P0119 is an engine code that points to a problem with your engine coolant temperature (ECT) sensor signal being intermittent or unstable. In plain terms, your car’s computer is seeing the coolant temperature jump around in a way that doesn’t make sense. That can affect cold starts, fuel mixture, and even when your cooling fans turn on. If you’ve got a check engine light and a P0119 stored, you’ll want to deal with it soon to avoid poor drivability, bad fuel economy, or in worst cases, overheating.
What Does P0119 Mean?
P0119 stands for “Engine Coolant Temperature Sensor Circuit Intermittent.” Your ECU constantly monitors the ECT sensor to know how hot the engine is. With this code, the ECU is seeing the voltage from that sensor jump or drop unexpectedly, or it’s losing the signal briefly and then getting it back.
This is different from a simple “too high” or “too low” temperature reading. P0119 focuses on signal stability. That’s why it often points to wiring issues, loose connectors, or a failing sensor that cuts in and out rather than a simple overheating condition.
Quick Reference
- Code: P0119 – Engine Coolant Temperature Sensor Circuit Intermittent
- Severity: Moderate – can lead to drivability issues and potential overheating
- Common Causes: Bad ECT sensor, wiring/connector issues, poor grounds, low coolant
- Typical Symptoms: Hard cold starts, rich running, erratic temp gauge, cooling fan issues
- Fix Difficulty: Moderate DIY for most vehicles with basic tools
Real-World Example / Field Notes
In the shop, I often see P0119 on vehicles that come in with a complaint like “temperature gauge goes crazy” or “fans run all the time.” One case was a mid-2000s sedan that would start fine some days and crank forever on cold mornings. Scan data showed the coolant temperature jumping from -40°F to 220°F instantly with the engine off. The problem ended up being a corroded ECT connector full of green crust. Cleaning and replacing the connector pigtail fixed the intermittent signal and cleared P0119 without needing a new sensor.
Symptoms of P0119
- Check engine light illuminated, often with no obvious drivability problem at first.
- Hard cold starts or extended cranking when the engine is cold.
- Rough idle after startup, especially in cold weather, sometimes with black exhaust smoke.
- Poor fuel economy because the ECU may think the engine is colder than it is and enrich the mixture.
- Erratic temperature gauge readings that jump up and down or stay cold.
- Cooling fans running constantly or not turning on when they should.
- Occasional stalling during warm-up or when shifting into gear.
- Other coolant temperature codes stored alongside P0119.
Common Causes of P0119
Most Common Causes
- Faulty ECT sensor: Internal failure causes intermittent resistance changes and unstable voltage output.
- Damaged wiring to the sensor: Broken, rubbed-through, or shorted wires near the sensor or harness.
- Loose or corroded connector: Poor contact at the ECT plug leads to signal dropouts when the engine moves or vibrates.
- Poor ground or reference voltage issues: Shared grounds or 5V reference circuits with other sensors can cause intermittent readings.
- Low or contaminated coolant: Air pockets around the sensor or incorrect coolant level can confuse the temperature reading.
Less Common Causes
- Thermostat problems: Stuck-open or stuck-closed thermostat can create odd temperature patterns that trigger related codes, though usually not P0119 alone.
- ECU internal fault: Rare, but a failing engine control module can misread a good sensor signal.
- Previous wiring repairs: Poorly done splices, butt connectors, or aftermarket remote start installations can cause intermittent circuits.
- Coolant sensor adapter or housing issues: On some engines, a cracked plastic housing or adapter can leak or move, affecting sensor contact with coolant.
- Incorrect sensor installed: Wrong part number or aftermarket sensor with out-of-spec resistance curve can appear “intermittent” to the ECU.
Diagnosis: Step-by-Step Guide
You’ll want a basic tool kit, a quality scan tool (ideally with live data and Mode $06), a digital multimeter, and possibly an infrared thermometer. Access to a wiring diagram for your specific vehicle helps a lot. Always start diagnosis with a cool engine to avoid burns and to see how the sensor behaves from a cold start.
- Confirm the code and check for others. Scan for DTCs and note any related codes like P0115–P0118. Multiple sensor codes can point to a shared power or ground issue, not just the ECT sensor.
- Check coolant level and condition. With the engine cold, verify the coolant is at the proper level and looks clean. Low coolant or heavy rust/sludge can cause poor sensor contact with coolant.
- Inspect the ECT sensor and connector. Locate the sensor (usually near the thermostat housing or cylinder head). Look for broken tabs, coolant leaks, green corrosion, oil contamination, or loose pins at the connector.
- Wiggle test with live data. Watch coolant temperature on the scan tool with the key on, engine off. Gently move the harness and connector. If the reading jumps suddenly (for example, from 70°F to -40°F or 300°F), you likely have a wiring or connector issue.
- Compare scan data to actual temperature. Use an infrared thermometer on the thermostat housing or cylinder head and compare to the ECT reading. A cold engine should read close to ambient temperature. Large discrepancies indicate a sensor or wiring fault.
- Check sensor resistance. With the connector unplugged and engine cool, measure resistance across the ECT sensor terminals. Compare to a temperature–resistance chart for your vehicle. Heat the engine slightly and recheck; resistance should change smoothly, not jump.
- Verify 5V reference and ground. With the key on, backprobe the connector. One terminal should have around 5V, the other should be a good ground or signal return. A missing 5V or floating ground points to a harness or ECU issue.
- Inspect wiring back to the ECU. If voltage and ground are unstable, trace the harness. Look for chafing against brackets, exhaust components, or sharp edges. Repair any damaged sections with proper solder/heat-shrink or OEM-style connectors.
- Check Mode $06 data (if available). Some scan tools show ECT monitor test results. This can confirm intermittent failures that don’t happen all the time and help verify your fix after repairs.
- Clear codes and perform a road test. After repairs, clear the code, start from a cold engine, and monitor ECT readings during warm-up and a short drive. Make sure the temperature rises smoothly and P0119 does not return.
Pro tip: If your scan data shows the ECT sensor stuck at exactly -40°F or 284–300°F, that’s usually a sign of an open or shorted circuit, not a real temperature. Focus on wiring and connectors before blaming the thermostat or coolant.
Possible Fixes & Repair Costs
Most P0119 repairs are straightforward once you pinpoint the issue. Common fixes include replacing the ECT sensor, repairing or replacing the connector pigtail, fixing damaged wiring, or correcting coolant level and bleeding air from the system. In rare cases, the ECU or thermostat housing may need replacement.
- Replace ECT sensor: $20–$80 for the part, $80–$200 labor depending on access.
- Repair/replace connector or pigtail: $20–$60 parts, $80–$180 labor.
- Wiring repair: $50–$200 depending on how deep into the harness the damage is.
- Coolant flush and bleed: $80–$180 at most shops.
- ECU replacement/programming (rare): $400–$1,000+ depending on vehicle.
Typical total repair costs for P0119 at a professional shop fall in the $150–$450 range when it’s just the sensor or connector. Costs go up if there are multiple issues, difficult access, or if overheating damage has occurred. Labor rates, vehicle design, and parts quality (OEM vs aftermarket) all affect the final bill.
Can I Still Drive With P0119?
You can usually drive short distances with P0119, but it’s not something you should ignore for long. The ECU may default to a “safe” temperature value, which can cause rich fuel mixtures, poor fuel economy, and rough running. More importantly, if the ECU doesn’t know the real coolant temperature, it may not control the cooling fans correctly, increasing the risk of overheating. If you notice the temperature gauge acting strange, fans running constantly, or any signs of overheating, avoid driving and get it checked immediately.
What Happens If You Ignore P0119?
Ignoring P0119 can lead to long-term issues like carbon buildup from rich running, fouled spark plugs, damaged catalytic converters, and potential overheating if the fans don’t operate correctly. Overheating can warp cylinder heads or blow head gaskets, turning a simple sensor or wiring repair into a very expensive engine job.
Related Codes
- P0129 – Barometric Pressure Too Low
- P0127 – Intake Air Temperature Too High
- P0126 – Insufficient Coolant Temperature for Stable Operation
- P0125 – Insufficient Coolant Temperature for Closed Loop Fuel Control
- P0124 – Throttle/Pedal Position Sensor/Switch “A” Circuit Intermittent
- P0123 – Throttle/Pedal Position Sensor/Switch “A” Circuit High
- P0122 – Throttle/Pedal Position Sensor/Switch “A” Circuit Low
- P0121 – Throttle/Pedal Position Sensor/Switch “A” Circuit Range/Performance
- P0120 – Throttle/Pedal Position Sensor/Switch “A” Circuit
- P0116 – Engine Coolant Temperature Circuit Range/Performance
Key Takeaways
- P0119 means your ECU is seeing an intermittent or unstable signal from the engine coolant temperature sensor.
- Most problems are caused by a bad sensor, corroded connector, or damaged wiring rather than a major engine issue.
- Symptoms range from a simple check engine light to hard starts, poor fuel economy, and erratic temperature readings.
- Diagnosis focuses on live data, wiggle testing the harness, checking resistance, and verifying 5V reference and ground.
- Repairs are usually affordable if handled early; ignoring the code can lead to overheating and expensive engine damage.
Vehicles Commonly Affected by P0119
P0119 can show up on almost any OBD-II vehicle, but it’s more frequently seen on certain brands and engine families. In my experience, it’s common on GM vehicles (Chevrolet, GMC, Buick, Cadillac) with aging plastic sensor connectors, as well as Ford and Lincoln models where harness chafing is an issue. Many Toyota, Lexus, Honda, and Acura vehicles can set this code when coolant connectors corrode or aftermarket sensors are installed. It’s also seen on Hyundai, Kia, Nissan, and various European brands, especially on higher-mileage cars and trucks where heat and vibration have taken a toll on wiring and connectors.
FAQ
Can P0119 cause my car not to start?
Yes, in some cases. If the ECU thinks the engine is extremely cold or extremely hot due to a bad ECT signal, it can command the wrong fuel mixture and cause hard starting or extended cranking, especially on cold mornings.
Is P0119 serious enough to fix right away?
It’s not as critical as an active overheating condition, but you should address it soon. An inaccurate coolant temperature reading can lead to poor drivability, wasted fuel, and eventually overheating if the fans don’t operate correctly.
Can I just replace the thermostat to fix P0119?
Usually, no. P0119 is about an intermittent sensor circuit, not just temperature being too low or too high. A bad thermostat can cause related codes like P0128, but P0119 is more often caused by the ECT sensor, connector, or wiring problems.
How do I know if it’s the sensor or the wiring?
Use a scan tool and multimeter. If wiggling the connector or harness makes the temperature reading jump, wiring or connector issues are likely. If the wiring tests good and the sensor resistance doesn’t match the actual temperature or changes erratically, the sensor is the prime suspect.
Can a low coolant level trigger P0119?
It can contribute. If the sensor is not fully submerged in coolant or there are air pockets in the system, the reading can fluctuate and appear intermittent. Always correct coolant level and bleed air before diving deep into electrical diagnosis.