1995 Chrysler Concorde now in limp mode

Hi johnlog. Welcome to the forum. I could be wrong for the second time this year, but I don't think you're good enough to take out a computer. :) Instead, look first for blown fuses. There are two different computers. The Powertrain Control Module (PCM) is for the engine and radiator fan. The Electronic Automatic Transmission Controller (EATX) is for the transmission. When the transmission isn't working, it should be stuck in second gear as evidenced by the low power when starting to move. Second gear is the spring-loaded default that allows the car to be driven slowly to a repair shop.

Getting back to the fan, it should turn on with the engine running when you unplug the two-wire coolant temperature sensor. If it does, the system is working. When the fan doesn't run, the most common cause is a defective fan motor. The next most likely cause is a blown fuse, ... Due to a tight fan motor. Burned or pitted relay contacts can cause a dead fan too but that isn't real common. Some of the newer vehicles use an electronic relay module that causes a lot of trouble. Minivans started using them in '96. Not sure when the cars started using them.

Holler back if the fuses are good and we'll figure out where to go next.

Caradiodoc

You're right about the fans, but the Engine Computer does not run the transmission. That's done by the Transmission Computer, (EATX). As I recall, the Engine Computer lives behind the right head light and the Transmission Computer is on the left side.

Is it possible a connector got knocked lose on the transmission when you were working around the radiator? Nothing you could have done to the fan wiring should affect the computers. The fan motor and the Engine Computer are on the two different halves of the relay circuit.

Caradiodoc

When you said the fans run with the relay out, do you mean the terminals have a jumper wire in them? That would be necessary for the fan to run. You've already done more diagnosis than you realize. You now know the fan motor is ok, and you know the fuses and wiring are ok.

The fan circuit can be divided into four parts for testing and all of those tests can be done right at the relay socket. You've already confirmed two of those circuits are working by using the jumper wire. One terminal will have 12 volts all the time. That's the supply terminal for one of the relay contacts. We'll come back to him in a minute. A second terminal will have 12 volts when the ignition switch is turned to "run". That's the voltage supply for the coil inside the relay. It will be one of the two parallel terminals on either side of the relay. The other two circuits are the ground sides. One reads very low resistance through the fan motor to ground. That, along with the constant 12 supply are known to be working since the fan runs with a jumper wire. The last ground circuit is the other parallel terminal. It gets grounded by the Engine Computer to energize the relay's coil.

That last terminal is a little trickier to test. The easiest way is to insert a small piece of wire in the socket terminal that you can touch your voltmeter probe to, or you can try to lift the relay out enough to gain access to that terminal. With the ignition switch on, you should measure 12 volts on that terminal until it becomes grounded by the computer. That's when the relay should turn on and the fan should run.

The Engine Computer turns on either the low speed or high speed relay depending on coolant temperature and the high side pressure in the ac system when it is running. If neither circuit turns the fan on, suspect the computer. If the fan runs with the ac running, suspect the coolant temperature sensor.

Caradiodoc

Weird indeed. I'm using a '97 service manual which should be the same. They show two relays, a high speed and a low speed. I wonder if the computer is turning on one relay in response to seeing the other one missing. I do know the computer will turn the fan on when the temperature sensor is unplugged in case the engine is overheating. That's a precaution programmed in when it doesn't know the actual coolant temperature.

Caradiodoc