Coolant Sensor and level questions

[Recoil Rob]

My 97 SR5 V6 has the CHECK ENGINE light on. After I reset the ECU by disconnecting the battery and then restarting the light was off for about 5 minutes and came back on. My local station plugged their diagnostic into it and he tells me the Coolant Temp Sensor is bad or the level is low.

It doesn't run hot, temp gauge always below the mid-point. The radiator is full when cold but I never see any fluid in the reservoir, hot or cold.

What's the proper level for the reservoir when cold?

I assume this is the ECU coolant sensor that is under the passenger side fuel rail? Any videos about doing this? I can't find any for the V6


thanks,

Rob

 

[TheDurk]

It would be better if you posted the exact P-code the scanner reported (in the form PXXXX). It's probably a P0125, and that is rarely a problem with the ECT. It is usually an O2/AF sensor issue (O2 in your case being a '97).

 

[Recoil Rob]

I'll try to get the exact code but I saw the diagnostic screen and it said Coolant Temp Sensor.

I was testing the truck after replacing the downstream sensor which was bad and while I was at it I cleaned the upstream with throttle cleaner spray.

 

[LittleCaesar]

It would have been better if you just bought a new Denso upstream O2 sensor to begin with because as Durk said, that is probably your culprit for the code. I hope the spray was O2 sensor safe.

 

[Recoil Rob]

OK, not doubting you but the last time I had it checked the code told me it was the downstream sensor so I replaced it with a Denso. Why would it now say it's the coolant sensor if it's still an O2 sensor?

I read here that sensors can be cleaned with Throttle body cleaner so I bought a can of GUNK throttle body cleaner. I just read the fine print which says not to spray on or around mass airflow sensors, is this the same as O2 sensors?

 

[Recoil Rob]

OK, I went back and got the following,

Code P0125

Insufficient Coolant
Temp Sensor for Closed Loop
Fuel Control

I also called GUNK and they said their throttle body cleaner is safe for O2 sensors.

thanks,

Rob

 

[JRZEE2000TR4LTD]

There's a graduation line on the reservoir bottle that says full hot (at least it does on my 2000) Generally the amount in the reservoir has more coolant in it when hot. If yours doesn't have any in it hot or cold, I would say your low on coolant and I would start there, before replacing sensors.

 

[TheDurk]

OK, not doubting you but the last time I had it checked the code told me it was the downstream sensor so I replaced it with a Denso. Why would it now say it's the coolant sensor if it's still an O2 sensor?

I read here that sensors can be cleaned with Throttle body cleaner so I bought a can of GUNK throttle body cleaner. I just read the fine print which says not to spray on or around mass airflow sensors, is this the same as O2 sensors?

Sometimes the ECU doesn't know what sensor is bad, it just knows either the ECT or the front O2 is wrong, and it sets P0125for some unknown reason (my personal theory). Most of the time it's the O2. Look at the FSM for P0125 below. The testing protocol is wrong on this because it's an a 2002 with an A/F but the fault tree logic is the same. Unfortunately, only the 2002 FSM is on-line. You will note the ECT is not even one of the possible causes listed.

Since the front usually fails before the rear, if you don't know the age of the front, it may well be time to change it. Or get a live scanner and look at the outputs of both, then decide. Do not just change the ECT unless you like wasting time and money.

 

[Recoil Rob]

Thanks Durk & All others,

Don't have access to a live scanner, will just replace fronts sensor. Since it was already out shouldn't be more than 10 Minutes.

Will try filling reservoir first though and report back.


thanks,

Rob

 

[TheDurk]

Thanks Durk & All others,

Don't have access to a live scanner, will just replace fronts sensor. Since it was already out shouldn't be more than 10 Minutes.

Will try filling reservoir first though and report back.


thanks,

Rob

No question that should be tried first, if level is indeed low.