Faulty cylinder 3 glow plug with an internal short to earth; Wiring to the cylinder 3 glow plug chafed or shorted to earth; Corroded or damaged connector or terminal at the glow plug or control module; Faulty glow plug control module or driver stage; Water ingress or carbon tracking at the glow plug connection; Fault within the engine control unit itself.

P066E

Cylinder 3 Glow Plug Control Circuit Low.

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
6E: FaultThe specific fault in that area

What it means

P066E means the engine control unit has detected a low voltage or low signal state in the control circuit for the cylinder 3 glow plug. The unit monitors the glow plug driver output, and the signal was lower than expected, which usually points to a short to earth or a fault in the driver or wiring. It applies to diesel engines with individually controlled glow plugs, and the exact circuit layout depends on the model and engine.

Symptoms

Engine management light on
Hard or extended cranking on cold starts
Rough running or white smoke after a cold start
Glow plug warning light flashing or staying on (varies by model)
Higher emissions or poor cold-running performance
Other glow plug circuit codes stored alongside

Possible causes

Faulty cylinder 3 glow plug with an internal short to earthlikely
Wiring to the cylinder 3 glow plug chafed or shorted to earthlikely
Corroded or damaged connector or terminal at the glow plug or control modulepossible
Faulty glow plug control module or driver stagepossible
Water ingress or carbon tracking at the glow plug connectionpossible
Fault within the engine control unit itselfrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including engine temperature and battery voltage
Check for other glow plug codes, as a pattern across cylinders suggests a module or supply fault rather than a single plug
Visually inspect the cylinder 3 glow plug wiring and connectors for chafing, heat damage, corrosion or moisture
Check battery condition and charging voltage, as low voltage can upset glow plug diagnostics
Measure the cylinder 3 glow plug resistance and compare it with the manufacturer's specification
Test the control wire for a short to earth with the connector unplugged, following the wiring diagram for that model
Check the glow plug control module supply, earth and output signals as per the manufacturer's procedure
Clear the code and retest from cold to see whether it returns

How to fix

Replace the cylinder 3 glow plug if it is out of specification or shorted
Repair or replace damaged wiring between the control module and the cylinder 3 glow plug
Clean or renew corroded connectors and terminals, and seal against moisture
Replace the glow plug control module if the driver output is faulty and the wiring and plug test correctly
Check for an updated calibration only if the manufacturer lists a known software fault for this code on that engine

Can I keep driving?

Low severity

The car can usually be driven, but cold starting may be harder and emissions may be higher. Book it in soon, especially before cold weather, and avoid repeated long cranking.

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