Cylinder 2 glow plug control wiring shorted to voltage or damaged insulation; Corrosion, damaged pins or poor connection at the glow plug connector or control module plug; Faulty cylinder 2 glow plug with internal fault affecting the circuit; Faulty glow plug control module or driver stage; Wiring harness chafed against engine components, causing a short to a power feed; Fault in the engine control unit itself or a software issue where an outdated calibration is a known cause for the model.

P066D

Cylinder 2 Glow Plug Control Circuit High.

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
6D: FaultThe specific fault in that area

What it means

P066D means the engine control unit has detected a high voltage or short to voltage fault in the control circuit for the cylinder 2 glow plug. The control unit monitors the circuit for the expected electrical state when it switches the glow plug on and off, and the reading did not match. Glow plug control layout varies by model and engine, so the exact circuit design should be checked for the vehicle.

Symptoms

Engine management or glow plug warning light on
Hard starting or extended cranking, especially when cold
White smoke on cold start-up
Rough running or misfire on cold start that clears as the engine warms
Increased cold-start emissions or noticeable diesel knock until warm

Possible causes

Cylinder 2 glow plug control wiring shorted to voltage or damaged insulationlikely
Corrosion, damaged pins or poor connection at the glow plug connector or control module pluglikely
Faulty cylinder 2 glow plug with internal fault affecting the circuitpossible
Faulty glow plug control module or driver stagepossible
Wiring harness chafed against engine components, causing a short to a power feedpossible
Fault in the engine control unit itself or a software issue where an outdated calibration is a known cause for the modelrare

How to diagnose

Read all stored codes and freeze frame data, noting engine temperature, battery voltage and whether other glow plug codes are present
Visually inspect the glow plug wiring and connectors at cylinder 2 and at the control module for chafing, melting, corrosion or water ingress
Check battery condition and charging voltage, as low or unstable voltage can upset circuit monitoring
Measure the resistance of the cylinder 2 glow plug and compare it with the manufacturer specification
Check the control wire between the module and cylinder 2 for a short to voltage with the connectors disconnected, following the wiring diagram for the vehicle
Use a scan tool with live data or actuator tests to command the glow plugs and observe the cylinder 2 circuit response and current draw if supported
Check the glow plug control module power and earth supplies and look for any manufacturer service bulletins or calibration updates for the model

How to fix

Repair or replace damaged wiring and secure the harness away from heat and sharp edges
Clean or replace corroded or damaged connectors and terminals
Replace the cylinder 2 glow plug if it is out of specification, using the correct type for the engine
Replace the glow plug control module if the circuit and plug are proven good and the driver fault is confirmed
Apply a manufacturer calibration update only if an outdated calibration is a documented cause for the vehicle, then clear the code and retest

Can I keep driving?

Low severity

The car can normally be driven, but cold starting may be poor and the fault should be fixed before winter. Book it in soon, and avoid repeated long cranking attempts.

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