C1239: ABS Hydraulic Pressure Differential Switch Input Open Circuit
What does C1239 mean?
C1239 is a diagnostic trouble code indicating "ABS Hydraulic Pressure Differential Switch Input Open Circuit". This means there is an electrical break in the anti-lock brakes wiring — a connector may be unplugged, a wire broken, or a component has failed internally. The ECU detected no signal where it expected one.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- ABS warning light on
- Brake pedal feels different
- Unusual braking behaviour
- Intermittent warning lights
Estimated repair cost
Typical range in Australia (parts + labour)
Common causes
- Damaged or corroded wiring harness
- Loose or disconnected electrical connector
- Failed anti-lock brakes sensor or actuator
- Blown fuse in the related circuit
- Poor ground connection
What should you do?
This code sits in the braking system. Your normal hydraulic brakes generally still work, but the electronics layered on top of them, ABS, EBD and emergency brake assist, can drop out. You will not notice until you brake hard or brake on a wet or loose surface, and that is the moment they would have helped. Treat the car as needing a workshop rather than as safe to drive, and get it looked at before your next real trip.
Get a diagnosis for YOUR car
Code C1239 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.