manufacturer has identified this)rare

How to diagnose

Read all stored codes and freeze frame data, noting engine temperature, battery voltage and whether other glow plug or communication codes are present
Check the battery condition and charging voltage, and inspect terminals for looseness or corrosion
Check the fuses and relay for the glow plug system against the vehicle wiring diagram
Visually inspect the module, its harness and connectors for heat damage, chafing, water ingress and corrosion
Check the power supply and earth at the module connector with the ignition on, using a multimeter
Test the control signal circuit between the engine control unit and the module for continuity, short to earth and short to supply
Measure the glow plug resistance and current draw to rule out failed plugs, following the manufacturer's procedure
Check for manufacturer service bulletins or software updates relevant to the vehicle

How to fix

Repair or replace damaged wiring and clean or replace faulty connectors
Replace the glow plug control module if it fails testing
Restore good battery condition and repair poor power or earth connections
Replace blown fuses or faulty relays, after finding out why they failed
Replace failed glow plugs as a set or as advised by the manufacturer
Apply a manufacturer software update only where an outdated calibration is a known cause

Can I keep driving?

Medium severity

The car can usually be driven short-term, but cold starting may get harder and emissions may rise. Get it fixed soon, as starting problems may worsen in cold weather.

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