What does code C1391 mean?

The code C1391 is a chassis diagnostic trouble code used by many vehicles. There is no universal meaning for C1391; the exact fault it represents depends on the manufacturer and model. Broadly, it points to a chassis/ABS/traction-control domain and related wiring or modules.

Understanding the code and who uses it

In OBD-II terminology, C codes cover chassis systems. C1391 appears in diverse makes and generations, and each automaker can map the code to a different component or fault within the chassis network. As a result, the same alphanumeric code can have distinct meanings from one vehicle to another. Knowing the precise definition requires the vehicle’s specific repair manual or an OEM diagnostic tool.

Manufacturer-specific definitions

Some manufacturers associate C1391 with ABS/ESC (electronic stability control) network issues, while others tie it to wheel-speed sensor circuits, communication between control modules, or related wiring. Because the exact decoding varies by brand and year, always consult the manufacturer's DTC tables for your vehicle.

Common causes

Before diagnosing, it helps to know the range of issues most often linked to C1391 across different models. The following list covers typical possibilities encountered by technicians.

• Faulty ABS/ESC control module or software issue


• Wheel speed sensor (WSS) circuit problems or damaged wiring


• Brake actuator or hydraulic control unit fault


• Damaged wiring harness or poor grounding to chassis modules


• CAN bus or other network communication errors between ABS/ESC and other controllers


• Blown fuse or power supply issue to chassis control modules

Concluding note: Because C1391 definitions vary by maker, verify the exact meaning with your vehicle’s OEM service information before pursuing any repair.

Diagnosis and next steps

To identify the precise cause of C1391 and determine the correct repair, follow a structured diagnostic workflow using OEM tooling when possible.

1. Record the full DTC readout, including the exact manufacturer code, freeze-frame data, and conditions when the fault appeared.


2. Check for any related chassis or ABS/ESC codes and address obvious issues first (e.g., low battery, damaged grounds).


3. Inspect ABS/ESC components and wiring: fuses, power and ground connections, and module harnesses for corrosion or damage.


4. Test wheel speed sensor circuits: inspect connectors, wiring runs, and sensor integrity; measure sensor resistance if the vehicle supports it.


5. Examine CAN bus and module communications: look for damaged cables, improper routing, or moisture near connector points.


6. Verify vehicle power and grounding: ensure stable 12V supply, proper charging, and clean, tight grounds.


7. Run OEM ABS/ESC self-tests and calibrations with the diagnostic tool; observe sensor readings and module status during operation.


8. Plan the repair based on findings: replace faulty sensors or modules, repair wiring, or perform software updates and recalibration as specified by the manufacturer.

Concluding note: Some repairs require dealer-level programming or calibration. If the diagnostic data point to a module or sensor replacement, a professional technician with proper tooling is often the safest course.

Summary

Code C1391 signals a chassis-related fault, most commonly tied to ABS/traction control systems, but its exact meaning is not universal. The precise decoding depends on the vehicle maker, model year, and the diagnostic tool used. Start with OEM documentation and a careful diagnostic workflow to identify whether the issue lies with sensors, wiring, or control modules, and proceed with the appropriate repair or calibration.

How do I know if my Prius brake actuator is bad?

Common symptoms of a failing Prius brake actuator include dashboard warning lights (ABS, Brake, or VSC), strange noises like buzzing or grinding, and a soft or sinking brake pedal. You may also notice issues with braking performance, such as reduced braking power, uneven braking, or the need for increased effort to stop.
 
Dashboard indicators 

• Warning lights: The brake, ABS, or VSC lights may illuminate on the dashboard. 
• Persistent buzzing: A persistent or intermittent buzzing sound can be a sign of strain on the brake system. 

Pedal and braking feel 

• Spongy or soft pedal: The brake pedal feels unusually soft or sinks to the floor when pressed. 
• Increased pedal effort: You may need to press the brake pedal harder to stop the car. 
• Uneven braking: The vehicle may pull to one side when braking. 
• Brake failure: In severe cases, the brakes may fail completely, and the car may coast to a stop despite the pedal being pressed. 

Other sounds and issues

• Unusual noises: You might hear grinding, squealing, or clicking sounds when you apply the brakes. 
• Actuator running constantly: A failing actuator's pump may run frequently, even when the brake pedal is not being pressed, due to internal leaks. 
• Brake fluid leaks: Look for any signs of fluid leaking around the actuator or master cylinder. 

What is the recall on the Toyota C1391?

Toyota is providing coverage for repairs related to the certain internal malfunctions of the brake booster assemblies. One or more of the following specific Diagnostic Trouble Codes (DTCs) C1391, C1252, C1256 or C1253 will be stored in the vehicles memory to be used as verification.

How do you fix the code C1391?

Fixing the C1391 Error Code
To resolve this issue, we replace the faulty brake master cylinder and brake booster accumulator with original Toyota parts. After installation, we perform a full system calibration to ensure proper brake operation and restore the vehicle's safety features.

What is the abnormal leak of ACC press C1391?

The C1391 code indicates an abnormal leak in the brake accumulator pressure, meaning the ABS system cannot build sufficient pressure for proper power braking. This is often caused by worn seals or hoses within the brake actuator assembly, a failing brake booster, or other internal leaks. This can lead to a loss of power brakes and potentially trigger warning lights, and it's recommended to stop driving and have the system inspected, as a component replacement is often required.
 
Causes of the C1391 code

• Internal leaks in the brake actuator: Degraded internal seals in the brake booster/accumulator assembly are a common cause. 
• Leaking brake lines or hoses: Cracks or wear in the rubber hoses or brake lines can cause pressure loss. 
• Faulty components: The code can also be triggered by a failing vacuum pump, malfunctioning check valves, or other issues within the brake system. 

What to do

• Stop driving immediately: Do not continue to drive the vehicle, as it is unsafe with a failing brake system. 
• Check for recalls: Before making repairs, check with Toyota to see if there are any recalls or extended warranty coverage for your vehicle's brake system. 
• Inspect the system: A professional should inspect the entire brake actuator assembly, including the master cylinder, accumulator, and lines, for any signs of leaks or damage. 
• Be prepared for replacement: Repairs typically involve replacing the entire brake actuator assembly, which can be a complex and expensive job. 
• Use a professional scan tool: A professional may need to use a specific diagnostic tool, like a Toyota Techstream, to clear the codes after the repair is completed.