Check engine light on a 2002 Toyota Corolla. What should I do?

engines

#1

I have a 2002 Toyota Corolla. On a hot day (the first in a while), I got a check engine light for P0125. I’m going to clear it and see if it comes back. I think it is a false alarm for insufficient engine coolant. If the code and check engine light come back, what should I do?


#2

P0125 TOYOTA - Insufficient Coolant Temperature for Closed Loop Fuel Control
Possible causes

  • Low engine coolant level
  • Leaking or stuck open thermostat
  • Faulty Engine Coolant Temperature (ECT) sensor
  • Engine Coolant Temperature (ECT) sensor harness is open or shorted
  • Engine Coolant Temperature (ECT) sensor electrical circuit poor connection

Read more: http://www.autocodes.com/p0125_toyota.html#ixzz4BxP49c3s


#3

Do something! Engine overheating can result in engine death!


#4

That fault indicates the engine is operating under the desired temperature. The thermostat is not closing all the way or the seal on the poppet valve in the thermostat has failed. Replace the thermostat before cool weather or next emissions test.


#5

Good one. Over heating is not happening on this vehicle, unless the thermostat changes its tune right way.


#6

This needs to be addressed since the engine computer will inject more gas with it thinking the engine coolant isn’t athe proper temperature. There’s two possible results, neither particularly good. First, the coolant is actually too cold, in which case you’ll get poor mpg, wasting money on extra gas purchases. Second, the coolant is the proper temp but the sensor is bad, in which case there’s the chance of extra gas coming out the exhaust manifold and going into the cat, which can damage the cat. Very expensive to repair.


#7

What is a typical cost of replacing the sensor? The problem has not happened again after I cleared the check engine light several days ago. I have driven a little each day.


#8

@Volunteer871

If you’ve done nothing except for clear the code, it WILL come back

First, check and correct the coolant level if necessary

Then replace the thermostat, bring coolant up to correct level. Run engine up to proper operating temperature, until TOASTY air comes out of panel registers. Recheck coolant level again

End of story


#9
What is a typical cost of replacing the sensor? The problem has not happened again after I cleared the check engine light several days ago. I have driven a little each day.

To clarify, OP, did you add coolant b/c it was low when you looked in the radiator? Then you cleared the code, and the code or CEL hasn’t come back? If so, I’d just drive on then, and check the dash cooling gauge and the coolant level each morning to see if it is dropping again. If it isn’t you are probably good to go.

If you continue to have problems, it’s more likely to be the thermostat than the engine coolant temperature sensor. Here’s an estimate for the parts and labor for each job.

Thermostat, $20 for the part and 1-2 hours labor.

Engine coolant temperature sensor (used by engine computer), $70 for the part, 1 hour labor.


#10

Six weeks ago the coolant level was fine. I need to check the coolant level. I did nothing and cleared it the code. It came back once. I cleared it again. It doesn’t seem to be coming back. But it probably will. I’ll take it to the mechanic. It sounds like the thermostat should be changed.


#11

I had a different vehicle for running too cool, throwing a code, barely noticeable on the temp gauge, new thermostat was my first kick at the cat, and it worked.