1997 850: P0117 (ECT Circuit Low Input), NEED HELP W/THIS 1

dville_gt · Post by **dville_gt** » 22 Mar 2009, 20:55

Okay, over the past two weeks I have done a lot of work to my 1997 850 (timing belt, waterpump, tensior/idler, pcv system, radiator, hoses, etc.)

Now, I have had this problem where my temp gauge just doesnt work randomly, some times it wont work at all, sometimes it will come on mid-trip, sometimes it'll be on all the time. This problem has never caused a check engine light or anything, but since I was already doing all this work I figured I'd throw in a new ECT sensor and see how that works. After driving a little ways I got a P0117 code and now every time I start the car the fans automatically come on and stay on. I figure it might be a bad sensor, but that still doesnt answer why I randomly get readings to the dash with this sensor just like the last one (today when the motor was dead cold the temp gauge went right to the middle where it is supposed to be, yet the engine was dead cold).

So, if I throw in a new ECT sensor (hoping this fixes the code), how do I go about getting the temp gauge to work again? One night out of desperation I hit my dash board and low and behold, the temp gauge sprung to life. I have no idea whats wrong here. HELP!!!!

Post by **Matty Moo** » 22 Mar 2009, 21:32

This is how it works.

If you unplug your ect sensor, your fan automatically comes on, as there is no resistance recorded from the ect. The ect works by resistance, which is ohms. As the temp changes, the ecu reads the changes in resistance from the ect. The ect talks to the ecu, then the ecu does what it does, which is turn on fans, talk to the temp gauge and other stuff that makes the car run.

So, this would tell me that either you have a bad ect, or a bad connection between the ect and ecu. The temp gauge gets its reading from the measured resistance recorded from the ect. I've never heard of a temp gauge going bad.

As far as punching the dashboard and the temp gauge suddenly working, there's a bad connection in there somewhere. Which is odd, as most of your electrical problems aren't usually in the dashboard.

If the ecu you put in isn't new, put a new one in.