C1240 Code: ABS Pressure Differential Switch Short to Battery
🟠 Moderate severity · drivable
You can usually keep driving, but the ABS and brake warning lights may be on and anti-lock braking may not work.
What C1240 means
The ABS hydraulic pressure differential switch watches the brake pressure in the two brake circuits. This code means the switch circuit is shorted to battery power, so the ABS computer sees voltage where it does not expect any. The anti-lock brakes may be turned off, though the normal brakes usually still work.
Symptoms
- ABS warning light on the dash
- Brake warning light on
- Anti-lock braking may not engage
- Brake pedal feels normal but ABS is disabled
Common causes
- most common: Wiring in the ABS harness shorted to battery voltage
- common: Faulty pressure differential switch
- less common: Corroded or damaged ABS connector
- rare: Failed ABS control module
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Inspect the ABS wiring and fix any short to power | Yes | $20–100 |
| Replace the pressure differential switch | Yes | $50–150 |
| Clean or replace the ABS connector and terminals | Yes | $10–40 |
| Replace the ABS control module | Mechanic | $300–800 |
Frequently asked questions
Can I drive with C1240?
Yes, in most cases the regular brakes still work, but the ABS is disabled. Have the wiring checked soon because a short to power can damage other parts.
What does a short to battery mean?
It means part of the circuit has power flowing where it should not. A damaged wire touching a power wire is the usual cause.
Will replacing the ABS module fix C1240?
Only if the module is the problem. A shorted wire or a bad pressure switch is more common, so check those first.
Related codes
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.