U0315: Software Incompatibility With Anti-Lock Brake System (ABS) Control Module
What to do
Your brakes still work normally. That is the first thing to know.
The anti-lock system releases brake pressure you have already applied — it cannot apply any of its own — so with it unavailable the car stops exactly as it always did. What you lose is the protection against a wheel locking in an emergency stop or on a wet or icy road. Drive accordingly, leave more room, and get it sorted.
Expect stability control to be off as well, since it is built on top of the same module.
Nothing is broken. This code means two computers are running software that does not belong together — a programming job rather than a repair.
One check is worth doing yourself, and it may reveal more than you expect. Compare your speedometer with a satellite speed reading from a phone. The ABS computer holds your car's wheel and tyre size, and it is where most of the car gets its road speed from — the speedometer, the odometer, the cruise control, the gearbox. A module configured for a different tyre size reports a speed that is wrong by a few per cent and completely believable, so nothing rejects it and everything quietly follows it.
If the speedometer is out, say so — it confirms the problem is configuration rather than hardware, and it points straight at the fix.
Do not let the ABS hydraulic unit be replaced on the strength of this. It is an expensive part, and a second-hand one is the commonest way cars end up here in the first place.
What this code means
A module is running software that does not belong with the anti-lock braking module's. See U0300 for the family and U0301 for why the named module is not the accused.
The reassurance comes first, and it is the same one as at U0121: the brakes still work. An anti-lock system releases pressure the driver has already applied; it cannot apply any of its own. So a vehicle with this code stops normally, and the loss is the ability to prevent a wheel locking under heavy braking — which matters in an emergency and on a poor surface, and not at all on the way to a garage.
What makes this code more consequential than its neighbours is what an ABS module's software actually holds, and it reaches well beyond braking.
It carries the vehicle's variant configuration: wheel and tyre size, axle ratios, whether the vehicle has stability control, traction control, hill hold, trailer stability assist, an electric park brake, a diesel or petrol engine. And it holds the constant that turns wheel rotation into road speed.
That last one is why a mismatch here corrupts things that look unrelated. The ABS module is the road speed source for most of the vehicle — the speedometer, the odometer, cruise control, speed-dependent steering assist and volume, the transmission's shift schedule. A module carrying another variant's tyre size reports a speed that is wrong by a few per cent and entirely plausible, so nothing rejects it and everything downstream is quietly and consistently off.
So the check worth doing is to compare the speedometer against a satellite reading. A discrepancy confirms a variant mismatch immediately and points the repair at configuration rather than hardware.
And expect stability control to be unavailable, since it is built on top of this module and will not run on a foundation it cannot verify.
A hydraulic unit is an expensive part and this is not a reason to fit one. A second-hand ABS module is the classic route into this code, and it needs coding to this vehicle's variant regardless of how well the part number matches.
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
- Module not coded to the vehicle · specialist
Less common
- Interrupted module programming · specialist
- Software calibration out of date · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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 you measured, not only what you replaced.
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