Fix P0556: Mechanic’s solutions that WORKED

The P0556: Brake Booster Pressure Sensor Circuit Range/Performance code indicates a problem with the brake booster pressure sensor circuit. This sensor is a key part of the vehicle’s braking system, as it helps to ensure that the brakes are functioning correctly and efficiently. When the sensor or its circuitry malfunctions, it can lead to braking issues, which is why addressing this code is important for maintaining safe driving conditions.

P0556 quick overview

Description	P0556: Brake Booster Pressure Sensor Circuit Range/Performance
Is it serious?	This code is moderately serious as it relates to the vehicle’s braking system, which is crucial for safe driving.
Possible causes	– Faulty brake booster pressure sensor – Vacuum leaks in the brake booster system – Electrical issues in the sensor circuit – Brake fluid level or quality issues
How to diagnose?	Inspect Brake Booster System: Examine the brake booster and its components for any signs of damage or malfunction. Check for Vacuum Leaks: Look for leaks in the vacuum lines connected to the brake booster. Test Brake Booster Pressure Sensor: Evaluate the functionality and electrical connections of the brake booster pressure sensor. Assess Brake Fluid: Verify the brake fluid level and quality, ensuring it meets the required standards. Clear and Re-monitor Codes: After addressing potential issues, clear the fault codes and monitor the vehicle to see if the code reappears.

How to fix P0556 – learn from mechanics

I looked into P0556 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Porsche

Vehicle Information: 2014 Porsche Cayenne S Hybrid 3.0L

Issue + Repair History:

• Check engine light led to discovery of codes P0556 & P1479.
• Initial repair involved replacing a burnt-out electric vacuum pump and melted vacuum hose.
• SUV returned two days later with the same codes; vacuum pump burnt out again and hose melted.
• Technician inspected relay but couldn’t confirm if it was sticking.

Other OBD2 Codes + Test Results:

• P0556: Brake booster pressure sensor circuit performance
• P1479: Brake booster vacuum system mechanical failure open circuit

Suggestions to Fix Issue:

• Check for a leaky brake booster causing the vacuum pump to stay running.
• Investigate if a bad pressure sensor is causing a false low reading, making the pump run constantly.
• Review the vacuum switch and pump circuit for constant power.
• Apply an external vacuum source to the vacuum circuit to locate the leak.
• Consider the possibility of a faulty vacuum sensor, check valve, or other leaks in the system.

Final Fix:

• Replaced the sticking relay, along with a new pump and vacuum hose.
• Monitored vacuum using a mechanical pump and scanner, checking for leaks overnight.
• The replaced relay was from a different manufacturer and color.

Case #2: Saturn

Vehicle Information: 2007 Saturn Vue Green Line 2.4L

Issue + Repair History:

• Vehicle repeatedly showing about 21 codes, mostly communication-related.
• Notable codes include P1A6F (“Starter generator no crank at restart”) and P0556 (“Brake booster performance”).
• Inconsistent occurrence of communication issues during road tests, with modules sporadically dropping out.
• Similar symptoms observed in another vehicle of the same model at a different store.
• Visual inspections and wire wiggling have not identified any problems.
• Found TSB regarding transmission cooler line restriction affecting torque converter clutch and start-stop system.
• Difficulty replicating issues to pinpoint a specific cause.

Other OBD2 Codes + Test Results:

• P1A6F: Starter generator no crank at restart
• U1886: BEM lost comm with PCM
• U0111: Lost comm with BEM
• U0073: No comm with CAN network
• P0700: Trans module request MIL
• P0556: Brake Booster performance

Suggestions to Fix Issue:

• Check the CAN bus with a scope for voltage, resistance, and signal clarity.
• Inspect all vehicle grounds and check battery voltage and alternator output.
• Investigate the engine harness near the left side of the head purge solenoid bracket for chafing.
• Perform voltage drop tests on main grounds and power while cranking.
• Consider past vehicle repairs or replacements that might have caused wiring or module issues.

Final Fix:

• Replaced transmission lines as per TSB regarding the torque converter issue.
• Could not definitively resolve all issues due to the intermittent nature of the problem.
• Noted that further problems might exist, but the vehicle seemed okay after road testing post-repair.

Case #3: Acura

Vehicle Information: 2008 Acura RDX 2.3L

Issue + Repair History:

• Experienced pinging and misfire during a drive, particularly under load with the turbo engaged.
• Idle was normal when stopped.
• Scanned for codes, found two related to brake pressure sensor and one pending misfire code.
• No significant changes in fuel trim data from when the issue occurred.
• Previously replaced serpentine belt, spark plugs, and valve adjustment suggested but not completed.

Other OBD2 Codes + Test Results:

• PO556: Brake booster pressure sensor range/problem
• P15BA: Check valve stuck closed
• PO302: (Pending) Misfire on cylinder #2

Suggestions to Fix Issue:

• Check for vacuum pump issues and replace the check valve and hose kit.
• Use a vacuum gauge to check for a restricted exhaust.
• Perform a diagnostic test on the brake booster pressure sensor.
• Check fuel pressure and vacuum readings.
• Scope the ignition coils for irregular patterns.
• Consider swapping coils and plugs to different cylinders to isolate the issue.

Final Fix:

• Replaced the check valve in the vacuum hose to the booster, improving but not fully resolving the issue.
• Performed a reflash for the code P15BA, which eliminated the misfire and pinging.
• Reinstalled old spark plugs after confirming new ones did not fix the problem.
• Addressed the brake booster pressure sensor issue.

Case #4: Chevrolet

Vehicle Information: 2012 Chevrolet Cruze 1.8L

Issue + Repair History:

• Check engine light activated with a P0556 code for brake booster pressure sensor circuit.
• Reported intermittent issues with braking efficiency.
• Previous repairs included brake pad replacement and brake fluid change.

Other OBD2 Codes + Test Results:

• P0556: Brake Booster Pressure Sensor Circuit Range/Performance

Suggestions to Fix Issue:

• Conduct a full inspection of the brake booster and its pressure sensor.
• Test the brake booster pressure sensor circuit for any electrical faults.
• Examine all related vacuum lines for leaks or damage.
• Check the brake fluid level and quality.
• Consider replacing the brake booster pressure sensor if it shows signs of failure.

Final Fix:

• Found and repaired a small vacuum leak in a line connected to the brake booster.
• Replaced the brake booster pressure sensor due to failure in circuit performance tests.

Case #5: Ford

Vehicle Information: 2010 Ford F-150 XLT 5.4L

Issue + Repair History:

• Engine light came on, and diagnostics revealed a P0556 code.
• Driver experienced occasional hard braking.
• Recent services include regular maintenance and tire rotation.

Other OBD2 Codes + Test Results:

• P0556: Brake Booster Pressure Sensor Circuit Range/Performance

Suggestions to Fix Issue:

• Inspect the brake system, focusing on the brake booster and its components.
• Perform an electrical check of the brake booster pressure sensor circuit.
• Ensure there are no vacuum leaks in the system affecting the brake booster.
• Test the brake booster pressure sensor for proper functionality.
• Reset the code and monitor if it reappears after repairs.

Final Fix:

• Replaced a faulty brake booster pressure sensor.
• Conducted a brake system bleed to ensure proper fluid distribution.
• Cleared the code, and upon further testing, the issue did not reappear.

Common Advice for P0556	Brief Description of Diagnostic Step
Inspect Brake Booster and Pressure Sensor	Check the brake booster and its pressure sensor for signs of malfunction.
Check for Vacuum Leaks	Examine vacuum lines connected to the brake booster for leaks or damage.
Test Sensor Circuit	Perform electrical tests on the brake booster pressure sensor circuit.
Evaluate Brake Fluid Quality and Level	Ensure the brake fluid is at the correct level and free from contamination.
Replace Faulty Components	Replace any malfunctioning parts such as the brake booster pressure sensor.
Reset and Re-monitor Codes	After repairs, clear the codes and monitor to see if the issue reoccurs.