What does it mean?
If you have a check engine light (CEL) with DTC C1421 set in system memory, this may refer to different systems, depending on which vehicle you are working on. That’s because C1XXX DTCs (diagnostic trouble codes) are manufacturer-dependent. In other words, Toyota’s definition may be different from Ford’s definition, and so on. The Brake Warning Light will most likely illuminate if you have a Toyota Brake Actuator problem.
Toyota vehicles equipped with an electro-hydraulic brake booster use a number of sensors and actuators to assist the driver. The system usually includes hydraulic brake boosting, anti-lock braking (ABS), brake assist (panic braking pressure boost), and traction control. The Skid Control ECU (electronic control unit) is integrated into the Brake Actuator Assembly, and uses the master cylinder pressure sensor to monitor brake fluid pressure.
If the Skid Control ECU detects a problem with the pressure sensor, it will go into a backup mode and set a DTC and warning light. DTC C1421 is defined as “Open or Short in Master Cylinder Pressure Sensor.” Ford, Jaguar, and other vehicles use this code in reference to the adaptive suspension system. In adaptive suspension systems, the chassis control ECU uses solenoid valves to control hydraulic fluid flow in the shock absorbers or dampers.
More fluid flow gives a softer ride, while less fluid flow gives a firmer ride. If the chassis control ECU detects a problem in the circuit to one of the damper solenoids, it will go into a default mode, if possible, and set a warning light. DTC C1421 is defined as “Damper LF (Left Front) Circuit Short to B+ (Battery). Jeep, Chrysler, and other vehicles use this code in reference to the rear differential lock.
In vehicles equipped with electronically controlled AWD or 4WD (all-wheel drive or four-wheel drive) systems, the system uses valves to lock and unlock front, center, and rear differentials as needed. Locked differentials can improve traction in many situations. If the ECU detects excessive wheel spin when it is commanding lockup, it interprets this as a failure in the rear differential clutch.
DTC C1421 is defined as “Rear Differential Clutch Performance.” There may be other definitions related to DTC C1421, but these appear to be the most common.
Symptoms
- Brake warning, ABS or suspension warning lamp depending on the system involved
- Firmer or longer brake pedal and reduced boost where the pressure sensor is at fault
- Harsh, uncontrolled or uneven ride quality where a damper circuit is at fault
- All wheel drive or differential lock indicator lit with poor traction and wheel spin
- Stability and traction control disabled
- Fault may appear only when cold, over bumps or during hard cornering
Likely causes
- Open or shorted wiring to the brake master cylinder pressure sensor on vehicles with an electro-hydraulic brake booster
- Failed pressure sensor element, or moisture in its connector at the brake actuator assembly
- Left front damper solenoid control wire rubbed through and touching a battery feed on adaptive suspension systems
- Internally shorted damper solenoid winding, or water in the strut top connector
- Worn rear differential clutch pack, or wrong and degraded differential fluid on electronically locking axles
- Excessive wheel spin detected while lockup was commanded, often caused by mismatched tyre sizes
- Failed control module output driver or a corroded module connector
How to fix it
- Note which warning lamps are on and which module stored the code; that identifies the system
- Read live data for the suspect circuit: brake pressure value at rest, damper solenoid current, or clutch duty and wheel speeds
- Inspect the relevant connector for water and corrosion, especially at the brake actuator or the strut tower
- Measure the sensor or solenoid resistance and compare it with specification
- With the component unplugged, check the control wire for a short to battery voltage or to ground
- Check tyre sizes, pressures and differential fluid condition where the differential clutch definition applies
- Repair the wiring or replace the failed sensor, solenoid or clutch assembly, then clear the code and road test