Will not start

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Since the problem is when it is cold, my first suspect is a bad engine coolant temperature sensor. This sensor sends a signal to the car's computer telling it the coolant's temp. With that information, the computer adjusts the air fuel mixture so the engine runs in specific temps. If the sensor has failed and is telling the computer it is 120°F, he fuel mixture may be too lean. Also, since the sensor is sending a signal, right or wrong, the computer doesn't know it is wrong and thinks things are working. Thus, the check engine light doesn't turn on.

Take a look through these links:

https://www.2carpros.com/articles/how-a-coolant-temperature-sensor-works

With this in mind, what needed to check it is a live data scanner. With that, you can see the actual temperature the sensor is telling the computer and determine if it is accurate.

IF you find it is bad, here are the directions for replacement. The attached pictures correlate with these directions. Picture 2 shows location.

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ENGINE COOLANT TEMPERATURE (ECT) SENSOR REPLACEMENT

REMOVAL PROCEDURE


picture 1

1. Turn ignition OFF.
2. Disconnect the ECT sensor harness connector.

IMPORTANT: Engine coolant must be drained below the level of the engine coolant temperature sensor (ECT) sensor. Refer to Draining and Filling Cooling System in Cooling System. See: Cooling System > Removal and Replacement

3. Remove the ECT.

INSTALLATION PROCEDURE


picture 1

1. Apply thread sealant SA P/N 21485277 Loctite 242(R) Threadlocker (or equivalent) to sensor threads.

IMPORTANT: Tap out sensor mounting hole in engine head to remove any thread sealant residue. Clean any sealant residue from old sensor and apply RTV sealant to threads if old sensor is going to be reused.

2. Install the ECT sensor with a new O-ring.

NOTE: Refer to Fastener Notice in Service Precautions.

Tighten the engine coolant temperature sensor to 18 N.m (13 lb ft).

3. Connect the ECT sensor harness connector. Push in the connector until a click is heard, then pull back to confirm a positive engagement.
4. Fill engine coolant to proper level. Refer to Draining and Filling Cooling System in Cooling System. See: Cooling System > Removal and Replacement

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If that checks good, considering the mileage, you may want to check engine compression when the engine is cold. The colder the engine gets, the more the engine block (metal) contracts. If the compression is low enough in those conditions, it won't start.

Here are a few links that discuss engine compression and how to check it:

https://www.2carpros.com/articles/symptoms-of-low-compression

https://www.2carpros.com/articles/the-reasons-for-low-compression

https://www.2carpros.com/articles/how-to-test-engine-compression

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Here are the directions specific to your vehicle for testing compression. The specs are included in the directions.

ENGINE COMPRESSION TEST
Engine Compression Test

^ Tools Required
- SA9127E Gage Bar Set

picture 3

1. Warm up the engine to a normal operating temperature of 98°C (208° F).
2. Turn the ignition switch OFF.
3. Remove the ignition coils.
4. Remove the spark plugs.
5. Attach the adapter (1), hose (2) and compression gage (3) to a spark plug hole.
6. Connect a tachometer.
7. Connect the scan tool.
8. Turn the ignition switch to the ON position.
9. Using the scan tool, command the injectors all off.
10. Depress the accelerator pedal to open the throttle fully.
11. Crank the engine with the starter motor and measure the compression.
12. Perform the measurement on each cylinder and compare the readings.
^ Compression pressure: minimum 990 kPa (145 psi) at 200 RPM
^ Maximum compression variation: 200 kPa (28 psi)
13. If the compression is not within specifications, inspect for the following conditions and measure the compression again.
^ Improperly adjusted valves
^ Improperly positioned timing belt and sprockets
^ Damaged or worn valves or seats
^ Damaged cylinder head gasket
^ Damaged or worn piston rings
^ Damaged or worn piston and cylinder bore
14. Using the scan tool, perform the PCM Reset Procedure to return the fuel injectors to normal operation.

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Compression must be a minimum of 145psi. If it drops below that when it's cold outside, you will have trouble starting it. Also, please understand, since you had this at a dealer, I am assuming the fuel pressure and spark were tested under the no start conditions. Here is one last link I want to add. It discuss a crank no start condition which you described. Take a look through it to see if everything has been covered by the dealer.

https://www.2carpros.com/articles/car-cranks-but-wont-start

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Let me know if this helps or if you have other questions.

Take care,
Joe

It still won’t stay running after we replaced that sensor.

Welcome back:

If the engine runs good warm, the sensors are all good, fuel pressure is within spec, and you have a good ignition spark at the plugs, I would then recommend checking engine compression when the engine is cold.

I attached directions in my first post. Try that and let me know what you find.

Joe