Failed cylinder 8 glow plug (open or shorted internally); Damaged or corroded electrical connector at the glow plug; Chafed or broken wire in the glow plug control circuit (short to ground); Faulty glow plug control module (GPCM) or relay; Poor ground connection for the glow plug circuit; PCM internal driver failure (rare)

DTC codes / P06xx · Computer and output circuits / P068E

P068ECylinder 8 Glow Plug Control Circuit Low

Q: What does code P068E mean?

Cylinder 8 Glow Plug Control Circuit Low. P068E indicates that the powertrain control module (PCM) has detected an abnormally low voltage or current on the control circuit for cylinder 8's glow plug, which is used in diesel engines to warm the combustion chamber for reliable cold starts. The PCM monitors the circuit and sets this code when the signal falls below the expected threshold, typically indicating a short to ground, a failed glow plug, or a wiring fault.

P068E indicates that the powertrain control module (PCM) has detected an abnormally low voltage or current on the control circuit for cylinder 8's glow plug, which is used in diesel engines to warm the combustion chamber for reliable cold starts. The PCM monitors the circuit and sets this code when the signal falls below the expected threshold, typically indicating a short to ground, a failed glow plug, or a wiring fault.

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
Excessive white smoke from the exhaust after a cold start
Engine misfire or stumbling during the first few minutes of operation
Reduced fuel economy and increased emissions during warm-up
In severe cases, the engine may fail to start in cold weather

Common causes, most likely first

Failed cylinder 8 glow plug (open or shorted internally)
Damaged or corroded electrical connector at the glow plug
Chafed or broken wire in the glow plug control circuit (short to ground)
Faulty glow plug control module (GPCM) or relay
Poor ground connection for the glow plug circuit
PCM internal driver failure (rare)

How to diagnose and fix it

Scan all modules for related codes and record freeze-frame data to confirm the fault conditions
Visually inspect the cylinder 8 glow plug, its connector, and the wiring harness for damage or corrosion
Measure the resistance of the glow plug with a multimeter and compare to specifications (typically 0.5–2 ohms)
Check for voltage and ground signals at the glow plug connector during the glow plug pre-heat cycle using a multimeter or oscilloscope
Test the glow plug control module or relay according to the manufacturer's procedure
Repair or replace any damaged wiring, connectors, or the glow plug as needed
Clear the code and verify the repair by performing a cold start and monitoring live data

Glow plug circuit low-voltage traps

A low-voltage code on a glow plug circuit often results from a short to ground in the harness rather than a failed glow plug, so always inspect the wiring before replacing parts.
The glow plug control module may set this code if the glow plug resistance is out of specification, even if the plug still heats; resistance testing is more reliable than a visual check.
On some vehicles, a weak battery or poor charging system can cause low voltage on the glow plug circuit and trigger this code, so check battery health first.
Cylinder 8 glow plug failure can be caused by oil or coolant contamination in the connector, which may indicate a larger engine issue such as a leaking injector seal or head gasket.
This code does not always mean the glow plug itself is faulty; the PCM driver circuit or a shared ground point can be the root cause, especially if multiple glow plug codes are present.

Can I keep driving with P068E?

You can usually drive the vehicle with this code, but cold starting may be difficult and the engine may run rough until warm; avoid heavy loads and cold starts until repaired, and address it promptly to prevent further damage to the glow plug system or catalytic converter from unburned fuel.

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.