P0678
Generic (SAE) Basic entry
Cylinder 8 Glow Plug Circuit
Severity
Medium
Typical repair cost
60 – 500 EUR
System
Powertrain
What it means
P0678 is defined as "Cylinder 8 Glow Plug Circuit". the engine control module stores it when the monitored condition for this component or system is outside the limits programmed by the manufacturer.
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Symptoms
- Check engine light on
- Engine may not start or runs in limp mode
- Several unrelated codes stored at once
- Erratic gauge or warning light behaviour
Common causes
- Cylinder 8 Glow Plug Circuit worn, contaminated or out of calibration
- Mechanical problem in the system the sensor measures
- Air, vacuum or exhaust leak influencing the reading
- Wrong or low-quality replacement part
- Wiring resistance causing a small voltage offset
How to diagnose
- Compare the live Cylinder 8 Glow Plug Circuit reading with a known-good value or a second sensor at idle and at 2500 rpm
- Check for air, vacuum or exhaust leaks that could skew the reading
- Inspect the component for contamination and clean it if the design allows
- Verify the part number is correct for the engine
- Replace the Cylinder 8 Glow Plug Circuit if the reading remains out of specification
Frequently asked questions
Can I keep driving with P0678?
Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.
Will clearing P0678 fix it?
No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.