What does the P0117 code mean?
The P0117 is a generic OBD-II (Onboard Diagnostics II) trouble code. Its official definition is “Engine Coolant Temperature Sensor Circuit Low Input“.
Background Information: This code is stored when the vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) detects that the voltage signal from the Engine Coolant Temperature (ECT) sensor is consistently lower than the expected normal operating range. The ECT sensor is a thermistor whose resistance decreases as coolant temperature increases. A “low input” typically corresponds to the ECM reading an implausibly high or hot temperature (often around 284°F or 140°C), which is most commonly caused by a short circuit to ground in the sensor signal path, a failed sensor with very low internal resistance, or a problem with the sensor’s 5-volt reference circuit. The first diagnostic step should always involve using a professional obd2 scanner to check the live ECT data, which will likely show a frozen or excessively high value.
Symptoms of Error Code P0117
- Illuminated Check Engine Light (MIL).
- Poor fuel economy, as the ECM may lean out the fuel mixture for a perceived hot engine.
- Engine hesitation, rough idle, or stalling during warm-up as fuel enrichment is insufficient.
- Difficulty starting, especially when the engine is actually cold.
- Engine may run cooler than normal or take a long time to warm up.
- Black smoke from the exhaust is less common than with P0118, but white smoke or overheating can occur if the fail-safe mode is inaccurate.
- The temperature gauge on the dashboard may show an excessively high reading or be pegged at hot.
Main Causes of Error Code P0117
- Faulty Engine Coolant Temperature (ECT) Sensor with an internal short circuit.
- Short Circuit to Ground in the Sensor Signal Wire (worn insulation touching chassis).
- Poor Electrical Connection or corrosion at the ECT sensor connector or ECM connector causing a voltage drop.
- Low or poor-quality engine coolant, or air pockets (air locks) in the cooling system causing erratic heat transfer to the sensor.
- Faulty PCM/ECM (rare) – internal fault in the signal processing circuit providing incorrect reference voltage.
- A stuck-open thermostat can contribute by preventing the engine from reaching normal operating temperature, confusing the system.
How to Diagnose Error Code P0117?
- Connect an OBD2 diagnostic scanner to confirm code P0117 and observe the live data stream for the ECT sensor. A reading stuck at 284°F (140°C) or an abnormally high value when the engine is cold confirms the issue.
- Check the engine coolant level and condition. Look for contamination or low level.
- Perform a visual inspection of the ECT sensor wiring harness (from sensor to ECM) and connectors. Look for pinched, frayed, or burned wires that could be shorting to ground.
- With the engine off and cool, disconnect the ECT sensor electrical connector.
- Using a digital multimeter, measure the resistance across the two terminals of the sensor itself. A very low or near-zero resistance reading indicates an internal short, failed sensor.
- Test the vehicle wiring harness:
- Check for 5-volt reference signal at the harness connector (with ignition ON). A low voltage here indicates a problem in the reference circuit.
- Check for a short to ground in the signal wire by measuring resistance between the signal pin and chassis ground. A very low resistance indicates a short.
Possible Causes and Diagnostic Methods
| Possible Cause | Diagnostic Test | Good Result / Faulty Result |
| Shorted ECT Sensor | Measure sensor resistance (disconnected). | Good: Resistance within spec (e.g., 2-3 kΩ at 68°F). Faulty: Very Low or 0-1 Ω. |
| Signal Wire Shorted to Ground | Check resistance between signal wire (disconnected from sensor) and chassis ground. | Good: High resistance (OL). Faulty: Very Low Resistance. |
| Low 5V Reference | Check voltage at harness connector with ignition ON. | Good: 4.5 – 5.0 V. Faulty: Significantly lower voltage. |
| Coolant/Air Pocket | Visual inspection, coolant system bleed procedure. | Good: Proper level, no air. Faulty: Low level or air in system. |
Tools needed: A quality OBD2 scanner (like an obd2 diagnostic tool or obd reader) capable of reading live data, a digital multimeter, basic hand tools, a cooling system pressure tester, and a vehicle-specific wiring diagram.
How do I fix error code P0117? (Solutions to the Problem)
Simple Fixes
- Repair shorted wiring by insulating the damaged section with electrical tape or heat-shrink tubing, or by replacing the wire segment.
- Clean corroded terminals at the sensor and ECM connectors with electrical contact cleaner and apply dielectric grease.
- Refill and properly bleed the cooling system to remove air pockets. Use the correct coolant mixture.
In-depth Diagnosis and Repair Solutions
- Replace the faulty ECT Sensor. Drain a small amount of coolant, install a new OEM-quality sensor, refill, bleed the system, and clear codes with your obd tool scanner.
- Repair or replace the damaged section of the wiring harness causing the short to ground.
- If the thermostat is stuck open, replace it to allow the engine to reach proper operating temperature.
- If all wiring and sensor tests are perfect, professional diagnosis of the PCM may be necessary.
Fix faults based on symptoms
| Symptom / Cause | Possible Solution | Critical Steps |
| Live data shows 284°F (Sensor Short) | Replace ECT Sensor. | Depressurize cooling system. Drain some coolant. Replace sensor. Refill and bleed system. Clear codes with obd2 diagnostic scanner. |
| Wire insulation damaged, short to ground found. | Repair wiring harness. | Locate the short. Splice in new wire section. Insulate properly. Re-test circuit. |
| Engine runs cool, takes long to warm up. | Replace thermostat. | Drain coolant, replace thermostat, refill and bleed system. |
| All tests pass, code returns. | Professional PCM/ECM test. | Verify 5V reference and signal input at PCM connector with an advanced scan tool. |
Common Error Code P0117 in Vehicles
Ford (F-150, Explorer, Expedition, Focus, Escape): Very common in models from the early 2000s to mid-2010s, particularly the 2003-2015 F-150 with the 4.6L, 5.4L Triton, and 3.5L EcoBoost engines. Wiring harness chafing and sensor failures are frequent.
Toyota/Lexus (Camry, Corolla, RAV4, Highlander, Tacoma, Tundra, Lexus ES/RX): A frequent code in models like the 2010-2015 Camry. Toyota sensors are generally reliable, but wiring issues and connector corrosion, especially in older vehicles, can trigger P0117.
Honda/Acura (Civic, Accord, CR-V, Odyssey, Pilot, Acura TL, MDX): Common, particularly in models from the late 1990s to early 2010s. The 2015-2018 Honda Civic is noted for this issue. Diagnosis benefits from a capable obd2 diagnostic scanner.
General Motors (Chevrolet, GMC, Buick, Cadillac): Common in trucks and SUVs like the Silverado, Tahoe, and Suburban, as well as passenger cars like the Impala and Malibu. The 2010-2015 Chevrolet Silverado is specifically reported.
Chrysler/Dodge/Jeep (Ram 1500, Grand Cherokee, Charger, 300, Wrangler): Often seen with the 3.6L Pentastar and 5.7L HEMI engines. Sensor failure or wiring issues are typical causes.
Nissan/Infiniti (Altima, Maxima, Sentra, Rogue, Pathfinder, Frontier, Infiniti G35/Q50): Frequent in models with the QR25 and VQ engine series. Sensor failure is a known issue.
Subaru (Impreza, WRX, Forester, Outback, Legacy): Common, sometimes associated with underlying cooling system problems (air pockets) or simple sensor failure.
Hyundai/Kia (Sonata, Elantra, Santa Fe, Sorento, Sportage, Optima): A very common code across many models, often solved by sensor replacement or checking for coolant air locks.
Volkswagen/Audi (Jetta, Golf, Passat, Tiguan, Audi A4, Q5): The ECT sensor (G62) is a common failure point. A short circuit in the wiring is a typical culprit.
BMW (3 Series, 5 Series, X3, X5): Can involve the sensor on the cylinder head or radiator outlet. Wiring issues and sensor shorts are not uncommon.
Mazda (Mazda3, Mazda6, CX-5, CX-9): Common in Skyactiv-G engines. The sensor or its circuit can develop a short.
P0117 Frequently Asked Questions
What is the first thing I should check with a P0117 code?
Use an OBD2 scanner to view the live Engine Coolant Temperature data. If it shows an implausibly hot reading (like 284°F/140°C) when the engine is cold or at ambient temperature, you have confirmed the fault. Then, inspect the sensor wiring for obvious shorts to ground.
Is it safe to drive with a P0117 code?
It is not advisable to drive for long. The engine will run in a lean “hot-engine” mode, which can cause poor performance, hesitation, stalling, and potential overheating if the fail-safe temperature setting is incorrect. Address it promptly.
How much does it typically cost to fix a P0117 code?
DIY repair: $20 – $80 for a new sensor. Professional repair at a shop: $70 – $330, including diagnosis and labor. Cost increases if wiring harness repair or a thermostat replacement is needed.
Can I replace the ECT sensor myself?
Yes, if you are comfortable working with engine coolant and basic hand tools. Remember to safely depressurize the cooling system, drain a small amount of coolant below the sensor level, and properly bleed the system of air after refilling. Use an obd reader to clear the code afterward.
Will disconnecting the battery clear the P0117 code?
It may temporarily clear the light, but the code and light will return on the next drive cycle if the underlying problem (like a short circuit) is not fixed. Use an obd2 diagnostic tool to clear codes only after a successful repair.
What’s the difference between P0117 and P0118?
P0117 is “Circuit Low Input” (low voltage/short to ground, reads as very HOT). P0118 is “Circuit High Input” (high voltage/open circuit, reads as very COLD). They are opposite electrical faults in the same sensor circuit.
Can a bad thermostat cause P0117?
Indirectly, yes. A stuck-open thermostat can prevent the engine from warming up properly. The ECM might see a discrepancy between expected warm-up time and the actual (but faulty) high temperature reading from a shorted sensor, but the code itself is for an electrical circuit fault.
My scan tool shows the ECT is 284°F. Is this definitely P0117?
Yes, a constant 284°F (140°C) reading is the classic symptom of a short circuit to ground in the ECT sensor circuit, which is precisely what triggers code P0117.
How do I test an ECT sensor for a short with a multimeter?
Disconnect it. Set the multimeter to Ohms (Ω). Measure resistance between the two terminals. A good sensor will show a specific resistance that changes with temperature. A very low or near-zero ohm reading means the sensor is internally shorted and faulty, causing P0117.
After replacing the sensor, the code came back immediately. Why?
The problem is almost certainly not the sensor, but in the wiring harness. You have a short to ground in the signal wire that you haven’t found and repaired yet. Inspect the entire wire run from sensor to ECM.
Do I need to bleed the cooling system after sensor replacement?
Yes. Anytime you open the cooling system and lose coolant, you must properly bleed it to remove air pockets. Air in the system can cause overheating, inaccurate gauge readings, and can even mimic or contribute to sensor circuit problems.
Is the ECT sensor the same as the temperature gauge sender?
Often, they are separate components. The ECT sensor provides data to the ECM for engine management. A separate temperature sender (often with one wire) typically feeds the dashboard gauge. Replacing the gauge sender will not fix a P0117 code.
Can a P0117 code cause overheating?
Yes. If the ECM’s fail-safe mode uses an incorrect temperature value, it may not activate the cooling fans at the right time, potentially leading to overheating, especially in stop-and-go traffic.
What tools are essential to diagnose P0117?
Essential tools: An OBD2 scanner capable of reading live data (an obd2 diagnostic scanner is ideal), a digital multimeter, basic hand tools, and a vehicle-specific wiring diagram for accurate circuit tracing.
Why is my engine running rough only when cold with a P0117 code?
The ECM thinks the engine is already hot (284°F), so it does not provide the extra fuel enrichment needed for a cold start. This causes a lean condition, leading to rough idle, hesitation, and stalling until the engine warms up on its own.
P0117 Related OBD2 Errors
- P0115: Engine Coolant Temperature Sensor Circuit Malfunction
- P0116: Engine Coolant Temperature Sensor Circuit Range/Performance Problem
- P0118: Engine Coolant Temperature Sensor Circuit High Input
- P0125: Insufficient Coolant Temperature for Closed Loop Fuel Control
- P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
- P2181: Cooling System Performance
Important! Always allow the engine to cool completely before attempting any work on the cooling system or ECT sensor to avoid the risk of severe burns from hot coolant or engine components. Diagnosing electrical shorts requires care to avoid causing further damage. If you are unsure about any diagnostic or repair procedure, consult a qualified automotive technician. Using a professional-grade obd2 diagnostic tool is highly recommended for accurate troubleshooting and live data monitoring.