C0021: Brake booster performance or signal fault (Dodge and Jeep)

Brake booster performance / general signal failure

Severity: Inspect soon

Owners on Dodge and Jeep vehicles report a stiff pedal or lost brake assist with this code, so the braking effort changes.

It gets more serious if:

Stop: Stop and have it towed if the brake pedal goes hard or sinks, or the brake warning light and a brake system failure message show.

Safety-critical system: explanation only, no DIY steps. Source: how we rate severity

C0021 in short

On Dodge and Jeep, C0021 means the brake booster is not performing or its signal has failed. Owners report a hard pedal or lost assist, sometimes tied to a brake booster recall. Treat it as a brake fault and have the vehicle inspected promptly.

On the Dodge and Jeep vehicles we could source, C0021 is about the electronic brake booster, not a wheel speed sensor as some code lists say. A Dodge Grand Caravan owner reports Dodge service showing C0021 brake booster performance, and a Durango owner reports C0021-02 brake booster general failure. Jeep owners quote dealers giving brake booster general signal failure on a Grand Cherokee and electronic brake booster failure on a Grand Wagoneer.

Owners describe a stiff pedal, hissing noises or a brake system failure message. The Durango owner ties the message to water in the booster freezing and to a brake booster recall.

We have not verified other makes; Chevrolet and Ram owners also report C0021 but we could not source what it means there.

Pick your make

C0021 is a manufacturer-specific code: its meaning depends on who built the car.

Other makes: meaning not verified. Check with a scan tool that reads manufacturer definitions.

Most likely causes

Cause 1: Electronic brake booster or its signal
Supported by vehicle data
Why it ranks here
Dealer and owner readouts on Dodge and Jeep name the brake booster for C0021.
What would change this
Rises if the pedal feels stiff or the booster hisses. Falls if the pedal feels normal and the code is history only.
Cause 2: Brake control module
Possible — needs testing
Why it ranks here
The Grand Wagoneer dealer listed the brake control module along with the booster.
What would change this
Rises if the booster tests good and the code returns. Falls if the booster is faulty.
How to test the brake system control module (abs module)

What to test first

Start at step 1. Each result tells you what it means and where to go next.

Step 1: Note whether the brake pedal feels hard, high or sinks, and whether the red brake light or a brake system message shows. If it does, stop driving.
Low risk
Warning:Do not keep driving with a hard or sinking pedal.
- IfThe pedal is hard, high or sinking, or a brake failure message shows
  It meansBrake booster failure; have it towed.
  Points to: Electronic brake booster or its signal
- IfThe pedal feels normal and the code is stored only
  It meansHave a shop read the booster data and check recalls for your VIN.
  Go to step 2
Step 2: Have a shop check recalls for your VIN and run the booster and brake module self-tests.
Best left to a shopTool: scan tool
Warning:This is a brake system. Leave testing and repair to a shop.
- IfThe booster fails its test
  It meansBooster fault.
  Points to: Electronic brake booster or its signal
- IfThe booster passes and the code returns
  It meansBrake module suspect.
  Points to: Brake control module

Symptoms

Brake pedal hard or high, needs much more effort Gets more serious: stop and have it checked.
Hissing noise from the pedal area when braking
ABS, brake or traction control lights and a brake system message
Brake or ABS warning light on together with the stability control light Gets more serious: stop and have it checked.

How to fix

This is a safety-critical system, so we explain the code but don't give repair steps. Have it inspected by a qualified technician.

On your vehicle

Jeep

2012 · Grand Cherokee
Supported by vehicle data
An owner reports the dealer reading C0021-02 as brake booster general signal failure after a brake booster recall.

Dodge

2014 · Durango
Supported by vehicle data
An owner reports C0021-02 brake booster general failure in freezing weather and links it to a booster recall.

No curated relationships for C0021 yet.

All ABS, traction and stability control codes

C0021 questions

Is C0021 a wheel speed sensor code?

On the Dodge and Jeep vehicles we could source, no. Owners quote it as a brake booster fault.

Sources and review

NHTSA complaint ODI 11716853: 2014 Dodge Durango brake booster message — NHTSA Office of Defects Investigation
NHTSA complaint ODI 11689771: 2023 Jeep Grand Wagoneer no brakes — NHTSA Office of Defects Investigation
NHTSA complaint ODI 10781320: 2010 Dodge Grand Caravan acceleration and brakes — NHTSA Office of Defects Investigation
NHTSA complaint ODI 11491725: 2012 Jeep Grand Cherokee brake booster — NHTSA Office of Defects Investigation

Last reviewed: October 15, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

Severity: Inspect soon

Pick your make

Most likely causes

Cause 1: Electronic brake booster or its signal

Cause 2: Brake control module

What to test first

Step 1: Note whether the brake pedal feels hard, high or sinks, and whether the red brake light or a brake system message shows. If it does, stop driving.

Step 2: Have a shop check recalls for your VIN and run the booster and brake module self-tests.