Expert: Roland Finston - 8/9/2011

Question
QUESTION: My 94 Chrysler Concorde is overheating...my guess is the electric fans are not come as they should.  The thermostat seems to be working..hot upper hose. I just replaced the coolant temperature sensor. Pulled the fan assembly and verified the fans worked by wiring directly to the battery. Checked resistance to all relays between pins a&c no shorts. i have heard that there is an automatic shutdown of the fan relays when coolant sensor doesnt work, since i just replaced it.. is there a reset process involved? I have the 3.5l engine fyi

ANSWER: Hi Shawn,
I know of no such autoshutdown 'feature'. So the fans never come on, even when the gauge pushes toward "H"? Have you tried for fault codes? Turn the ignition switch:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light, which remains 'on', to see it begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat the process. Then let me know the flash count numbers are, in the order of appearnce.
Have you check fuse D in the power box (20 amp) to be sure it isn't blown or have a crack in its wire?
Roland

---------- FOLLOW-UP ----------

QUESTION: Roland,
Thanks for the timely response. Assuming I read the codes right....35, 5, 12, 55 and correct the fans don't come on even when the needle is pushing H.
Regards,
shawn

Answer
Hi Shawn,
Did you see this answer to your new question?

"Did you do another code readout to find out what the '5' actually is?
I wonder about whether there might be an issue with the coolant temp sensor: have you checked the resistance reading across its terminals when the gauge is moving toward the 'H'? It should be in the range of 700-900 ohms.
Also, try jumping aa wire across pin B to pin D in each fan relay socket to be sure the fans come on.
Also check that pin A in both sockets reads 12V when the the key is in the run position.
The fan relays will close when pin 32 at the pcm is grounded (low speed) and pin 31 at the pcm (high speed) and those are connected to the C pins of the fan relay sockets.  You could pull the relays when the temp is toward "H" and see if either of the C pins show a short to ground or not.
That is a basic troubleshoot of the fan relay circuits."

So do check out the circuit. Also, if the fans are not coming on, then there should be a 'fresh code' saying what the engine controller is seeing to be the problem. But you do have to get the temp up to the point where the fans are called for, and they don't come on, for a code to be set.

Roland