What C0021 means
The pump motor responds, but its current draw or run time is outside the expected range.
How the engine computer detects it
The control module suspects mechanical wear or hydraulic blockage.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
Common causes
- Pump worn, low delivery Most likely
- Hydraulic block contaminated with brake fluid debris Possible
- Sensor element aged beyond calibration window Less likely
How to diagnose C0021
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: abs pump motor, abs hydraulic block, abs control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Vehicles that report C0021 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Chevrolet Silverado 1500 | 2019 | 4 | 7k |
Counts of owner complaints to the NHTSA that mention C0021 (13 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- C
- Chassis
- 0
- Generic (SAE) code
- 021
- Specific fault
Questions drivers ask
Can I drive with code C0021?
Usually yes, carefully. Your hydraulic brakes normally keep working, but ABS, traction and stability control may be off, so the wheels can lock in a hard stop. If the red brake warning light is on, the pedal feels soft or different, or the car takes longer to stop, don't drive: have it towed.
Often reported together
Codes that owners mention in the same NHTSA complaints as C0021. They can point to a shared cause, so it's worth checking them together.
- P0606Control Module Processor4 complaints
- P25A2Brake System Control Module A Requested MIL Illumination3 complaints
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.