Honda Civic Coolant Temperature Sensor Guide (2002-2011)
Erratic temperature gauge, poor fuel economy, or a check engine light on your Civic could point to this simple, inexpensive sensor.
- A bad ECT sensor is a common cause for a check engine light with codes P0117, P0118, or P0128.
- Symptoms also include poor gas mileage, rough idle, and potential overheating if the cooling fans don't run.
- Replacement is a very simple DIY job that takes less than 30 minutes with basic tools.
- Before replacing, check your coolant level and consider if a faulty thermostat could be the real issue.
Is Your Civic's Coolant Temp Sensor Failing?
A bad coolant temperature sensor can cause a surprising number of problems. Because the car's computer relies on its signal for so many adjustments, a faulty sensor sending incorrect information can make the engine run poorly. You might notice one or more of the following issues.
Common Symptoms of a Bad ECT Sensor:
- Check Engine Light: The most common sign. You may see codes like P0117 (Circuit Low), P0118 (Circuit High), or P0128 (Cooling System Malfunction).
- Poor Fuel Economy: If the sensor tells the computer the engine is cold when it's not, the computer will enrich the fuel mixture, wasting gas.
- Rough Idle or Stalling: The wrong temperature reading can lead to incorrect idle speed control, making the engine run rough or even stall.
- Black Smoke from Exhaust: This is a sign of a rich fuel mixture, where the engine is getting too much gasoline and not enough air, often caused by a faulty ECT sensor reading cold.
- Engine Overheating: The 8th generation Civic (2006-2011) uses a second ECT sensor at the bottom of the radiator to control the cooling fans. If this sensor fails, the fans may not turn on when you're stopped in traffic, causing the engine to overheat.
- Erratic Temperature Gauge: The needle on your dashboard might jump around, read very high suddenly, or not move at all.
Check the Thermostat and Coolant Level First
Before replacing the sensor, always check two things. First, ensure your coolant level is correct; a low level can cause the sensor to read air instead of coolant, triggering a code. Second, a thermostat that is stuck open can prevent the engine from reaching its proper operating temperature, which can also trigger a P0117 or P0128 code. A new thermostat is often an inexpensive and wise repair to perform along with the sensor.
🎬 See how to diagnose and replace a stuck thermostat.Choosing the Right Aftermarket Sensor
For a vehicle in the 2002-2011 year range, using a quality aftermarket coolant temperature sensor is a perfectly reasonable choice. The original Honda (OEM) part is excellent but can be significantly more expensive. Aftermarket brands like NTK, Delphi, and Standard Motor Products offer reliable alternatives that function well for daily driving. Since this part is relatively cheap and easy to access, the risk of using an aftermarket brand is low. The key is to buy from a reputable source to avoid counterfeit or low-quality parts.
Cost Comparison: 2002-2011 Civic ECT Sensor
| Part Type | Estimated Cost |
|---|---|
| New OEM (Honda) | $45 - $70 |
| New Aftermarket (Replacement) | $20 - $40 |
| Shop Labor | $95 - $150 |
Pro Tip: A Quick and Easy DIY Job
🎬 Watch this step-by-step sensor replacement for 2001-2005 Civics.Replacing the ECT sensor is one of the easier repairs you can do on your Civic. It's typically a 15-30 minute job with basic tools. The main sensor (ECT 1) is located on the cylinder head, usually near where the upper radiator hose connects. The job simply involves unplugging the wire, unscrewing the old sensor, and quickly screwing the new one in. You will lose a small amount of coolant, so have a rag ready. Always perform this repair on a cold engine to avoid burns.
Known Issues for 2002-2011 Honda Civics
Technical Service Bulletin (TSB 09-092): For 2006-2009 Civics (excluding Si, Hybrid, and GX models), Honda issued a TSB for a Check Engine Light with code P0128. The problem was often the vehicle's software misinterpreting the sensor data. The fix involves a software update at a dealership. The bulletin also notes to check for corrosion on the connector for ECT sensor 2, which is located at the bottom of the radiator.
Frequently Asked Questions (FAQ)
Where is the coolant temperature sensor located on a 2002-2011 Civic?
Most Civics in this range have two sensors. The primary one (ECT 1), which affects engine performance, is on the cylinder head near the thermostat housing and upper radiator hose. The second one (ECT 2), which helps control the cooling fans, is screwed into the bottom of the radiator on the driver's side.
Can I drive my Civic with a bad coolant temperature sensor?
You can, but it's not recommended for long. You will experience poor performance, bad gas mileage, and potentially fail an emissions test. If the sensor is causing your cooling fans to not work, you risk serious engine damage from overheating.
What tools do I need to replace the sensor?
You'll typically need a deep socket and ratchet. Depending on the specific year and sensor, the size is often 17mm or 24mm. A pair of pliers for hose clamps and a rag for coolant spills are also helpful. Some owners find removing the battery makes access easier on certain models.
Do I need to drain the coolant to replace the sensor?
You don't need to drain the entire system. When you unscrew the sensor, a small amount of coolant will leak out. If you are quick to swap the old sensor for the new one, coolant loss will be minimal. Just be sure to top off the radiator with the correct Honda blue coolant afterward.
Helpful Videos
Technical Specifications
OEM Part Numbers: 37870-PLC-004 37870-PNA-003 37870-RTA-005
The primary ECT is a two-wire thermistor sensor typically located on the cylinder head. A secondary switch/sensor may be located in the radiator.
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Honda Civic: