Coolent sensor issues

[evilspot]

Need some help, the temp gauge has stopped working, and the Service engine light is on and coolent fan comes, on shortly after car is started (under 30 sec.). Here are some part. 2001 3.8L, little over 103K. I have already replaced the coolent temp sensor (just below the air intake) Seemed to work for a short time (15 min) then stopped :( . The code that is causing the SEL states that the temp sensor is not working, and I guess that since the sensor output is not working, it is keeping the fan on. Here is what I think in happening. I think there is an open between the sensor and i guess the MB (not sure where it go to first). Is there an easy why to check if the sensor is still good (I assume that it is just a resistive load based on temp). If the temp sensor is good, where does it go back to and how can I check that path. This is not an issue now, as it is winter and I have no leaks, but I worry about summer and if I get a leak in the system, as I can not verify temp. I am not so much looking to simply add an after market sensor as I would like fan not to run all the time but only when needed. Thanks

[Christopherrr]

Re: Coolent sensor issues

A broken connection would trigger the code and run the fans. I worked on my TB and forgot to reconnect the wires from the fans to the sensor...once I plugged it back, code went away and fans stopped.

Check your wires and connections, make sure it's clean and the straight.

Though, I didn't get an SES light...just heard the fans run and put my scanner on it and found out the problem.

[evilspot]

Re: Coolent sensor issues

Christopherrr, thanks for the reply. I have already check the wire at the coolent sensor, looks good and appear to be making good contact, do not appear to be broke at the sensor. Do you happen to know were the other end terminates at? (so I can check the path, could have an open somewhere esle that I can not see.) Thanks

[Christopherrr]

Re: Coolent sensor issues

A clogged sensor would also trigger a SES.

If you are using Dexcool take off your radiator cap and see if it has the gunk that Dexcool is prone to create...it's gooey and looks like poop. If you have this build up it can accumulate on the sensor causing it to fail or appear to be nonfunctional.

I would just see if it's clogged.

[evilspot]

Re: Coolent sensor issues

you know I had a system flush done the same time I had the sensor replaced. Bought the sensor was going to replace myself looked at my radiator, looked real bad, had a shop do a system flush and a presure test, they offered to slap the sensor in, like I said it worked to ~15min then failed, it is possible that some of it did not get flushed out and is not stuck to the sensor, I will try to check this, this weekend. Thanks

[jackiegeorge]

Re: Coolent sensor issues

it,s very possible you have a bad new coolant sensor. check the resistance from the new one to the old one. your ecm could have issues also. steve

[evilspot]

Re: Coolent sensor issues

Sorry it has taken me so long to reply, but it has been a bad week. I have checked the sensors and it seems to be correct. However the larger issue is that while driving my temp gauge will start to work and then start to fail agian (when the temp sensor start working the fan will turn off). based on this I have to go back to one of my original assumption that there is a open (broken wire) in the path, does anybody know were this sensors wire trace back to and how to get to them so that I can verify/role-out the broke wire theory. Thanks

[Kevin01]

Re: Coolent sensor issues

I had similar issue but mine did not show any temp any time. I had to reset the PCM. Have you checked the voltage going to the sensor? One should read about 5 volts other should be in the millivolts range. Is easy way to test it out. It should lead to the PCM which is on the passenger side of the engine bay near the window.

[evilspot]

Re: Coolent sensor issues

Kevin, thanks for the information. I took a look at things this weekend and I am getting 5V on one and the other has a low impedance short to ground. Going back to my original thought, the sensor is just a temp dependent resistor. With it plug in it just completes a simple voltage divider, as the temp changes the voltage value changes, and this is used to determine the coolent temp. what I determined this weekend is that my old sensor has a resistance of ~3.5K and still does very based on temp, I was able to determine that I did have 5V and that when I plugged the temp sensor in nothing changed with the car. I am going to go by RS and get some resistors to try and very the voltage as seen by the PCM to see if that makes a difference. What I am worried about is that the wires are not open (as I originally thought), which means that it seems like the PCM is ignoring the input data. I am open to any suggestion that anybody might have as to fix this issue. I do not belive that the temp sensor is broke and I have the correct voltage that the pins. any thoughts Thanks

[Kevin01]

Re: Coolent sensor issues

Here is some info about coolant sensors on 4th gen, pics are froma 1995 probably V8 but, might help out a bit. http://shbox.com/1/4th_gen_tech2.html#ect

Have you reset the PCM, that was only problem with mine. Was really strange all of a sudden one day did not report any temp.

[evilspot]

Re: Coolent sensor issues

Kevin, intresting link with a good table in it. First how do you reset the PCM, I do not know how to do this and do I need anything special to do it. Second I would like to thank everybody that tried to help. Here is the current status, since time is something I no longer have a lot of, I now take my car to have the oil changed (I know shame on me), once I had the oil changed on monday evening (was not low, or overly dirty, just normal) the temp sensor has started working again and all thing appear to be good. This does scare me a bit though, I hate it when things just start working again. This means that there is usually a larger hidden problem that I will have to deal with in a little while. Thanks. Aric

[Kevin01]

Re: Coolent sensor issues

Easiest is probably unplug the baterry cable for 10-15 min. I did not want to reset my car stereo, so I turned the ignitiion to On (do not start engine). Unplugged both PCM fuses they are under the hood on the driver side. Wait 10 min turn iginitioun off put fuses back in. Go back and start the car see of SES light goes away etc..