Short to earth in the cylinder 2 glow plug wiring or connector; Faulty or internally shorted cylinder 2 glow plug; Corroded, damaged or water-affected connector or terminal at the glow plug or control module; Faulty glow plug control module or driver circuit (on models with a separate module); Chafed harness shorting to the engine or body; Fault within the engine control unit itself.

P066C

Cylinder 2 Glow Plug Control Circuit Low.

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
6C: FaultThe specific fault in that area

What it means

P066C means the engine control unit has detected a low voltage or excessive current condition in the glow plug control circuit for cylinder 2. The control unit monitors the circuit when it commands the glow plug on or off, and the signal did not match what it expected. This code applies to diesel engines, and the circuit layout varies by model and engine.

Symptoms

Hard starting or extended cranking on a cold engine
White smoke or rough running after a cold start
Glow plug warning light on or flashing
Engine management light on
Slightly higher emissions or a diesel knock until the engine warms up

Possible causes

Short to earth in the cylinder 2 glow plug wiring or connectorlikely
Faulty or internally shorted cylinder 2 glow pluglikely
Corroded, damaged or water-affected connector or terminal at the glow plug or control modulepossible
Faulty glow plug control module or driver circuit (on models with a separate module)possible
Chafed harness shorting to the engine or bodypossible
Fault within the engine control unit itselfrare

How to diagnose

Read all stored and pending codes and note freeze frame data, including coolant temperature and battery voltage
Check for related glow plug codes on other cylinders, which would point towards a shared module or supply fault
Visually inspect the cylinder 2 glow plug wiring, connector and terminal for chafing, heat damage, oil contamination and corrosion
Check battery condition and charging voltage, as low voltage can upset circuit monitoring
Measure the cylinder 2 glow plug resistance and compare it with the manufacturer's specification, and check for a short to earth
Check the wiring between the glow plug and the control module for continuity and shorts to earth with the circuit disconnected
Test the glow plug control module output and supply following the model-specific procedure
Clear the code and retest after repair to confirm it does not return

How to fix

Repair or replace damaged wiring or the connector in the cylinder 2 glow plug circuit
Replace the cylinder 2 glow plug if it is shorted or out of specification, and consider replacing the set if they are old
Clean or replace corroded terminals and ensure the connector is seated and sealed
Replace the glow plug control module if its output is faulty and the wiring and plug are sound
Secure and reroute the harness to prevent further chafing

Can I keep driving?

Medium severity

The car can usually be driven, but cold starting may be poor and a shorted circuit can damage the module or blow a fuse. Get it checked soon, especially before cold weather.

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