Expert: Roland Finston - 6/27/2011

Question
QUESTION: I have a 1999 Chrysler 300m, I just replaced the fan assembly as both motors were bad but the fans still do not turn on and my car is overheating at idle.  Any suggestions on what to check?

ANSWER: Hi Cary,
The radiator fans require 3 specific fuses to be good: under the hood fuse B (30A) and fuse E (40A) and in the box behind the left end-cap of the dash you need fuse 21 (10A). So verify those are all patent. The low and high speed fan relays are activated by the powertrain control module which will activate the fans based upon the temp sensor for the coolant and also whether the AC is requested or not. You could verify whether you see any voltage on pins 3 or 4 of the new fan plug (tan or light green wire, respectively) when the temp is getting well above 1/2 gauge.  If not and the fuses are OK, then either both relays have failed or the temp sensor is inaccurate.
Have you tried for fault codes using the ignition key:"on-off-on-off-on and leave on", doing that in  5 seconds or less elapsed time. Then watch the odometer window to see if the mileage reading changes to show some 4-digit numbers preceded by P which would be clues as to the problem. Let me know what you learn.
Roland
PS Please 'rate' my answer and consider giving a "yes" response to the question about a nomination for me to be 'volunteer of the month'. Thank you

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

QUESTION: I now have a code says I need a auto trans speed sensor how do I replace this?

Answer
Hi Cary,
There are two speed sensors: if the codes were 0715 and 0720 those would be the input and output speed sensors, respectively. So check out whether and which sensor is indeed the case or not. If one is, then you will find the two sensors on the side of the transmission that faces the driver's side of the car about midway between the upper and lower surface, and the input is near to the bellhousing of the trans while the output is toward the rear of the trans. Each has its own plug (lift tab to release) but the wires come out of a common harness in between them. The sensors are not identical so don't mix them up. They unscrew after you remove the plug. Be sure to reuse the weather seal which may come off with the sensor or stay at the socket. Screw the new ones in about as tight as a spark plug, 25 foot-pounds. Shop around for the best price on these as they are in the range of $50-100 each depending upon where you buy them.
If the codes were not the ones I listed, then tell me what are the numbers of the codes.
Roland
PS Thanks for the prior rating/nomination. If you would care to do that again I would be very pleased.