The Flex Fuel Sensor, also known as an Ethanol Content Sensor, measures the composition of fuel in vehicles designed to run on ethanol blends, typically up to E85. This sensor analyzes the ethanol-to-gasoline ratio and sends that data to the vehicle’s engine control unit (ECU). Based on this input, the ECU adjusts ignition timing, fuel delivery, and air-fuel mixture to maintain optimal performance and emissions control regardless of fuel composition. Flex Fuel Sensors are crucial for ensuring the engine runs efficiently and cleanly whether the vehicle is using regular gasoline, ethanol, or any blend in between.
Common causes of Flex Fuel Sensor failure include:
• Fuel contamination or debris clogging the sensor
• Electrical circuit faults or damaged connectors
• Internal sensor corrosion due to high ethanol content
• Exposure to extreme temperatures or vibration
Symptoms of a failing Flex Fuel Sensor may include:
• Reduced engine performance or hesitation
• Hard starting, especially in cold weather
• Decrease in fuel efficiency
• Check Engine Light illuminated
• Inaccurate fuel mixture adjustments or poor throttle response
The following OBD II error codes are the most commonly found with this product type. In an effort to reduce vehicle emissions, the Environmental Protection Agency (EPA) mandated that all vehicles manufactured after 1996 be equipped with OBD II (On-Board Diagnostics 2) technology. OBD II is now the standard in diagnosing vehicle emissions and system faults, and is implemented across all automotive manufacturers. The codes listed for this product type are common instances that may relate to your vehicle and should be used as a guide only. Walker Products will not be held responsible for any use of this information. It is highly suggested that you consult with a professionally trained mechanic prior to any automotive repair, and that you follow all vehicle manufacturer and EPA guidelines for removal, replacement, diagnostics, OBD II code clearing, ECU, and PCM relearn procedures.
o P0178 Fuel Composition Sensor Circuit Low Input
o P0179 Fuel Composition Sensor Circuit High Input
o P0180 Fuel Temperature Sensor A Circuit
o P0181 Fuel Temperature Sensor A Circuit Range/Performance
o P0182 Fuel Temperature Sensor A Circuit Low
o P0183 Fuel Temperature Sensor A Circuit High
o P0184 Fuel Temperature Sensor A Circuit Intermittent