U0305: Software Incompatibility With Cruise Control Module
What to do
Assume the automatic emergency braking has gone too, and leave more room than usual.
That is the important part. Cruise control refusing to work is an inconvenience — but on most modern cars the same system is what warns you about a collision and brakes for one, and losing that is not something you will notice until you need it.
Nothing is broken. This code means two of the car's computers are running software that does not belong together, and it is a programming job rather than a repair.
One question worth asking yourself: did this appear overnight, with nothing done to the car? Many cars now update their driver assistance software over the air, and an update that only partly completed — or that was interrupted by the car being switched off part-way — leaves exactly this. If so, the fix is completing the update, and it may be free.
Otherwise mention any recent module replacement, dealer visit or recall work.
What this code means
A module is running software that does not belong with the cruise control module's. See U0300 for the family and U0301 for why the named module is not the accused.
Cruise control has changed enough in a decade to make this code mean two quite different things, and establishing which the vehicle has is the first step.
On a conventional system the module simply holds a set speed, and a mismatch is an inconvenience: cruise control refuses to engage and nothing else changes.
On an adaptive system it is part of the driver assistance chain, and its software has to agree with the radar or camera at U0433, the brake system at U0318 and the engine's torque interface. A mismatch there disables the whole chain, so automatic emergency braking is very often unavailable alongside it — and that is a system the driver is unlikely to notice missing until the moment it would have acted.
So the practical instruction is to establish what has actually gone. If the vehicle normally warns of a collision or brakes for one, assume it no longer does, and drive with the margin that implies.
Where the fault comes from has one cause specific to this family, and it is worth naming because it is becoming common. Driver assistance systems receive over-the-air software updates on many vehicles, and an update that reached the assistance modules but not the engine or brake modules — or one that was interrupted by the vehicle being switched off — leaves exactly this. A code that appeared overnight with no work done is that, and the remedy is completing the update rather than diagnosing hardware.
Likely causes
Start here
- Software updated on one module only · specialist
- Interrupted module programming · specialist
- Software calibration out of date · specialist
Less common
- Incorrect module configuration after replacement · specialist
- Second hand module locked to another vehicle · specialist
- Module not coded to the vehicle · 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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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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