P0176

What it means

P0176 is the generic SAE J2012 code for a fault in the fuel composition sensor circuit. This sensor, found on cars that run on petrol/ethanol blends, reports the ethanol content or fuel quality to the engine control unit. The code sets when the signal is missing, out of range, implausible or erratic, so the control unit cannot trust the fuel composition data.

Symptoms

• Engine warning light on
• Hard starting or extended cranking, especially when cold
• Rough idle or hesitation under load
• Poor fuel economy
• Engine running lean or rich, depending on the fuel in the tank
• Reduced performance if the control unit falls back to default fuelling

Possible causes

• Wiring or connector fault in the fuel composition sensor circuit (open circuit, short, corrosion or poor pin tension)likely
• Faulty fuel composition sensorlikely
• Contaminated or poor quality fuel, or an unexpected ethanol blend outside the sensor's rangepossible
• Water or debris in the fuel affecting sensor readingspossible
• Low or unstable supply voltage or poor earth to the sensorpossible
• Fault inside the engine control unitrare

How to diagnose

1. Read all stored codes and freeze frame data, and note any fuel trim, lean or rich codes stored alongside P0176
2. Ask when the car was last refuelled and with what fuel, and check for signs of contamination or water in the fuel
3. Visually inspect the sensor, its wiring and connector for damage, corrosion, fuel leaks, heat damage or chafing
4. Check the live data for the fuel composition or ethanol percentage reading and see whether it is plausible, fixed or erratic
5. Check the sensor supply, earth and signal wires against the manufacturer's wiring diagram, including continuity and short tests
6. Test the sensor output against the manufacturer's specification, as the signal type and location vary by model and engine
7. Check fuel trims and fuel quality to confirm whether the fuelling is being affected
8. Clear the code and road test to see if it returns after repairs

How to fix

• Repair or replace damaged wiring and clean or replace corroded connectors
• Replace the fuel composition sensor if it fails testing
• Drain and replace contaminated fuel, then clear the code and confirm it stays away
• Restore correct supply voltage or earth connections if they are found faulty
• Replace or repair the control unit only after all other causes are ruled out and the fault is confirmed

Can I keep driving?

Nearby codes

• P0175GenericSystem Too Rich Bank 2
• P0177GenericFuel Composition Sensor Circuit Range/Performance