P04B9 — Fuel Fill Door Position Sensor/Switch Circuit Low

What Does P04B9 Mean?

P04B9 is a diagnostic trouble code indicating: Fuel Fill Door Position Sensor/Switch Circuit Low. This code relates to the emission controls system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of P04B9

⚠️ Check Engine Light (MIL) illuminated
⚠️ Fuel Fill Door Position Sensor/Switch reading at zero or minimum value
⚠️ Related system not functioning or in fail-safe mode
⚠️ Failed emissions test

Common Causes

🔍 Open or broken wire in Fuel Fill Door Position Sensor/Switch circuit
🔍 Poor ground connection at Fuel Fill Door Position Sensor/Switch
🔍 Faulty Fuel Fill Door Position Sensor/Switch with no output signal
🔍 Disconnected or loose Fuel Fill Door Position Sensor/Switch connector
🔍 Blown fuse in related circuit

Frequently Asked Questions

What does P04B9 mean?

P04B9 indicates: Fuel Fill Door Position Sensor/Switch Circuit Low. The vehicle's computer has detected that the Fuel Fill Door Position Sensor/Switch is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code P04B9?

Yes, P04B9 is generally safe to drive with in the short term. However, it should still be addressed to pass emissions testing and prevent potential secondary issues.

How much does it cost to fix P04B9?

Repair costs for P04B9 typically range from $20 to $300, 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 Fuel Fill Door Position Sensor/Switch circuit
🔧 Clean and secure Fuel Fill Door Position Sensor/Switch connector and ground points
🔧 Replace failed Fuel Fill Door Position Sensor/Switch

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.

P04B9: Fuel Fill Door Position Sensor/Switch Circuit Low