What should the voltage going into the coolat temp sensor be? My jeep has been running poorly and I figured it was the temp sensor and this was confirmed with a code 22. I replaced the temp sensor and now it is still doing the same thing. The resistance at the ECU pins 2 and 4 is right and the wire is getting a good connection. The voltage going into the sensor bounces around 2 volts and then other times it drops down 1.4 volts or so. What should it be and what could cause the fluctuations?

Why don't you reset the ECU to the factory presets and then see what it does. Just remove your + battery cable(s), ground them out after removal for ~30 seconds. Then re-attach the cable(s), start the car up and take it for a ride making sure you don't sitat idle too long during this initial startup. You are now running on the factory presets for the ECU. Make sure your ride is at least 30 minutes or so to get the engine up to normal operating temperature (closed loop mode). Drive it in traffic, get up to highway speeds, park it, back it up, etc. Your jeep actually "remembers" all of the inputs it receives during the first 50(?) start up cycles. Your may have some old values in it and that could cause your heep to get "confused". And it cost nothing to try this.

 

Yeah, I tried this already. The code will be gone initially and then come back after a drive. I'm pretty sure something on the cirtuit going in to the sensor is fried or lose causing the fluctation in voltage. I would think this would be a 5 volt circuit anyway. I just need some confirmation of what it should be.

 

What should the voltage going into the coolat temp sensor be? My jeep has been running poorly and I figured it was the temp sensor and this was confirmed with a code 22. I replaced the temp sensor and now it is still doing the same thing. The resistance at the ECU pins 2 and 4 is right and the wire is getting a good connection. The voltage going into the sensor bounces around 2 volts and then other times it drops down 1.4 volts or so. What should it be and what could cause the fluctuations?

it should range between 1 and 4 volts for the most part. it changes with the temp obviously. sounds like you're in the right range. could be in the connections somewhere.

 

voltage going in to the sensor will be a 5volt reference from the ecm. then the temp sensor varies resistance to change the voltage going back to the ecm. if you don't have the 5v at the sensor, you have excessive resistance in one of the wires going to the sensor. also check all your engine grounds, they tend to rust the quickest, and cause all kinds of whacky problems.

 

Thanks jipjip, that was the reply I was looking for. I was trying to confirm I should be seeing 5 at the sensor so now I have a place to start looking for problems. I assume if I'm not seeing 5 at the ecu then the ecu is bad or there is a bad ground. What do you think?

 

start by doing pin checks at the ecu. i'm not sure which pins are for that circuit, but a wiring diagram will help. if you have 5v coming out of the ecu, the problem is somewhere between the ecu and the sensor, if you don't have 5v from the ecu, then a ground could be the culprit, or the ecu is bad. good luck:wave:

 

With the temp sensor plugged in and the engine cold I get around 3V going into the sensor. If I unplug the sensor it bounces around closer to 5V. I pulled the ecu and it is making a high pitched whine (in excess of 15KHz...about like a mosquito). The jelly is cracked and I imagine water could have gotten in but I don't know if this is even an irregularity. One component seems pretty hot. Should I try replacing the caps? Does anyone have the link to the page with the howto?