Fuel Composition Sensor Circuit High Input
The P0179 code indicates that the Engine Control Module (ECM) has detected a voltage signal from the fuel composition sensor that is higher than the expected range. This sensor monitors the ethanol content in the fuel, typically used in flex-fuel vehicles. A high input suggests a short to voltage, a faulty sensor, or a wiring issue. This can cause incorrect fuel mixture calculations, leading to performance problems.
01. Most Common Causes
- Faulty fuel composition sensor
- Short to voltage in sensor circuit
- Damaged wiring or connector
- Corroded terminals
- ECM issue (rare)
02. Symptoms You Will Notice
- Check Engine Light on
- Poor fuel economy
- Rough idle or hesitation
- Decreased engine performance
- Possible hard starting
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm P0179 and check for other codes.
Step 2: Visually inspect the fuel composition sensor and its wiring for damage or corrosion.
Step 3: Test the sensor's voltage signal with a multimeter; compare to manufacturer specs.
Step 4: Check for shorts to voltage or ground in the circuit.
Step 5: If sensor and wiring are okay, test the ECM's input circuit.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can cause poor performance and fuel economy, and may lead to further damage.
How much does it cost to fix?▼
Typically $50-$150 for diagnosis and sensor replacement, but costs vary by vehicle and labor rates.