C1421 – Damper LF Circuit Short to Battery (Ford) / Open or Short in Master Cylinder Pressure Sensor (Toyota)

By Benjamin Jerew (Contact Me)
Last Updated 2016-11-30
ASE Master Tech

Trouble CodeFault LocationProbable Cause
C1421 Damper LF Circuit Short To Battery (Ford, Jaguar) Open or Short in Master Cylinder Pressure Sensor (Toyota) Rear Differential Clutch Performance (Jeep, Chrysler)

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What Does Code C1421 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.

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.

What are the symptoms of code C1421?

Depending on the vehicle, a fault related to DTC C1421 may exhibit itself in different ways.

  • Toyota vehicles braking may be inhibited and safety systems like ABS, brake assist, and traction control may be disabled.
  • Ford vehicles may default to the firmest suspension setting, resulting in a firmer-than-normal ride quality.
  • Jeep vehicles, in slippery situations, will not deliver the expected traction boost on demand.

How do you troubleshoot code C1421?

Troubleshooting these systems depends entirely on which vehicle you are working on.

  • Toyota says to simply replace the brake actuator. Check with a professional before condemning this multi-thousand-dollar component.
  • Ford adaptive suspension systems will require an EWD and DMM (electrical wiring diagram and digital multimeter) to find the short circuit. Do not forget to check the circuit and the solenoid itself.
  • If a Differential Lock is commanded, but the control unit sees excessive wheel slip, it will determine that there's a problem in the system.
    If a Differential Lock is commanded, but the control unit sees excessive wheel slip, it will determine that there’s a problem in the system.

    Jeep vehicles may require both electrical and hydraulic tests to determine why it is slipping while lockup is commanded.

Codes Related to C1421

Toyota includes a couple more DTCs referring to problems with the master cylinder pressure sensor:

Ford, Jaguar, Others have similar DTCs referring to circuit problems at all four dampers:

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