P0642 and P0652 - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 10 Old 03-26-2018, 06:12 PM Thread Starter
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P0642 and P0652

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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post #2 of 10 Old 03-26-2018, 07:11 PM
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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.

2008 Unlimited Rubicon Automatic

Last edited by ronjenx; 03-26-2018 at 07:31 PM.
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post #3 of 10 Old 03-26-2018, 07:25 PM Thread Starter
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Thanks Ronjenx, this gives me a good starting point in my search.
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post #4 of 10 Old 03-26-2018, 07:34 PM
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Quote:
Originally Posted by 2500HD View Post
Thanks Ronjenx, this gives me a good starting point in my search.
I was adding a few things to my post as you were posting. Check it out.

2008 Unlimited Rubicon Automatic
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post #5 of 10 Old 03-26-2018, 08:22 PM Thread Starter
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It could definitely be a ground short. It took a hard hit.
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post #6 of 10 Old 03-27-2018, 01:10 PM Thread Starter
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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.
Thanks
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post #7 of 10 Old 03-27-2018, 05:03 PM Thread Starter
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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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post #8 of 10 Old 03-29-2018, 03:09 PM Thread Starter
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Still a dead stick. I replaced the crankshaft position sensor, no change. Still the strange cranking issue as well.
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post #9 of 10 Old 03-29-2018, 05:22 PM Thread Starter
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Cleaned all my grounds again and it fired up
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post #10 of 10 Old 03-29-2018, 05:29 PM
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Quote:
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Cleaned all my grounds again and it fired up
All is well, now?

2008 Unlimited Rubicon Automatic
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