U0420: Invalid Data Received From Power Steering Control Module A
What to do
The car still steers and there is still a mechanical connection to the wheels — but the power assistance may be reduced or inconsistent, and it can change while you are driving. Expect the steering to be heavier, especially when parking.
Lane keeping and parking assistance will not work. Take care on fast roads and leave more room.
The most useful question: has anything been done to the steering or suspension recently? A wheel alignment, a steering rack, work behind the steering wheel, or suspension repairs all disturb the sensor that tells the car where straight-ahead is — and that sensor has to be re-taught its zero position afterwards. If that was skipped, the car is confidently reporting a wrong steering angle with nothing actually broken, and the fix is a calibration rather than a part.
That is worth asking about specifically before anyone quotes for a steering rack or a module, because those are among the more expensive repairs on the car and a calibration is not.
What this code means
The power steering control module is broadcasting data that cannot be accepted as true. See U0400 for the family's framing and U0419 for the effort control side.
On a vehicle with electric power steering, this module drives a motor that assists the steering directly — and what it publishes is the torque it is applying and the position of the steering.
The steering position value is the one with the widest reach, and it is worth knowing where it goes: stability control needs it to know what the driver asked for, lane keeping needs it to steer, parking assistance needs it to place the wheels, and the corpus's whole stability argument at U0416 rests on it. So an implausible steering signal disables a list of systems at once, and that list looks alarming for one cause.
The steering angle sensor is the usual origin, and it has a property worth understanding: it is calibrated, not absolute. The system learns where straight-ahead is. A vehicle that has had an alignment, a steering rack, a clockspring or suspension work, and was not re-zeroed afterwards, reports an angle that is consistently and confidently wrong — which is exactly what this code describes, on hardware that is perfectly good.
So the first question is what has been done to the steering or suspension, and re-calibration is a scan tool procedure rather than a part.
The safety consequence needs stating carefully. The steering remains mechanically connected and the car steers. Assistance may reduce or become inconsistent — see U0419 — and lane keeping and parking assistance will be unavailable. The one to be alert to is assistance changing while moving.
And a caution specific to electric steering: the motor is driven by this module, and an assistance system that cannot verify its own output is one the vehicle will limit rather than trust. Expect heavier steering, and expect it at low speed where it is most noticeable.
Likely causes
Start here
- Radar sensor not calibrated after front-end work · specialist
- Faulty steering column clockspring · moderate
- Corroded or loose connector · easy
- Damaged data bus wiring · moderate
Less common
- Failed power steering control module · specialist
- Faulty power steering pressure sensor · moderate
Symptoms
Components involved
Information, not instruction
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Community experience
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