U0122: Lost Communication With Vehicle Dynamics Control Module
What to do
The car will drive completely normally, which is the trap. Stability control does nothing at all until the car starts to slide, so its absence is invisible until the moment you need it.
What it does when working: it notices that the car is going somewhere other than where you are steering, and corrects it by braking individual wheels and cutting engine power — faster and more precisely than anyone can react. Without it, a slide that would have been caught silently is now yours to catch.
Drive with that in mind, particularly in rain, on ice, on loose surfaces and through fast corners. Slow down earlier, and be gentler with the steering and the throttle. Traction control has almost certainly gone with it, so wheelspin pulling away on a wet or gravelly surface is also unmanaged now.
Get it looked at rather than living with the lamp — and note that as with all network codes, the module itself is often innocent. Its power, earth and the bus wiring come first.
What this code means
The vehicle dynamics — stability control — module has stopped being heard from. The general reasoning is at U0100.
Stability control and anti-lock braking are commonly confused and do different jobs. Anti-lock braking stops a wheel locking while the driver is braking. Stability control acts when the car is going somewhere other than where it is pointed, and it acts whether or not the driver is braking at all — comparing where the steering wheel says the driver wants to go against what the yaw rate and acceleration sensors say the car is actually doing, and correcting the difference.
It has two tools, and one of them is the subject of codes already in this corpus. It can brake an individual wheel to generate a turning moment, and it can ask the engine for less torque — which is the request line described at P2544 and answered at P2637. So a vehicle with this module silent has lost the fastest intervention available to it, and the torque management conversation those codes describe has nothing at the other end.
The characteristic of this fault is that nothing changes until something does. The car drives entirely normally in every ordinary situation, because stability control does nothing at all until the vehicle starts to depart from the driver's intention. A capability that only exists in an emergency has gone, and the only notice is a lamp on the dashboard.
That is worth saying plainly, because the natural response to a warning lamp on a car that drives perfectly is to leave it. Here, driving perfectly is exactly what a car with no stability control does right up until the moment it needed some.
Likely causes
Start here
- Failed power or earth supply to the module · moderate
- Damaged data bus wiring · moderate
- Corroded or loose connector · easy
- Blown fuse or failed supply · easy
Less common
- Another module holding the bus down · specialist
- Faulty stability control module · 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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