Failed cylinder 8 glow plug (open element or internal short); Damaged or corroded electrical connector at the glow plug; Open or shorted glow plug control circuit wiring (including chafed insulation or broken wire); Faulty glow plug control module (GPCM) or relay, if the vehicle uses one; Poor ground connection for the glow plug circuit; ECM internal driver fault (less common)

DTC codes / P06xx · Computer and output circuits / P068F

P068FCylinder 8 Glow Plug Control Circuit High

Q: What does code P068F mean?

Cylinder 8 Glow Plug Control Circuit High. P068F means the engine control module (ECM) has detected an abnormally high voltage on the control circuit for cylinder 8's glow plug, which is used on diesel engines to warm the combustion chamber for cold starts. The ECM commands the glow plug on and monitors the circuit; a high voltage reading indicates the circuit is open, shorted to voltage, or the glow plug itself has failed in a way that prevents current flow.

P068F means the engine control module (ECM) has detected an abnormally high voltage on the control circuit for cylinder 8's glow plug, which is used on diesel engines to warm the combustion chamber for cold starts. The ECM commands the glow plug on and monitors the circuit; a high voltage reading indicates the circuit is open, shorted to voltage, or the glow plug itself has failed in a way that prevents current flow.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Hard starting or rough idle when the engine is cold, especially in low temperatures
Excessive white smoke from the exhaust after a cold start
Misfire or rough running during the warm-up period
Reduced fuel economy during cold operation
In rare cases, a no-start condition in very cold weather

Common causes, most likely first

Failed cylinder 8 glow plug (open element or internal short)
Damaged or corroded electrical connector at the glow plug
Open or shorted glow plug control circuit wiring (including chafed insulation or broken wire)
Faulty glow plug control module (GPCM) or relay, if the vehicle uses one
Poor ground connection for the glow plug circuit
ECM internal driver fault (less common)

How to diagnose and fix it

Scan all modules for stored codes and freeze-frame data to confirm P068F is the only glow plug code
Inspect the cylinder 8 glow plug connector and wiring for corrosion, damage, or loose pins
Measure the resistance of the cylinder 8 glow plug with a multimeter and compare to specification (typically 0.5–2 ohms)
Check for voltage on the control circuit with the key on and engine off; a high voltage with the glow plug disconnected suggests a short to voltage
Test the glow plug control module output and ground circuit integrity using a test light or oscilloscope
If the glow plug tests bad, replace it and clear the code; if the circuit tests bad, repair the wiring or replace the control module
After repair, clear codes and perform a cold-start test to verify the glow plug activates and the code does not return

Glow plug circuit high voltage traps

A high voltage code often means the glow plug has failed open, so the ECM sees full system voltage on the control side because no current flows through the plug.
Corrosion inside the glow plug connector can create enough resistance to set a high voltage code without any visible damage to the wiring harness.
On vehicles with a glow plug control module, a failed module can set a high voltage code for a single cylinder even when the glow plug itself is good.
The ECM may set P068F intermittently if the glow plug only fails when cold, so always test the circuit when the engine is at ambient temperature.
Do not overlook a poor engine ground; a bad ground can cause the ECM to see incorrect voltage on the glow plug control circuit.

Can I keep driving with P068F?

You can usually drive with P068F, but cold starting may be difficult and the engine may run rough until warm. Avoid heavy load or high-speed driving until the fault is repaired, and address it before winter weather arrives.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.