moteman

Jeep Grand Cherokee Laredo, 4WD w/4.0L and Automatic transmission.

Shut it off and now all it will do is turn over.

Battery is good!
I do have spark at the plugs!

The relay for the fuel pump doesn't click when switched on.
The fuel gauge or volt meter do not react when switched on.
The check engine light does not immediately come on when switched on but will come on and stay on after a couple of attempts to start.
The security light for the immobilizer comes on then goes out and comes back on and stays on until the key is switched back off.
The snap on scan tool does not communicate with any of the modules.

If anyone has experienced these symptoms and may be able to help, I will take all the advice I can get.
I am leaning toward a bad PCM myself but I want to be sure.
If it is the PCM, can one be obtained aftermarket and installed without having to go to a dealer?

GarrettJ

You take your batter in to have to tested?

Are you getting voltage to relay? If so try switching it out with another one that's not on starting circuit

moteman

I've tested the battery, it is good. There is voltage to the relay and the relay has been tested and is good. Im just not getting the signal from the PCM to the relay when the key is switched on.

I have several years experience as a service tech for GM. So I am pretty sure I have covered all the basics. I do not, however, have a whole lot of experience with jeeps or any other Chrysler products.

moteman

Alright, I run across someone else who described having the exact same symptoms as I was having, including the fuel gauge issue, and the no communication with any modules issue, and he was also not able to pull any codes. He had taken his Grand Cherokee to the dealer who, after attempting diagnostics, told him the PCM was bad and that it would have to be replaced. After spending the big bucks on the PCM and the problem was not fixed, they then told him that he needed to replace the crankshaft position sensor. The crankshaft position sensor fixed his problem.

Just because I was at my wits end, I went and purchased a crankshaft position sensor for mine and to my amazement, it repaired my problem. I knew that the sensor would keep the vehicle from starting, but I never would have imagined that it would cause all the other issues, including the lack of communication with the PCM.

If anyone exhibits the same issue with their Grand Cherokee, I would strongly advise replacing the crankshaft position sensor before replacing any computer modules at all. The sensor was $41.00 aftermarket and is way cheaper than a computer module.