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Discussion Starter #1
First a little back history. I got an 08 jk wrangler x that had been rolled. I put a new tub on it and a front axle. Today i got to the point i could try to start it but before trying it i ran a scan and got codes P0642 and P0652. Sensor Reference Voltage 1 and 2 Circuit Low. When i tried to start it it would crank intermittently and not start. Can some one give me an idea as to where to start or at least a pin code at the pcm? Also which sensors are 5v?
Thanks
Jeff
 

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P0642 indicates the voltage in the Primary 5 volt supply circuit is low. (PCM connector C2, pin 29)
The Primary 5 volt circuit feeds the sensors for the accelerator pedal position circuit #1, crankshaft position, and the throttle body.

P0652 indicates the voltage in the Auxiliary 5 volt supply circuit is low. (PCM connector C1, pin 27)
The Auxiliary 5 volt supply circuit feeds sensors for the accelerator pedal position circuit #2, EGR valve position, transmission variable line pressure, camshaft position, and manifold absolute pressure.

A short to ground or a bad sensor in those circuits can cause these codes.
A problem with the PCM can cause the codes, too.
 

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Discussion Starter #6
It appears that i don't have any power to c1 pin 27 or c2 pin 29. Any ideas? If i had the starting point i could run a continuity test on these 2 wires. I really don't want to undress the hole loom looking for it.
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Update, i was mistaken. i have power to the ecm and power out of pin 27 &29. Guess i need to check all sensors. One strange thing it is doing is when you crank the engine it cranks very sporadically. When you turn the key it will crank for a couple of seconds then pause then crank and then pause. It hasn't even tried to start yet. not even a sputter.
 

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Discussion Starter #8
Still a dead stick. I replaced the crankshaft position sensor, no change. Still the strange cranking issue as well.
 
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