P0179
PowertrainSensormoderate severityFuel Composition Sensor Circuit High
What P0179 Means
The PCM detects a high voltage signal from the fuel composition (flex fuel) sensor circuit. The sensor reading is out of range on the high side.
Symptoms
- Check engine light on
- Poor performance on flex fuel
- Reduced fuel economy
Common Causes
- Faulty flex fuel sensor
- Short to voltage in wiring
- Open circuit
- Faulty PCM
Diagnostic Steps
- Scan for stored codes and freeze frame
- Check flex fuel sensor signal voltage
- Inspect wiring for shorts to power or opens
- Replace fuel composition sensor if faulty
🔌 Don't have a code reader?
Any of these will read and clear this code — pick by how deep you want to go.
Budget handheld~$40
ANCEL AD410 →
No-phone-needed handheld — reads, clears, live data, freeze frame.
✓ ANCEL official store
Serious DIY~$100
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Autel MaxiCOM MK808S →
Bidirectional tests, service resets, all systems.
✓ Autel official store
Pro diagnostics$1,500+
Autel MaxiSys MS906 Pro →
Full-system pro platform — topology mapping, ECU coding, the works.
✓ Autel official store
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