Pre-Collision Brake Actuator Circuit
2017-2017 Mazda MX-5 Miata 2.0L I4
The 2017 Mazda MX-5 Miata is equipped with a 2.0L inline-4 engine. Below you'll find detailed c0421 diagnostic code information including labor time estimates, cost ranges, and technician notes specific to this engine configuration.
Description
Malfunction in the brake actuator used by the pre-collision system to automatically apply brakes.
Symptoms
- PCS warning light
- Automatic braking will not activate
- Pre-collision system disabled
Common Causes
- Brake actuator solenoid failure
- ABS modulator fault affecting PCS
- Wiring to actuator damaged
- Actuator mechanically stuck
Diagnostic Steps
- Test brake actuator solenoid resistance
- Command actuator with scan tool
- Check for ABS codes that disable PCS
- Inspect actuator wiring
- Test brake pressure response to PCS command
Repair Notes
Replace brake actuator or repair ABS modulator. PCS brake actuation may use the ABS hydraulic unit.
Related Codes
Other Chassis Codes
- C0021LF Wheel Speed Sensor Range/Performance
- C0022RF Wheel Speed Sensor Range/Performance
- C0023LR Wheel Speed Sensor Range/Performance
- C0024RR Wheel Speed Sensor Range/Performance
- C0025LF Wheel Speed Sensor Circuit Intermittent
- C0026RF Wheel Speed Sensor Circuit Intermittent
- C0027LR Wheel Speed Sensor Circuit Intermittent
- C0028RR Wheel Speed Sensor Circuit Intermittent
- C0035Left Front Wheel Speed Sensor Circuit
- C0036Left Front Wheel Speed Signal Erratic
C0421 on Other Vehicles
Common Questions
What does code C0421 mean on a 2017-2017 Mazda MX-5 Miata?
C0421 stands for "Pre-Collision Brake Actuator Circuit". Malfunction in the brake actuator used by the pre-collision system to automatically apply brakes.
What are the symptoms of C0421 on a Mazda MX-5 Miata?
Common symptoms of C0421 include: PCS warning light, Automatic braking will not activate, Pre-collision system disabled.
What causes C0421 on a 2017-2017 Mazda MX-5 Miata?
Common causes of C0421 include: Brake actuator solenoid failure, ABS modulator fault affecting PCS, Wiring to actuator damaged, Actuator mechanically stuck.
Last updated: March 2026