P0178
Fix within 1-2 weeksYour engine computer detects a low voltage signal from the fuel temperature sensor 'B' circuit. This means the computer sees an issue with how the fuel temperature sensor is reporting fuel temperature, often indicating the sensor believes the fuel is too hot, or there's an electrical problem.
Code P0178 means your engine computer detects a problem with the fuel temperature sensor 'B' circuit. Common causes: Faulty fuel temperature sensor (60%), wiring issues (30%). Drivability: Yes, safe to drive. Repair cost: $50-$150 DIY, $150-$350 professional.
Can I Drive With P0178?
Yes, safe to drive
No restrictions
Stop driving immediately if: Flashing Check Engine Light, significant power loss, or other severe drivability issues (which are rare for this code).
Symptoms of P0178
- 1Check Engine Light is on
- 2Reduced fuel economy
- 3Rough idle or poor engine performance (less common)
- 4Hard starting, especially when the engine is hot (less common)
Common Causes of P0178
Parts most likely causing this code, ranked by probability
The fuel temperature sensor itself has failed internally, sending an incorrect low voltage signal to the engine computer.
60% of P0178 cases are fixed by replacing this part
Damaged wires, corroded pins, or a loose connection in the fuel temperature sensor circuit can cause an incorrect voltage reading.
30% of P0178 cases are fixed by repairing wiring or connectors
A faulty engine computer can misinterpret the sensor's signal or fail to process it correctly, though this is a rare cause.
10% of P0178 cases are fixed by replacing the ECM/PCM
Check These First (Before Buying Parts)
- Visually inspect the fuel temperature sensor's wiring harness and connector for any signs of damage, fraying, or corrosion.
- Ensure the connector is securely seated on the sensor.
How to Diagnose P0178
- 1Visually inspect the fuel temperature sensor and its wiring harness for any obvious damage, fraying, or corrosion.
- 2Check the electrical connector at the fuel temperature sensor for loose pins, corrosion, or proper seating.
- 3Using a multimeter, test the resistance of the fuel temperature sensor (if accessible) and compare it to factory specifications.
- 4With a scan tool, monitor the live data for the fuel temperature sensor 'B' to see if the readings are erratic or stuck.
- 5If the sensor and wiring check out, test the voltage at the sensor connector to ensure the ECM is providing proper reference voltage.
P0178 on Popular Vehicles
Ford F-150
2004-2024While less common on gasoline F-150s, if present, the fuel temperature sensor is often integrated into the fuel pump assembly or located on the fuel rail. Wiring issues are a frequent culprit.
60% fixed by replacing the sensor, 30% by wiring repair
Chevrolet Silverado
2007-2024On Silverado models, especially those with diesel engines (Duramax), the fuel temperature sensor is typically found in the fuel filter housing or on the fuel rail. Corrosion at the sensor connector is a known issue.
60% fixed by replacing the sensor, 30% by wiring repair
Ram 2500/3500
2003-2024For Cummins diesel engines in Ram trucks, the fuel temperature sensor is crucial for fuel system management. It's often located near the fuel filter or on the fuel rail. Sensor failure or harness damage are the primary causes.
60% fixed by replacing the sensor, 30% by wiring repair
Frequently Asked Questions
What does P0178 mean?
P0178 indicates that the engine's computer is receiving a low voltage signal from the fuel temperature sensor 'B'. This suggests an issue with the sensor itself or its electrical circuit, often leading the computer to believe the fuel is hotter than it actually is.
Can I drive with P0178?
Yes, safe to drive. This code typically does not cause immediate drivability issues or severe damage. However, you should fix it within 1-2 weeks to restore proper fuel economy and engine performance.
Will P0178 clear itself?
No, P0178 will not clear itself. The Check Engine Light will remain on until the underlying fault with the fuel temperature sensor or its circuit is repaired and the code is manually cleared or the vehicle completes several drive cycles without the fault recurring.
How do I fix P0178 myself?
Start by visually inspecting the fuel temperature sensor and its wiring for damage or corrosion. If the wiring looks good, you can test the sensor's resistance with a multimeter. If the sensor is faulty, replacing the fuel temperature sensor 'B' is the most common fix.
How much does it cost to fix P0178?
The cost to fix P0178 ranges from $50-$150 for DIY, primarily for the sensor part. Professional repair costs typically range from $150-$350, covering parts and labor.
P0178 keeps coming back - why?
If P0178 keeps returning, it indicates the initial repair did not address the root cause. This often happens if the wiring or connector was overlooked, or if the engine computer itself has a rare internal fault. Double-check all electrical connections and consider professional diagnosis.
Will P0178 fail emissions/smog test?
Yes, P0178 will cause your vehicle to fail an emissions or smog test. Any active Check Engine Light indicates a fault in the emissions system, preventing the vehicle from passing inspection.
What's the difference between P0178 and P0179?
P0178 indicates a 'low input' from the fuel temperature sensor 'B' circuit, meaning the computer sees a voltage signal that is too low (often interpreted as too hot fuel). P0179 indicates a 'high input', meaning the computer sees a voltage signal that is too high (often interpreted as too cold fuel).
P0178 on Ford F-250/350 Powerstroke?
On Ford Powerstroke diesel engines (F-250/350), P0178 is often related to the fuel temperature sensor located in the fuel filter housing or on the fuel rail. These sensors are critical for proper fuel injection timing and emissions control in diesel systems. A faulty sensor or corroded connector in these locations is a common cause.
Questions to Ask Your Mechanic
Did you check the live data for the fuel temperature sensor 'B' with a scan tool?
Good answer: Yes, the live data showed the sensor was stuck at a high temperature reading, indicating a low voltage signal, which confirms the sensor or circuit fault.
What did you find when inspecting the wiring and connector for the fuel temperature sensor?
Good answer: I found some corrosion on the pins of the connector, or a section of the wire was chafed, causing an intermittent connection.
Repair Cost Estimate
DIY Repair
Parts only
$50-$150
Shop Repair
Parts + labor
$150-$350
Save $100-$200 by doing it yourself
Difficulty
intermediate
Time
0.5-2 hours
Intermediate - requires basic electrical diagnostic skills and tools like a multimeter and scan tool.
Cost of Waiting
Ignoring P0178 can lead to reduced fuel economy and potentially affect engine performance over time. While not immediately catastrophic, it can cause the engine computer to make incorrect fuel delivery decisions, leading to less efficient operation.
While You're In There...
On many vehicles, especially diesels, the fuel temperature sensor is located near or within the fuel filter housing. Replacing the fuel filter is routine maintenance and makes sense if you are already accessing that area.
Tools You'll Need
- OBD-II Scan Tool
- Multimeter
- Basic hand tools (wrenches, sockets)
- Wire strippers/crimpers (if wiring repair is needed)
P0178 is a common electrical code. Most repairs involve replacing an inexpensive sensor or fixing a simple wiring issue, and your vehicle will run efficiently again.
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Your Next Steps
Step 1: Perform a thorough visual inspection of the fuel temperature sensor 'B' and its entire wiring harness. Look for any cuts, chafing, or corrosion on the wires and connector pins.
Step 2: If the visual inspection doesn't reveal any issues, use a multimeter to test the resistance of the fuel temperature sensor itself. Compare your readings to the vehicle's service manual specifications. If the resistance is out of spec, replace the sensor.
Step 3: If the sensor tests good, use an OBD-II scan tool to monitor the live data for the fuel temperature sensor 'B'. If the reading is erratic or stuck, and the wiring is confirmed good, then the issue might be with the engine computer, though this is less common.