P0117
Fix within 1-2 weeksThe engine computer detects a very low voltage signal from the Engine Coolant Temperature (ECT) sensor, indicating the engine coolant is extremely cold or there's an electrical problem in the sensor circuit.
Code P0117 means your engine coolant temperature sensor circuit has a low input. Common causes: Faulty ECT sensor (65%), wiring issues (25%). Drivability: Yes, but fix within 1-2 weeks. Repair cost: $50-$200 DIY, $150-$500 professional.
Can I Drive With P0117?
Yes, safe to drive
No restrictions, but fix within 1-2 weeks to prevent further issues.
Stop driving immediately if: Flashing CEL, engine overheating, significant power loss, or strong smell of raw fuel.
Symptoms of P0117
- 1Check Engine Light is on
- 2Engine runs rough, especially when cold
- 3Poor fuel economy
- 4Black smoke from the exhaust
- 5Hard starting, particularly in cold weather
- 6Engine may overheat (if the computer thinks it's always cold and doesn't activate cooling fans)
Common Causes of P0117
Parts most likely causing this code, ranked by probability
The sensor itself has failed internally, sending an incorrect low voltage signal to the engine computer.
65% of P0117 cases are fixed by replacing this part
A short to ground in the sensor's signal wire, or corrosion/damage in the connector, causes the low voltage reading.
25% of P0117 cases are fixed by repairing the wiring or connector
If the coolant level is too low, the sensor may not be fully submerged, leading to erratic or incorrect low temperature readings.
5% of P0117 cases are fixed by topping off coolant
A rare internal fault within the engine computer's ECT sensor input circuit can cause this code.
5% of P0117 cases are fixed by replacing the ECM/PCM
Check These First (Before Buying Parts)
- Check your engine's coolant level. Ensure it's full and clean.
- Visually inspect the ECT sensor and its electrical connector for any signs of damage, corrosion, or loose wires.
How to Diagnose P0117
- 1Check the engine coolant level and condition.
- 2Visually inspect the ECT sensor and its electrical connector for damage, corrosion, or loose connections.
- 3Use a scan tool to monitor the ECT sensor's live data; look for an impossibly low temperature reading (e.g., -40°F/-40°C).
- 4With the engine off, disconnect the ECT sensor and test its resistance with a multimeter, comparing to manufacturer specifications at ambient temperature.
- 5Check for proper reference voltage (typically 5V) at the ECT sensor connector with the key on, engine off.
- 6Test for continuity and shorts to ground in the ECT sensor wiring harness back to the ECM/PCM.
P0117 on Popular Vehicles
Honda Civic
2006-2024ECT sensor failures are common on these models. The sensor is usually located on the cylinder head or thermostat housing. Inspect the connector for corrosion.
70% fixed by replacing the ECT sensor
Toyota Camry
2007-2024Similar to Hondas, Toyota Camrys frequently experience P0117 due to a failing ECT sensor. Ensure the coolant level is correct before diagnosing the sensor or wiring.
65% fixed by replacing the ECT sensor
Ford F-150
2004-2024On Ford F-150s, P0117 can be caused by the ECT sensor, but also pay close attention to the wiring harness, especially where it might rub against other engine components, causing a short.
60% fixed by replacing the ECT sensor, 20% by wiring repair
Frequently Asked Questions
What does P0117 mean?
P0117 indicates that the engine's computer is receiving an abnormally low voltage signal from the Engine Coolant Temperature (ECT) sensor, suggesting the coolant is extremely cold or there's an electrical fault in the sensor's circuit.
Can I drive with P0117?
Yes, you can drive with P0117, but you should fix it within 1-2 weeks. The engine computer will likely assume the engine is always cold and run a rich fuel mixture, leading to poor fuel economy and potential damage to your catalytic converter over time.
Will P0117 clear itself?
No, P0117 will not clear itself. The underlying electrical or sensor fault must be repaired. Once the issue is resolved, the code can be cleared with a scan tool, or it will clear automatically after several drive cycles if the fault does not return.
How do I fix P0117 myself?
Start by checking your coolant level and visually inspecting the ECT sensor and its wiring for damage. If those look good, use a multimeter to test the resistance of the ECT sensor and check for proper voltage at its connector. If the sensor tests bad, replace it. If wiring is damaged, repair it.
How much does it cost to fix P0117?
DIY repair costs for P0117 are typically $50-$200, mainly for a new ECT sensor and possibly some coolant. Professional repair costs range from $150-$500, covering parts and 1-2 hours of labor.
P0117 keeps coming back - why?
If P0117 keeps returning, it means the root cause was not fully addressed. This often points to a persistent wiring issue (a short that wasn't found), a faulty replacement sensor, or a rare ECM/PCM problem. Thoroughly re-inspect the wiring harness and re-test the circuit.
Will P0117 fail emissions/smog test?
Yes, P0117 will cause your vehicle to fail an emissions or smog test. The Check Engine Light being on is an automatic failure, and the rich fuel mixture caused by this code will also result in higher emissions.
What's the difference between P0117 and P0118?
P0117 indicates an Engine Coolant Temperature (ECT) sensor circuit 'low input,' meaning the computer sees an impossibly low voltage (very cold temperature). P0118 indicates an ECT sensor circuit 'high input,' meaning the computer sees an impossibly high voltage (very hot temperature), often due to an open circuit or short to voltage.
P0117 on Honda Civic
P0117 on a Honda Civic often points directly to a faulty ECT sensor. These sensors are known to fail on various Honda models. Always check the wiring and connector first, but be prepared to replace the sensor itself, which is typically located near the thermostat housing.
Questions to Ask Your Mechanic
Did you check the live data from the ECT sensor with a scan tool?
Good answer: Yes, the scan tool showed the coolant temperature stuck at -40 degrees Fahrenheit, confirming a low input signal.
What did you find when you tested the ECT sensor's resistance and the circuit's voltage?
Good answer: The sensor's resistance was out of spec, or I found a short to ground in the signal wire, causing the low voltage.
Repair Cost Estimate
DIY Repair
Parts only
$50-$200
Shop Repair
Parts + labor
$150-$500
Save $100-$300 by doing it yourself
Difficulty
intermediate
Time
0.5-2 hours
Intermediate - While replacing the sensor is beginner-friendly, accurately diagnosing wiring issues and testing with a multimeter requires some intermediate skill and tools.
Cost of Waiting
Ignoring P0117 causes your engine to run rich, leading to significantly reduced fuel economy and potentially damaging your expensive catalytic converter. A $50-$80 sensor replacement now prevents a $1,200-$2,500 converter replacement later.
While You're In There...
If you're draining coolant to replace the sensor, it's a good time to flush and replace old coolant, especially if it's due for maintenance.
While not a direct cause of P0117, if your engine has been running cold or you suspect other cooling system issues, the thermostat is often in the same area and can be replaced with minimal additional labor.
Tools You'll Need
- OBD-II Scan Tool
- Multimeter
- Socket/Wrench Set
- Pliers
- Coolant Drain Pan
- Screwdriver Set
P0117 is a common sensor code, and the repair is usually straightforward. Most fixes involve replacing an inexpensive sensor, and your engine will run much better afterward.
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Your Next Steps
Step 1: Check your coolant level and visually inspect the ECT sensor and its wiring for any obvious damage or corrosion.
Step 2: Use an OBD-II scan tool to check the live data for the ECT sensor. If it reads an extremely low temperature (e.g., -40°F), proceed to electrical testing.
Step 3: Disconnect the sensor and use a multimeter to test the sensor's resistance and the voltage at the connector. Compare readings to your vehicle's service manual.