What does it mean?
P1805 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Brake Switch Signal Malfunction (Includes Hybrid Models) .
Symptoms
- MIL (check engine lamp) is on and the brake lights stay on or do not work at all
- The selector will not come out of park because the shift interlock does not release
- Cruise control cannot be set or cancels itself
- Auto start-stop stops working
- On hybrids, regenerative braking is reduced and the brake pedal feel changes
- Harsh feel when slowing, as the converter clutch does not release on time
Likely causes
- Brake light switch out of adjustment or with worn internal contacts
- Crushed or missing rubber pedal stop pad, changing where the switch plunger sits
- Corroded or loose connector at the pedal bracket, a damp area under the dash
- Open, shorted or high-resistance wire in the brake switch circuit
- Blown brake lamp fuse, which also removes the switch supply on many vehicles
- Aftermarket accessory such as an alarm, trailer module or camera spliced into the brake circuit
- On hybrids, disagreement between the brake switch and the brake pressure or pedal travel signal
How to fix it
- Check brake lamp operation, including with only light pedal pressure
- Watch all brake-related signals in live data while pressing the pedal very slowly and note whether they change together
- Check the brake lamp fuse and the switch supply with the ignition on
- Inspect and renew the pedal stop pad, then adjust the switch to specification
- Inspect the connector and wiring at the pedal for corrosion and damage, and disconnect any aftermarket device on the circuit
- Replace the brake switch, readjust it and confirm every brake signal now tracks the pedal correctly