P064C
PowertrainGlow Plug Control Module
Most of the time this is a moderate job rather than a wallet-emptying one, but it can swing either way depending on where the fault actually lies. P064C means the ECU has spotted a problem with the glow plug control module, the little brain that decides when and how long your diesel's glow plugs preheat for cold starting. On a warm summer day you might not notice a thing. Come a frosty January morning, that's when a duff module bites you and the engine cranks forever before it catches.
ⓘ Information only. This page provides general educational information about fault code P064C. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P064C mean?
P064C is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Glow Plug Control Module.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Hard starting when cold, sometimes needing two or three cranks before it fires
- • Lumpy, unstable idle for the first minute or so until the engine warms through
- • Glow plug coil light on the dash either staying lit, flashing, or not coming on at all
- • White or grey smoke puffing out the exhaust on a cold start, clearing once it warms
- • Engine light on alongside the glow plug warning
- • A diesel knock or rattle from cold that settles down as temperature comes up
Possible causes
Causes commonly associated with P064C, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failed glow plug control module itself, the most common cause here. These modules cop a lot of heat and current cycling and eventually pack up
- 2. Corroded or chafed wiring and connectors in the glow plug loom, often down by the plugs where road salt and heat do their worst
- 3. One or more glow plugs gone open circuit, which the module then reports as a system fault
- 4. Blown fuse or a tired relay feeding the glow plug circuit
- 5. Poor earth or low battery voltage starving the module of a clean supply, common on cars that sit unused for weeks
- 6. Less often, a software glitch in the ECU or PCM that needs a reflash to clear properly
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Pull the codes and the freeze frame, then check whether anything else is logged. A module fault sitting alongside individual glow plug codes points you straight at the plugs or wiring rather than the module
- 2. Get under the bonnet and eyeball the module connector and the loom running to the plugs. Look for green corrosion, melted insulation, or a connector that's worked loose with vibration
- 3. Confirm you've got a healthy battery and a clean earth. Glow systems pull serious current, so a tired battery or corroded earth point throws these codes all on its own
- 4. Check the supply fuse and the glow relay, swapping the relay for a known-good one if you can
- 5. Resistance-test the glow plugs individually with a multimeter, you're looking for somewhere around 0.5 to 2 ohms each depending on type. Anything reading open is dead
- 6. If plugs, wiring, fuses and supply all check out, the module is the prime suspect at that point
Common questions about P064C
If I clear the code, will it stay gone? +
If the cause is a loose or corroded connector, clearing it might buy you a few starts before it trips again, usually the next cold morning when the module has to actually do some work. A failed module or a dead glow plug won't clear and stay clear. The code will be back as soon as the ECU runs its next glow cycle. Clearing it is a useful test for an intermittent wiring fault, but it fixes nothing on its own.
What's the risk if I just leave it and keep driving? +
Day to day you can usually still drive, especially once the engine's warm and the glow plugs aren't needed. The real problem is winter starting. A car that cranks for ten seconds before catching is hard on the battery, the starter motor, and the engine itself, and on a really cold morning it may not start at all, leaving you stranded. Repeated cold-starting on weak glow also dumps unburnt fuel and can foul things up over time, so it's not something to ignore for a whole season.
How quickly do I actually need to sort this? +
In mild weather there's no rush, you've got time to diagnose it properly and price up the repair. Heading into autumn or winter, treat it as a priority. The fault that barely registers in September will leave you with a non-starter in December. Budget-wise you're typically looking at low to mid three figures, with a wiring or fuse repair at an independent being the cheap end and a dealer module replacement plus coding the dear end. Get it tested before the cold sets in and you avoid the breakdown.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →