P064C: Glow Plug Control Module 1
What to do
Ask for the glow plugs themselves to be tested before the control module is replaced. A plug that has gone short circuit can destroy the module's output — and a new module fitted without finding that short fails the same way.
Expect hard starting in cold weather, white smoke, and rough running for the first minute or two. On a modern diesel the glow plugs keep working after the engine starts to control emissions, so this is an emissions fault as well as a starting one.
Mention how the car behaves on a cold morning specifically, since that is when this fault shows itself.
Ask for the module's connector and earth to be inspected, as these carry heavy current and fail at the connections.
What this code means
A fault has been reported by or about the first glow plug control module.
Glow plugs are no longer simply switched on for a few seconds before cranking, and understanding what changed explains this whole family of codes. A modern glow plug control module drives each plug individually with a pulse-width-modulated supply, controlling its temperature precisely — and it keeps them running for minutes after the engine has started.
That post-start glowing is emissions work rather than starting help. It keeps combustion stable while the engine is cold, which cuts the white smoke and the unburnt hydrocarbons a cold diesel would otherwise produce. Which is why a glow plug fault is an emissions fault on a modern diesel and not merely a cold-starting inconvenience.
The module also measures each plug's resistance to work out its temperature, and reports faults per cylinder — which is where the rest of this block's glow plug codes come from.
A module fault is often the consequence of a plug rather than its own failure. A glow plug that has gone short circuit drags its driver down and can destroy it, so measure the plugs before replacing the module — otherwise the new one meets the same short.
These modules sit in a hot part of the engine bay and carry heavy current, so check the connector for heat damage and the earth for corrosion before condemning the unit.
Likely causes
Start here
- Failed glow plug · moderate
- Failed glow plug control module · moderate
- Corroded or loose connector · easy
Less common
- Blown fuse supplying the glow plug circuit · easy
- Poor sensor ground connection · moderate
Symptoms
Components involved
Information, not instruction
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