Temperature sensor problem?


Asked by Sep 06, 2013 at 09:14 AM about the Chrysler 300M

Question type: Maintenance & Repair

My 2003 Chrysler 300m overheats - it seems to be only when I am stopped or in stop and go traffic.  I've just recently replaced EVERYTHING in the cooling system; thermostat, water pump, radiator, hoses.  It ended up needing the head gaskets replaced.  Now a month later, it's overheating again, but only in stop and go situations.  The fans are working, but I don't believe they ever kick into high speed.  I checked the relays - there are two.  One is labeled 'radiator fan Hi/Low'.  I assume this one has to be working for the fans to work at all, so I think this one is ok.  The other one is labeled 'radiator fan Hi'.  I'm guessing this is the one that allows the fans to kick into high.  To check it, I switched places with the Hi/Low relay, and the fans still work at low speed.  Can I conclude that this means the Hi speed relay is ok?  If so, would that mean that the temperature sensor isn't working, that it is not sending a signal to the relay to kick on the fans at high speed?
My plan is to replace the coolant tneperature sensor.  Please let me know if I'm barking up the wrong tree.  Thanks.

13 Answers

Does the fan still stay on 'low' with A/C on?

3 out of 3 people think this is helpful.

Yes, I believe it does.

Sorry, I had to go unexpectedly. A new temperature sensor will sure not hurt, and maybe, just maybe solve it. But the fact that the relay worked on 'low' is not conclusive proof it is good, it may be working on low only. On this image I found for the 300m there is a third relay, the red box lower than the other two. Did you check that? click image to see it

6 out of 6 people think this is helpful.

And check this out: http://www.youtube.com/watch?v=AdIYm9kM5E0

5 out of 5 people think this is helpful.

I don't think this diagram doesn't matches the layout of my car. Anyway, I looked at all the other relays and fuses and didn't see a third one that seemed to have anything to do with the radiator fans. Just to be sure - is ther only one coolant temperature sensor? Is it the same sensor that affects the dash guage? The guage seems to be working ok-

That I will have to check. And the image is labeled 2003 ..300m But that would not be the first time they are captioned wrong, sorry 'bout that

1 out of 1 people think this is helpful.

I could find only one sending unit in parts suppliers. So it appears to work both, gauge and fan. Here is a schematic for what it's worth...sorry I'm not being any help. This is turning out to be more difficult than I thought

3 out of 3 people think this is helpful.
Best Answer

OK..wait, that shows a high speed motor and a low speed motor, we may be getting somewhere after all. Maybe run a hot wire to each motor and see if they both work... It even indicates color of wires

1 out of 1 people think this is helpful.

Ok - this isn't making sense to me. My understanding is that there are two fan motors (2 fans = 2 fan motors) but I thought that they both ran at low or high speed depending on the need at the time. It doesn't make sense to me that there is a low speed motor and a high speed motor on the same fan - how does that work?

1 out of 1 people think this is helpful.

I'm really not sure how it works, but if you click on that schematic it will get almost full screen, and I can see 'high speed fan motor' low speed' fan motor, on the lower right in the box "fan motor assembly" do you see it that way? The bottom image?

2 out of 2 people think this is helpful.

Yes, I see that - but does the 'Radiator Fan Motor Assembly' box represent one of the two fans (each having two motors) or does it represent the entire two-fan assembly? If so, that indicates that only one of the two fans is supposed to run at high speed. Is that correct?

1 out of 1 people think this is helpful.

It is the entire two~fan assembly, everything there is, and correct, one fan runs faster than the other. I don't know what they designers were thinking. This is new to me, a learning experience..I have been looking at owners forums and nothing..nada. I have an idea that it has something to do with the A/C and intend to do further reading.

2 out of 2 people think this is helpful.

I appreciate your help but don't spend too much time on it unless it just really interests you. Personally, I'm not that interested in cars until mine isn't working properly. I'll probably stop to buy a relay and temp sensor on the way home and see if either of those will fix it. Then, hopefully have a good weekend after that! Again, thanks for your help and have a great weekend!

1 out of 1 people think this is helpful.

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