C0021 Trouble Codes and Diagnostics

The OBD-II code C0021 indicates a problem with the performance of the brake booster. The brake booster, also known as the power brake booster, is a component that assists in applying the necessary force to the brake pedal to stop the vehicle efficiently. It typically uses vacuum from the engine or a separate vacuum pump to provide the additional force.

Symptoms:

Hard Brake Pedal, Increased Stopping Distance, Spongy or Soft Brake Pedal, Brake Pedal Sinks to the Floor or Check Engine Light

Possible Causes of C0021 Code :

• Vacuum Leak: A leak in the vacuum system can reduce the effectiveness of the brake booster. Common sources of leaks include hoses, the vacuum check valve, or the booster diaphragm itself.
• Faulty Vacuum Check Valve: The vacuum check valve ensures that the vacuum is maintained in the brake booster when the engine is off. A faulty valve can allow air to enter the system, reducing the booster's performance.
• Worn or Damaged Brake Booster Diaphragm: The diaphragm inside the brake booster can wear out over time or become damaged, leading to a loss of vacuum and reduced braking assistance.
• Low Engine Vacuum: If the engine is not producing sufficient vacuum, the brake booster may not function correctly. This can be due to issues like a clogged air filter, a malfunctioning EGR valve, or other engine problems.
• Electrical Issues: In some vehicles, the brake booster performance is monitored by the ECU. Faulty sensors or wiring can trigger this code.

How to Fix It?

Be sure to check for any damaged components and inspect the connector pins for signs of being broken, bent, pushed out, or corroded.

Common Diagnoses and Repairs:

• Inspect Vacuum Hoses: Check all vacuum hoses connected to the brake booster for leaks, cracks, or disconnections. Replace any damaged hoses.
• Test Vacuum Check Valve: Remove the vacuum check valve and test it for proper function. If it allows air to pass in both directions, it needs to be replaced.
• Inspect Brake Booster Diaphragm: If the diaphragm is damaged or worn, it will need to be replaced. This often requires replacing the entire brake booster unit.
• Check Engine Vacuum: Use a vacuum gauge to measure the engine vacuum. If the vacuum is low, diagnose and repair the underlying engine issue.
• Check Electrical Connections: Inspect the electrical connections and sensors related to the brake system for any signs of damage or corrosion.
• Consult a Professional: If you are not comfortable with these tasks, consult a professional mechanic for a thorough diagnosis and repair.