Hello, I have been chasing a nightmare of an issue with my Jimmy. One day it just stopped running and I ended up replacing the entire ignition system before it would run again, but only if you floor it when you turn the key. After all of this the temp gauge wasn't working and I was getting a temp sensor/closed fuel loop code. I have replaced the sensor 4 times and have replaced the pigtail. I have 5v with no sensor plugged in, and 2.2-2.4v with a sensor plugged in. With my scanner on live data stream it reads 50-52 degrees all of the time no matter what. I am assuming it is electrical somewhere. The gauge does go up with a jumper wire. What could be my problem here?

 

What codes are you getting. Is the coolant system full and properly bled to remove air?

George

 

Also, with the sensor plugged in, what are the voltage readings for a few different engine temp conditions like cold and fully warmed up?

George

 

Code is P0125-00, coolant is full with no air in the system. As of right now it is reading 86 degrees on a fully warmed up engine at 1.76 volts. Thats about 10 degrees higher than ambient right now.

 

So your getting voltage change but its limited to 2.2V cold to 1.8V on a warm engine?

George

 

Yes, it seems that no matter what it is only reading around ambient temp no matter how warm the engine is.

 

OK now I am confused. I get it that your gauge reading is wrong but to help us find the root cause I am trying to figure out the range of voltages that you are measuring at the hooked up sensor between a cold and warmed up engine.

George

 

All voltages I have read have been between 2.x and 1.7 so far. No numbers I have given have been from the gauge, they are from live data stream of my Matco MaxLite. Voltages have been verified with a power probe. The voltage does not change with a cold or warmed up engine, but is different from day to day and seems to correlate with the ambient temp.

 

I am looking for voltages at the temp sensor connector while plugged in to the harness, not voltages at the gauge or the voltages displayed on the scanner.

1. So with that in mind, those voltages do not change with temperature of the vehicle coolant on any given day, correct?
2. Unplug the sensor and measure the voltage from hi ref (yellow) to frame ground and hi ref to lo ref (black) with a voltmeter.
3. Unplug the sensor and measure its resistance in ohms across the two terminals on a cold engine and again on a warm engine.

George

 

Thank you for the help so far and I am not trying to be difficult, voltages measured at the sensor connector with the sensor plugged in range from 1.8v to 2.0v. That can vary throughout a single day. For what you stated in step 2 I get 5v and 5v. These do not change with engine temp. I would have to get back with you on Sensor ohms, but I find it unlikely I have gotten 3 bad sensors in a row.