C0521Multi-axis Acceleration Sensor Module B Range/Performance
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- Same fault type as C051C, but for a second inertial module B: its rates or accelerations lie outside what driving physics permits. No manufacturer explains C0521 publicly, and which unit is B on a given car is not documented either. A second unit is common on vehicles with automated driving, where Bosch offers IMUs up to two-fold ASIL-D and stresses redundancy. A GM patent explains what corrupts such readings: six bias terms and three mounting angles, which plant calibration only partly removes and which change over time; GM estimates them from satellite navigation data. Assistance features that rely on module B, and possibly stability control, are suspended while the code is present.
- What you may notice
- Driver assistance or ESC warning message
- Adaptive cruise or lane functions unavailable
- Module B reading not zero at standstill (scan tool)
- Likely causes
- LikelyModule B loose, tilted or bracket bent after a repair or impact
- PossibleBias of the accelerometers or gyros drifted out of tolerance
- RareDefective sensing element inside module B
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.