So I posted in the Ecuflash section of the tuning forum and have had no luck with responses on this. So I'll try here. I recently changed my thermostat from what the previous owner had been running. He had installed a 63 degree stat and I replaced it with a OEM 83 degree stat. I wanted heat this winter. Now I have heat, car idles great and runs fine. But I keep getting the P0125 insufficient coolant temp for closed loop operation code. In the data list, when this code sets, I'm at 180 degrees and in closed loop. I have the tephra mod, no rear 02 reading. This is the only thing I changed, didn't mess with anything else, tune etc...., it ran fine before with no check engine light with the colder thermostat. Do I need to modify something in my tune to get rid of it? Thanks guys.

 

Have you cleared all previous codes from the ECU memory?

 

Yes, all codes have been cleared. Is there any other reset procedure? I'm using a Snap On Solus scanner right now for data observation till my Tactrix cable comes in next week. It takes about roughly 10miles or 15 mins of driving, depending on coolant temp when I start the car for the light to come back on. However, the freeze frame data shows I'm in closed loop when the code sets and temp is at 176 to 182 degrees.

 

If the codes have been cleared with the scanner, I wouldn't expect to see that. As you have changed the T-stat, which means the connection to the coolant switch has been disturbed, the obvious suspect is a flaky electrical connection at that sensor, which if intermittent, could cause what you are witnessing. Be sure that connection is solid and secure, as this would explain why you didn't get the code before, and are getting it now.

 

I'll double check the connection, but would that allow a consistent reading by the ECM to show me on the scanner a value for the coolant temp sensor? I would think if the connection was messed up that I would see the value screw up from time to time in the data list.

 

I don't know what the data log will or won't show, but even a momentary blip in the connection is enough to throw a code and keep it in memory. The OE manual attributes that code to one of three things: (1) Poor connection, (2) Bad sensor, (3) ECU issue.

Again, I would remove and check that connection, which is on the backside of the T-stat. The single wire connector on the front side is for the gauge only. If in doubt replace the sensor. Also, be sure you've run the engine long enough with the radiator cap off to bleed any trapped air from the T-stat area. This is a common pitfall of servicing the coolant system. Another thing you can try is reflashing your program into the ECU, which has solved strange behavior in my case once or twice.

 

I checked the connection yesterday, both pins are straight and both terminals are locking tightly around them. I added some dielectric grease to the connector to be sure I was getting a good connection, no luck, code still came back on while I was on my way home. I can try and replace the sensor if a reflash doesn't help. It's just weird that the only thing I changed was the thermostat and now this is happening. Thanks for all the suggestions.

 

If you are certain that you've bled the coolant system to eliminate air pockets, then reflash. If that fails, replace the sensor.

 

on some cars, a p0125 can actually be a problem with the front o2 sensor, not a coolant temp issue

 

Update. Finally got my cable in this week. For some reason it wont work with ECU flash to read the rom with Windows 8.1. Got tired of messing with it. It works fine with EvoScan 2.9. Read the Rom. Opened it up with ECU flash. Through some other threads I found info on the FAA bit for the rear 02 being enabled AND Tephra being enable for rear 02 sim. Mine wasn't set up that way. My FAA bit was turned off. Not sure why, unless it had something to do with the lower temp thermostat that was in there. I enabled the FAA bit to 1 and flashed. Drove it home last night and to work this morning. No light, and I now have movement being read on the rear 02 sensor (obviously). Now my question is, will this have any adverse effect on my performance i.e. timing and such, now that the ECU has access to the rear 02 info? Or will the Tephra sim still provide this? Seems to be running just fine, I'm just wondering. Thanks guys for all of your help.

 

You've done it correctly. The FAA bit for rear O2 sensor should be "1" - enabled. It seems that was your issue.