Open or Short in Master Cylinder Pressure Sensor

What C1421 means

The master cylinder pressure sensor tells the skid-control ECU how hard you are pressing the brakes so it can manage stability control (VSC), traction control and brake assist. C1421 sets when the sensor's supply voltage or its pressure signal stays outside the expected window for more than about a second - for example the ~5-volt supply drifting out of range, or the pressure signal reading implausibly low or noisy. Because the sensor is integrated into the brake actuator on these Toyotas, it cannot be replaced on its own, which is why the factory fix is to replace the brake actuator assembly and then recalibrate the system. It is often stored alongside C1422, C1423 or C1424, which describe related zero-point and output faults of the same sensor.

Symptoms

• ABS warning light on
• VSC/traction (skid) and slip indicator lights on
• Brake system warning light on
• Stability control, traction control and brake assist disabled (normal braking still works)
• Often stored together with C1422, C1423 or C1424

Common causes

• Internal fault in the master cylinder pressure sensor, which is part of the brake actuator (ABS/VSC) assembly
• Open, short or corrosion in the sensor's supply or signal wiring or its connector
• Poor ground or low system voltage while driving
• Damaged or backed-out pins at the brake actuator connector
• Failed brake actuator assembly; rarely, a faulty skid-control ECU

Severity & driving advice

Severity: Moderate — Stability and traction control are disabled; base brakes still work, so drive gently.

Can I drive? You can drive, but with ABS, traction and stability control off the car won't help you in a slip or panic stop - fix it promptly, especially before wet or icy weather.

Diagnostic approach

1. Read all chassis codes — Scan the ABS/VSC system and note any companion codes (C1422-C1424) that point at the same sensor.
2. Check charging and grounds — Confirm healthy battery and charging voltage - low or unstable voltage can trip this code without a sensor fault.
3. Inspect the actuator connector and wiring — Look for corrosion, backed-out terminals or chafed wiring at the brake actuator; repair before condemning the sensor.
4. Check sensor supply and signal — With the actuator connected, verify the sensor's supply and pressure-signal voltages against specification.
5. Replace the brake actuator assembly if internal — If wiring and voltages are good but the signal is still out of range, the integral pressure sensor is faulty; the sensor is not sold separately, so the brake actuator assembly is replaced.
6. Calibrate and reset — After repair, perform the yaw-rate/acceleration sensor zero-point calibration and the test-mode signal check, then run the ABS-light reset drive cycle and clear the codes.

Estimated repair costs

Typical US repair costs (parts & labour) for the faults behind C1421. These are national-average estimates, not a quote— your actual price varies by region, shop labour rate, and your vehicle’s make, model and year. Figures reviewed 2026.

Make & model notes

Toyota: Applies across 2014 Toyota models that use the brake-actuator-integrated pressure sensor - including Corolla, RAV4, 4Runner, Tacoma, Highlander and FJ Cruiser. Because the pressure sensor is part of the brake actuator (ABS/VSC) assembly, C1421 is diagnosed at the actuator, not as a separate sensor.

FAQ