How to Change the Thermostat Sensor in a Chevy HHR

The Chevy HHR uses a coolant temperature sensor — sometimes loosely called a "thermostat sensor" — to monitor engine temperature and relay that data to the engine control module (ECM). When this sensor fails or reads incorrectly, you may see warning lights, erratic temperature gauge behavior, poor fuel economy, or rough running. Replacing it is a manageable DIY job on most HHR models, but the exact location and procedure depend on your engine, model year, and which sensor is actually at fault.

What the "Thermostat Sensor" Actually Is

There's an important distinction to make upfront. The HHR has two separate components that people often confuse:

• The coolant temperature sensor (CTS): An electronic sensor that reads coolant temperature and sends a signal to the ECM. This affects fuel trim, fan operation, and the temperature gauge.
• The thermostat itself: A mechanical valve inside a housing that opens and closes to regulate coolant flow. It doesn't send electrical signals but does contain a bleed hole and is seated in a housing that sometimes includes a temperature sensor port.

When people search "thermostat sensor," they usually mean one of these — or both, when the thermostat housing assembly includes a built-in sensor. On some HHR configurations, particularly those with the 2.2L Ecotec engine, the thermostat housing and sensor are closely positioned, which adds to the confusion.

HHR Engine Variants and What That Means for Location

The Chevy HHR was produced from 2006 to 2011 and came with two primary engine options:

The coolant temperature sensor on the 2.2L is typically located at or near the thermostat housing on the front of the engine, close to where the upper radiator hose connects. On the 2.0T, placement is similar but access points differ slightly due to the turbo and intercooler plumbing.

Knowing your exact engine code matters before buying parts or starting the job.

What You'll Need

• Replacement coolant temperature sensor (confirm fitment by engine and model year)
• Thread sealant or Teflon tape (if the replacement sensor doesn't come pre-coated)
• Socket set — typically a 19mm deep socket for the sensor itself
• Drain pan for coolant
• Fresh coolant to top off after the job
• Basic hand tools and a torque wrench if you want to follow spec

🔧 Some HHR owners report that sensor access is easier from below or with the engine cool. Working on a hot engine or pressurized cooling system is dangerous — always let it cool down fully before opening anything.

General Replacement Steps

1. Prepare the vehicle Park on a level surface, turn off the engine, and let it cool completely. Disconnect the negative battery terminal before working near any electrical connectors.

2. Drain or contain coolant You don't need to fully drain the system, but coolant will spill when the sensor is removed. Place a drain pan underneath. Partially draining the radiator until the level drops below the sensor location reduces the spill.

3. Disconnect the electrical connector The coolant temperature sensor has a small clip-style connector. Press the tab and pull straight back — don't yank by the wires. Set the connector aside safely.

4. Remove the sensor Using the correct socket, turn counterclockwise to unthread the sensor from the housing. Some resistance is normal, especially on older vehicles where the sensor may have been in place for years. Avoid excessive force that could crack the housing.

5. Install the new sensor If the replacement sensor doesn't include sealant on the threads, apply a thin layer of thread sealant or Teflon tape. Thread it in by hand first, then torque to spec — typically around 15 ft-lbs, though you should verify this for your specific engine. Over-tightening can crack the housing.

6. Reconnect the connector and refill coolant Snap the electrical connector back in place. Top off the coolant as needed. Reconnect the battery.

7. Start the engine and check for leaks Let the engine warm up and watch for any coolant leaks around the sensor. Verify the temperature gauge reads normally and that any warning lights have cleared.

Variables That Affect How This Job Goes

• Model year: Early HHRs (2006–2007) may have slightly different sensor thread sizes or housing designs than later models
• Engine condition: Corroded threads or a brittle housing can turn a 30-minute job into a much bigger one
• Whether the thermostat itself also needs replacement: If the housing is being removed anyway, many mechanics replace both the sensor and thermostat at the same time
• Access and clearance: Some HHR owners find the sensor easy to reach; others find coolant hoses and other components in the way depending on trim level and accessories

When It's Not Just the Sensor

If you've replaced the sensor and the temperature gauge is still reading incorrectly or the check engine light returned with a coolant temperature code (commonly P0117, P0118, P0128), the issue may lie elsewhere — a failing thermostat stuck open, a wiring harness problem, or an ECM issue. Code P0128 in particular often points to the thermostat itself rather than the sensor.

The sensor and thermostat are related components in the same system. A new sensor won't fix a mechanical thermostat that's stuck in the open position — and a new thermostat won't fix a sensor sending bad voltage signals.

Your specific HHR's condition, mileage, and diagnostic history are what determine which fix — or combination of fixes — actually resolves the problem.