What does it mean?
OBD II fault code C1446 is a manufacturer specific code that is defined by carmakers Ford, Lincoln, Mercury, Mazda, and Jaguar as “Brake Switch Circuit Failure (ABS Module) Open or Shorted to Ground”, and is set when the PCM (Powertrain Control Module) on these applications detects an open, or, short circuit in the control circuit of the brake switch. The brake switch is sometimes also known as the “brake light switch”, “brake pressure switch”, or “cruise control deactivation switch”.
NOTE: Code C1446 typically sets when the PCM detects an “ON” signal from the brake switch for about six consecutive minutes while the vehicle is being driven faster than 12 m/ph, or, when a continuous “ON” signal from the brake switch is detected even when one or more control modules detect that the vehicle is actually slowing down. On modern applications that are fitted with ABS brakes, stability -, traction control, and other safety systems, the brake switch performs two functions.
The first is that activating the switch by depressing the brake pedal illuminates the brake lights; the second is that by activating the switch, the PCM, and other control modules are alerted that the brakes are being applied. While the need for the first function is self-explanatory, the second function is essential for safe vehicle operation.
For instance, if the cruise control system is in operation, it cannot be deactivated by momentarily depressing the brake pedal if the brake switch or its control/signal circuit is defective, since both the PCM and ABS control modules depend on the brake switch to receive accurate input data in order to be able to deactivate the cruise control system.
Thus, if the relevant control modules do not receive an input signal from the brake switch, or if one or more control modules receive an input signal, even though the wheel speed and/or other sensors detect that the vehicle is decelerating, the cruise control system will remain active, unless it is deactivated manually.
Moreover, if the brake switch or its control circuit is defective, it may be impossible to move the gear selector out of “P”, on many, if not most applications, since the gear selector lockout switch requires a signal from the brake switch to release. In terms of operation, the brake switch is a simple “ON-OFF” switch that is most commonly located on the brake pedal, and always supplied with current on one terminal.
Depressing the brake pedal allows moving parts in the switch to close a circuit, which then supplies current through the switch to the brake light circuit(s), various control modules, as well as to the gear selector safety lockout switch via separate terminals on the “current out” side of the switch.
Thus, should the PCM or other control module detect an open circuit, short circuit to (battery negative), or a general malfunction in the switch and/or its associated circuit(s), code C1446 will be set, and an ABS warning light may be illuminated as well.
Symptoms
- ABS or stability warning lamp on, sometimes together with the MIL (check engine lamp)
- Brake lights inoperative, permanently on, or working intermittently
- Cruise control will not engage, or will not cancel when the pedal is pressed
- Selector cannot be moved out of Park on vehicles with a shift interlock
- Auto hold, hill hold and stop-start disabled
- Code sets after a long steady drive when the signal stays active
Likely causes
- Failed or badly adjusted brake light switch, including contacts that stay closed
- Broken or missing pedal striker pad, leaving the plunger permanently released
- Open circuit or a chafed wire between the switch and the control module
- Short to ground on the brake switch signal wire
- Corroded, loose or overheated switch connector terminals
- Blown stop lamp fuse or an open supply to the switch
- Aftermarket alarm, remote start or trailer wiring spliced into the brake circuit
How to fix it
- Check the stop lamp fuse and observe the brake lights while an assistant presses the pedal
- Watch the brake switch parameter on a scan tool and confirm it changes cleanly from off to on
- Inspect the switch adjustment and the pedal striker pad; a broken pad is a frequent cause
- Backprobe the switch for supply voltage and a switched output at both output terminals
- With the switch unplugged, test the signal wire for continuity to the module and for a short to ground
- Look for aftermarket splices, trailer wiring or repairs in the brake light circuit
- Adjust or replace the switch, clear the code and confirm the parameter behaves correctly during a road test