What happens when the coolant temperature sensor goes bad on a Chevy?
A bad coolant temperature sensor on a Chevy can trigger hard starting, rough idle, poor fuel economy, erratic temperature readings, and even overheating or heater issues.
The coolant temperature sensor (CTS) tells the engine computer how hot the coolant is, which governs fuel delivery, ignition timing, and cooling fan operation. When the CTS fails, the PCM can misread temperature, leading to a cascade of performance and efficiency problems. This article explains the signs, typical causes, how to diagnose them, and what repair may look like for Chevy models.
Symptoms and signs to watch
Below is a snapshot of the most common indicators that a Chevy’s CTS may be failing. These symptoms can appear individually or in combination, and some may be caused by related issues such as wiring or thermostat faults.
- Hard starting or extended cranking, especially when cold or after long stops
- Rough idle or misfires, particularly during warm-up or idling
- Poor or fluctuating fuel economy
- Erratic or non-linear temperature gauge readings on the dash
- Engine performance issues such as hesitation or reduced power
- Cooling fans cycling on and off at odd times or running continuously
- Heater not warming properly or, conversely, hot air blowing aggressively
- Check Engine Light with related codes (for example P0115–P0118)
Note: these symptoms can overlap with thermostat, wiring, or PCM issues. A proper diagnostic check is needed to confirm CTS failure.
What can cause these symptoms and how it affects the system
Several failure modes can produce the same signs, and understanding them helps guide diagnosis and repair. This section highlights the most common culprits beyond a faulty sensor itself.
- CTS stuck open (reads cold all the time) — PCM thinks the engine is cold and may over-enrich fuel mixture, wasting fuel and causing rough cold starts.
- CTS stuck closed or reading hot (reads hot all the time) — PCM assumes the engine is hot, may lean out fuel, raise ignition timing, or trigger overheating concerns.
- Wiring or connector problems — corroded or damaged wires, bad grounds, or a loose plug can mimic a sensor fault and produce erratic readings.
- Thermostat interaction — a faulty thermostat or a thermostat-related fault can complement or mask CTS symptoms, complicating diagnosis.
- PCM/ECU concerns — a faulty control module can misinterpret CTS data or fail to process it correctly, though this is less common than sensor or wiring faults.
Because the CTS is tied to multiple vehicle systems (fuel, ignition, fans, and climate control), a failure can manifest in several areas. A professional scan with live data is often needed to distinguish CTS issues from related components.
Diagnostics and how technicians approach it
Diagnosing a suspected CTS problem typically involves reading trouble codes, inspecting wiring, and verifying sensor readings against actual coolant temperature. The goal is to confirm the sensor’s function before replacing it.
- Read codes with an OBD-II scanner to look for P0115–P0118 family codes and related thermostat or sensor circuit faults.
- Compare live data: observe the CTS value as the engine warms up and cools, and compare it to the engine’s actual temperature (via infrared or reference data).
- Inspect wiring and connectors for damage, corrosion, or poor grounding at the CTS harness and the PCM/engine bay ground points.
- Check for thermostat issues and cooling system integrity, including coolant level, leaks, and proper operation of the cooling fans.
- If the CTS test shows out-of-range resistance or voltage behavior, plan for sensor replacement and retest the system after installation.
Diagnosing CTS problems requires model-specific knowledge, as wiring harness layouts and sensor specifications can vary among Chevy trucks, SUVs, and cars. Always consult the service manual or a qualified technician for precise procedures.
Repair options and what to expect
Replacement is typically straightforward, but labor time and parts costs can vary by model and year. This overview outlines the general steps and considerations.
- Obtain the correct CTS for your Chevy model/year (some reflect a sensor sits near the thermostat housing; others have different mounting points).
- Disconnect the battery, locate the CTS, unplug the electrical connector, and remove the old sensor.
- Install the new CTS with proper torque, avoiding overtightening or thread damage; use a gasket or sealant if required by the service manual.
- Reconnect the wiring, refill or top off coolant if necessary, and bleed the cooling system to remove air pockets.
- Start the engine and monitor live data to ensure the new sensor reading tracks actual coolant temperature and the PCM’s fuel/fan behavior returns to normal.
Costs vary by vehicle and location. Typical parts costs are modest, while labor can range depending on accessibility. Expect a total bill that reflects both parts and shop time; many Chevy CTS replacements fall into a mid-range ballpark, but always obtain a written estimate before service.
Summary
The coolant temperature sensor is a small but essential part of Chevy’s engine management, signaling the PCM about how hot the engine is to regulate fuel, ignition, and cooling fans. When it goes bad, symptoms range from hard starting and rough idle to poor fuel economy, erratic gauges, and potential overheating. Diagnostic steps focus on verifying sensor readings against real temperatures, inspecting wiring, and ruling out thermostat or PCM issues. Replacement is straightforward in most cases, with a typical repair path including sensor replacement, coolant system check, and re-testing to ensure proper operation. If you’re unsure about performing the work yourself, a qualified technician can diagnose and replace the CTS to restore proper engine performance and efficiency.
How much does it cost to replace a coolant temperature sensor?
The total cost to replace an engine coolant temperature sensor typically ranges from $70 to $330, with the sensor part costing between $15 and $80 and labor costing anywhere from $50 to $250. The exact price depends on your vehicle's make and model, the specific sensor's brand, and whether you perform the work yourself or hire a mechanic.
This video shows how to replace the engine coolant temperature sensor: 53s8020 AutomotiveYouTube · Mar 2, 2025
Part cost
- Sensor cost: The part itself is generally inexpensive, costing between $15 and $80.
Labor cost
- Mechanic installation: Hiring a professional adds to the total cost. Labor typically ranges from $50 to $250, but can be higher depending on your location and shop rates.
- DIY replacement: If you have basic mechanical knowledge and tools, you can replace the sensor yourself to save on labor costs.
Factors that influence the total cost
- Vehicle model: The complexity and labor time needed vary by car. Some sensors are easy to access, while others may require more time to reach.
- Shop rates: Local labor rates can cause significant price differences.
- Part quality: The brand and type of sensor you choose will affect its price.
- Additional repairs: The cost can increase if the repair involves other components, like draining and refilling coolant or removing other parts to access the sensor.
What happens if a coolant temperature sensor is bad?
While it's possible to drive with a failing coolant temperature sensor, it's not recommended. A faulty sensor can cause incorrect fuel mixture readings, overheating, and poor engine performance, leading to potential long-term engine damage.
What happens if I unplug the coolant temperature sensor on my Chevy?
In summary, unplugging the coolant temperature sensor can disrupt the engine's ability to adjust fuel and ignition timing properly, leading to potential misfiring, rough idling, and poor performance.
How to tell if your coolant temperature sensor is bad on a Chevy?
Symptoms of a Bad Coolant Temperature Sensor
- Overheating Engine. If you notice that your engine overheats, the coolant temperature sensor could be the problem.
- Poor Fuel Economy.
- 'Check Engine Lights Turns On.
- Black Smoke Emitted from the Engine.
- Poor Idling.
- Defective Electrical Cooling Fans.
