mikeurbas

My service engine soon light recently went on. I took it to a local auto parts store, and they hooked it up to there analyzer, and told me it was my thermostat. I still am getting hot air. How do o now its not a faulty sensor, and if its the thermostat is it the upper or lower? Any help would be greatly appreciated! Thanks, Mike.

petrock

There are no thermostat sensors, so I don’t know how they could determine that the thermostat is bad. The computer has no way of knowing. Go back to the store and get the exact trouble code, not just the description. It should be something like P1000. Then post up that code and we’ll see what we can do.

dawson1112

http://www.obd-codes.com/p0128

P0128 OBD-II Trouble Code

What does that mean?

This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat.

In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle
A code P0128 may mean that one or more of the following has happened:
•Low engine coolant level
• Leaking or stuck open thermostat
•Faulty cooling fan (running too much)
• Faulty coolant temperature (ECT) sensor
•Faulty intake air temperature (IAT) sensor

See also http://www.obd-codes.com/p0125

I was unaware that the newer mustangs had 2 thermostats, but if that's the case its probly best to change both..

Check coolant level first.
The new and better types of thermostats are designed so that if they fail they default to the open position so not to over heat the engine. This would trip a PO128 code. And I am guessing that is the code that they pulled at the place that scanned it.

petrock

Cool. I didn’t know about that code. But it makes sense. As it stated, there can be multiple reasons for this code to appear. I’d check the coolant level & condition first, then check out the fan to see if it is on too much. After that, only then would I dive into a new thermostat.


+1. Don’t skimp out of thermostats. You get what you pay for.

mikeurbas

Thanks for all the help everyone! I now realize it only has one thermostat. My problem is AutoZone's tester only gives general information. I guess I have to bite the bullit [pun intended]and take it to a mechanic to have them put it on there computer so I can see what code number I'm getting.

petrock

The mechanic will get the same codes AutoZone will (unless its a tranny code or ABS code). It sounds like the Autozone employee just told you the description of the trouble code. You need the actual trouble code which the employee can simply read to you off the scanner. Something like P0128, for example. I would go back to auto zone and get the actual code instead of just the description. You can then search the intertubes for what the code means and for possible fixes. Good luck...

WJBertrand

I wonder if the OBDII code found is coincidental? I think the "service engine soon" light is just an oil change reminder?

JimC

No, it isn't an oil change reminder!

A check engine light or service engine soon light means the ECU detected a problem. And you will pull the code to direct you to the issue(s)

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WJBertrand

So what's the difference between the "service engine soon" and "check engine" lights?

JimC

Different terms for the same thing. Different years have changed the terms over time.

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