P0178
Fuel Composition Sensor Circuit Low Input
The flex-fuel composition sensor signal is below the minimum threshold. Likely shorted to ground, open circuit or failed sensor.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Signal wire shorted to groundCommon
- Sensor failedPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Flex Fuel Composition Sensor
- Sensor Wiring
P0178 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.