Network code
U0121: Lost communication with ABS module
How this range is built
| Part of the job | Low | High |
|---|---|---|
| Parts | $5 | $150 |
| Labor: 1.5 to 6 hours × $125 to $175 an hour | $188 | $1,050 |
| Fees: shop supplies, disposal, diagnostics | $0 | $60 |
| Total, rounded | $190 | $1,275 |
The hourly rate is the BLS Occupational Employment and Wage Statistics, May 2025 average pay for this trade in Boston, $31.54 an hour, times 4 to 5.5 to cover what a shop bills (overhead, tools, insurance, profit). Parts are a band from budget aftermarket to the manufacturer part. Full method.
Not a repair shop, estimates only. Typical range, estimate. Not a quote. Your car, parts and shop change the number.
This is the range for the most common fix, can bus wiring repair. Which repair your car needs depends on a proper diagnosis.
Other modules in the car cannot talk to the ABS module. That is the usual meaning, but it varies by make, so check the scan tool or manual. A blown ABS fuse, a weak battery, a bad ground, a damaged wire or the ABS module itself can all cause it.
- Safe to drive?
- Short trips only
- Most common cause
- Blown ABS fuse
Normal brakes usually still work, but without ABS help the wheels can lock in a hard stop, so leave extra room and brake early.
What you may notice
- ABS light on
- Traction control light on
- Stability control off
- Brake warning light on some cars
Common causes, most likely first
- Blown ABS fuse
- Weak battery or ground
- Damaged wiring or connector
- Failed ABS module
- CAN network fault
Check this first
Check the ABS fuses and the battery first, then look at the connector at the ABS unit for corrosion, a loose latch or signs of water. A fuse or a connector problem is much cheaper to fix than a new module.
Other repairs that sometimes fix U0121
| Repair | Typical range, Boston |
|---|---|
| ABS control module repair or replacement | $550 to $1,775 |
| Battery replacement | $150 to $490 |
| Diagnostic scan (check engine light) | $60 to $290 |
Before you pay
- Ask the shop what test showed this part is the cause, not just that the code appeared.
- Ask for parts and labor listed separately, and for the hours.
- Ask for a written OK before any extra work. Massachusetts rules require written authorization before repairs.
Got a quote already? Check it against the range. Want to see if your car has a recall tied to this problem? Check recalls by VIN.
Need to read a code yourself? OBD-II scanners on eBay (affiliate link, disclosure).
U0121 questions
Is the ABS module bad?
Not always. Fuses and wiring are checked first, because they are cheaper and more common. Replacing the module without those checks can mean paying for a part that was not the problem.
Will the brakes work?
Normal brakes usually work, without anti-lock help. Drive carefully on wet or icy roads, leave extra stopping distance, and get the system checked soon so the safety features come back.
Why other lights?
Stability and traction control rely on ABS data. When the ABS module drops off the network, those systems lose their input and shut down too, which lights up several warnings.
How much does it cost to fix U0121?
The most common fix, can bus wiring repair, has a typical range of $190 to $1,275 in Boston. It is an estimate built from parts prices and local labor wages, not a quote. Your car and shop change it.
Related codes
- C0561: ABS system disabled or module fault
- U0100: Lost communication with engine computer
- U0073: Control module communication bus off
More network codes
Code meaning written in our own words. Some codes mean different things on different makes, so check your scan tool or manual. Not a repair shop, estimates only.