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Old 04-12-2015, 05:59 PM
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New member need help.

My 04 WJ 4.7 liter has key light on, jeep will not start even for 2 seconds. Cranks just fine but will not start. I disconected the batt for a min. The it started fine for 2 or 3 starts then goes back to not starting. Did the battery trick and the jeep started did this 2 or three more time but now even the battery trick does not work
Key light is on but it is not blinking put the OBDii reader on it but get only error. Tried the key on off three times get nothing not even done.
Replaced the crank sensor with real jeep sensor. Battery is new. No mods
I am thinking PCM any other ideas?

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Old 04-12-2015, 06:06 PM
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Re: New member need help.

Issues with the vehicle anti-theft system can cause this.
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Old 04-12-2015, 06:48 PM
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Re: New member need help.

Welcome to the garage.
That the key dance doesn´t work and a scanner gives an error, means that the PCI data bus has a problem or the PCM is locked out. There are many components on this bus, which can kill the bus when they have a problem. On older WJ´s, there was a PCI bus diagnostic plug with a shorting cap. Removing this cap would remove most of the components from the bus, except the PCM, TCM, SKIM and a few more. Unfortunately jeep decided to remove this plug. Now you will have to remove each component (maybe that pulling the fuse is enough, but not sure) and see when the bus power returns to normal. It seems that normall bus power is 2-2.5 V (the bus voltage is in fact not a steady voltage, but a square wave, but the nominal voltage should be 2-2.5V. You can measure this at point 2 from the OBDII port. The PCM is the most important module for the PCI data bus, but any of the other modules can bring it down.Also moisture in connector C200 in the passengers footwell area is known to short out the bus. But since a battery reset will solve the problem for a few starts, it seems to be more a module which freezes up and shorts out the bus. I would start by removing the fuses from the BCM and see what happens.
Here follows a list of the components connected to the bus: PCM, TCM, BCM, SKIM, ABS controller, driver door module, passenger door module, AC head unit, EVIC, radio. (maybe even a few more, but this is what i remembered now)
But after all this being said, without the communication between the PCM and SKIM via the PCI bus, the engine should still start, but shut off after 3 seconds. If it doesn´t start at all, most probably the PCM is faulty.
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Old 04-13-2015, 10:34 PM
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Re: New member need help.

Thinking further about it, did you check the fuses for the PCM? Fuse 19 in the PDC and fuse 12 on the junction block. Do you hear the fuel pump running for 3 seconds when ignition is switched to run?
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