C05B9 — Brake Booster Motor A Position Sensor Supply Circuit Low

What Does C05B9 Mean?

C05B9 is a diagnostic trouble code indicating: Brake Booster Motor A Position Sensor Supply Circuit Low. This code relates to the chassis system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of C05B9

⚠️ Check Engine Light (MIL) illuminated
⚠️ Brake Booster Motor A Position Sensor Supply reading at zero or minimum value
⚠️ Related system not functioning or in fail-safe mode
⚠️ ABS or stability control warning light

Common Causes

🔍 Open or broken wire in Brake Booster Motor A Position Sensor Supply circuit
🔍 Poor ground connection at Brake Booster Motor A Position Sensor Supply
🔍 Faulty Brake Booster Motor A Position Sensor Supply with no output signal
🔍 Disconnected or loose Brake Booster Motor A Position Sensor Supply connector
🔍 Blown fuse in related circuit

Frequently Asked Questions

What does C05B9 mean?

C05B9 indicates: Brake Booster Motor A Position Sensor Supply Circuit Low. The vehicle's computer has detected that the Brake Booster Motor A Position Sensor Supply is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code C05B9?

Only short distances if absolutely necessary. C05B9 affects a critical system and should be diagnosed within a few days to avoid further damage.

How much does it cost to fix C05B9?

Repair costs for C05B9 typically range from $20 to $400, depending on the root cause. Simple wiring or connector repairs are on the lower end, while component replacement costs more. A proper diagnosis ($80–$150 at most shops) will identify the exact cause before committing to expensive parts.

What To Do Next

Possible Fixes

🔧 Repair broken wire or restore ground in Brake Booster Motor A Position Sensor Supply circuit
🔧 Clean and secure Brake Booster Motor A Position Sensor Supply connector and ground points
🔧 Replace failed Brake Booster Motor A Position Sensor Supply

1
Find your vehicle above
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2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
3
Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.

C05B9: Brake Booster Motor A Position Sensor Supply Circuit Low