U0307: Software Incompatibility With Glow Plug Control Module 1
What to do
Try not to keep cold-starting the engine while this is stored, particularly in cold weather.
Nothing is broken. This code means two of the car's computers are running software that does not belong together — a programming job rather than a repair.
The reason not to just live with it is the glow plugs themselves. Modern ones are not simply switched on and off: they are driven at carefully controlled voltages for calculated times, and kept working for minutes after the engine starts to steady the combustion and cut white smoke. Driven at the wrong voltage or for too long, they are destroyed.
And glow plugs are one of the genuinely awkward parts to replace — a seized one can snap off in the cylinder head, which turns a modest job into a very large one. So this is worth sorting before it becomes that.
You may notice hard starting on cold mornings, white smoke for the first minute, and a rougher idle until warm.
Mention any second-hand module that has been fitted. Glow plug computers are replaced fairly often, and a used one from a different engine version is a very common cause — the plug and part number often match across engines whose glow plugs do not.
What this code means
A module is running software that does not belong with the glow plug control module's. See U0300 for the family and U0301 for why the named module is not the accused.
A glow plug module is a small, cheap unit doing a job whose timing is entirely defined in software, and that is what makes a mismatch here consequential out of proportion to the part.
Modern glow plugs are not simply switched on before starting. They are driven at controlled voltages, for durations calculated from ambient and coolant temperature, and — the part people do not expect — kept working for minutes after the engine has started, because post-heating is what stabilises combustion, cuts white smoke and helps the catalyst reach temperature.
The plugs themselves are the reason the software matters. A ceramic or low-voltage steel glow plug driven at the wrong voltage or for the wrong duration is destroyed — and glow plugs are one of the genuinely awkward parts to replace, because a seized one can shear in the cylinder head and turn a cheap job into a head removal.
So the honest advice for a mismatch here is not to keep starting the engine on it. A module pair that disagrees about the drive profile can either under-heat — hard starting, white smoke, a rough first minute — or over-drive the plugs, and the second is expensive in a way that shows up weeks later.
Where it comes from is the ordinary list, with one addition: glow plug modules are replaced fairly often, and a used one from a different engine variant is a very common route, because the connector and the part number frequently match across engines whose plugs do not.
Likely causes
Start here
- Second hand module locked to another vehicle · specialist
- Incorrect module configuration after replacement · specialist
- Software updated on one module only · specialist
Less common
- Module not coded to the vehicle · specialist
- Software calibration out of date · specialist
- Interrupted module programming · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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