no start, sentry key light on - JeepForum.com
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post #1 of 40 Old 04-07-2020, 06:31 PM Thread Starter
kodiac12
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no start, sentry key light on

So my wj cranks hard, but will not start. Sentry key light is on none of the gauges work, gas and cel light come on after a few seconds and beep each time. I've been going through all my wiring and grounds, so far so good. Replaced all fuses, swapped relays around. Automated Driver door lock has not functioned for some time after an alarm install(has since been removed). Battery is charged to 12.35 volts and have tried to start while hooked up to charger. Cleaned pcm connections, tested the obdII port. I need more ideas and what to look for. How do test the pcm? Everything works too, lights, radio, fans sunroof etc.. got a random misfire code week before it started had it started and drove 20 plus miles a couple times and now it won't unlock. Thanks for any help will be watching and updating.

I had got two codes pulled and rest everything.
Stack iver flow failure
Rolling code failure

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post #2 of 40 Old 04-07-2020, 06:41 PM Thread Starter
kodiac12
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since i cant seem to edit my post, i have a 2002 with a 4.7ho overland edition.
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post #3 of 40 Old 04-07-2020, 06:57 PM
JGCJeep
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With key on engine off, do you hear the fuel pump prime?
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post #4 of 40 Old 04-07-2020, 08:37 PM Thread Starter
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no but there is fuel pressure
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post #5 of 40 Old 04-08-2020, 12:46 AM
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Now i dont have any personal experience here, but doesn't that sentry light spell trouble for the SKIM module? I was under the impression that if that light was on, that the SKIM was overriding the key.....(like you are trying to start the Jeep with the wrong key). I wonder if that also will disable the gauges as well? Just brainstorming here,,,,

'00LMTD-4.7l,242hd,D30,D44A,3.73's,True-trac front,Spartan rear,4" short arm lift,JK'sW/32's
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post #6 of 40 Old 04-08-2020, 05:28 PM
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Originally Posted by Bigrigr View Post
Now i dont have any personal experience here, but doesn't that sentry light spell trouble for the SKIM module? I was under the impression that if that light was on, that the SKIM was overriding the key.....(like you are trying to start the Jeep with the wrong key). I wonder if that also will disable the gauges as well? Just brainstorming here,,,,
The problem here is likely a failed pcm that won't respond to the skim module when it calls for the security code, or the pci bus that allows data to transfer between the pcm and skim modules has failed also causing the issue with data from the pcm to the dash.

Continuity checks of the pci bus will confirm or rule out the latter of the two.
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post #7 of 40 Old 04-08-2020, 08:42 PM
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Originally Posted by Waterluvr View Post
The problem here is likely a failed pcm that won't respond to the skim module when it calls for the security code, or the pci bus that allows data to transfer between the pcm and skim modules has failed also causing the issue with data from the pcm to the dash.

Continuity checks of the pci bus will confirm or rule out the latter of the two.

Ah Hah! I knew it had to do with that damn SKIM module somehow!
But seriously, I hope this can be narrowed down easily, because this kind of repair can get sketchy. When you say "Continuity checks of the PCI bus will rule out the latter of the two" You might as well have called me names in Italian.... I will be watching to see how this one turns out...

'00LMTD-4.7l,242hd,D30,D44A,3.73's,True-trac front,Spartan rear,4" short arm lift,JK'sW/32's
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post #8 of 40 Old 04-08-2020, 09:55 PM Thread Starter
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[/QUOTE]When you say "Continuity checks of the PCI bus will rule out the latter of the two" You might as well have called me names in Italian.... [IMG class=inlineimg]/forum/images/JeepForum_2016/smilies/tango_face_smile_big.png[/IMG]I will be watching to see how this one turns out...[/QUOTE] haha me too
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post #9 of 40 Old 04-08-2020, 09:57 PM Thread Starter
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Thanks for the input, I get a feeling it's pcm as well.. will keep you guys updated, will be testing more electrical this weekend
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post #10 of 40 Old 04-09-2020, 06:28 AM
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When you say "Continuity checks of the PCI bus will rule out the latter of the two" You might as well have called me names in Italian.... [IMG class=inlineimg]/forum/images/JeepForum_2016/smilies/tango_face_smile_big.png[/IMG]I will be watching to see how this one turns out...[/QUOTE] haha me too[/QUOTE]

Continuity check = verifying point of origin to point of destination in a circuit using a digital test meter set to the ohms index and probing both ends of the circuit with the test leads.

This will show you two things, an open or closed circuit and the amount of resistance (ohms) over the length of a closed circuit. You can also test that same circuit for continuity to ground that will show you a short causing malfunctions.

In more practical terms for your Jeep issue in the wiring harness there is a main pci bus circuit that carries data from the pcm module that branches off to various other locations like the skim or body modules. We want to unplug the pcm connector and identify the socket location at that point as a main reference test point in addition to unplugging the connector on the skim module and identifying the pci bus location on that connector as the alternate test point.

We want to see continuity with little to no resistance between the two ends of those connectors, that shows us the circuit is intact so data can transfer between the modules.

If you want help to trouble shoot that send me a PM with your VIN number and email, I do all the pcm and electrical trouble shooting help for members here that way as it's usually 30-100 back and forth exchanges in a typical scenario with folks new to using a test meter.

If your pcm is suspect I can program a replacement for you that's plug and play ready to get you back on the road if needed, majority of the time with a crank no start and dash issues like you have the pcm is bad.

If you happen to be local to me I do have free loaner pcm's available to forum member to use for most of the Jeep models that speeds up the troubleshooting process your welcome to try one.
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post #11 of 40 Old 04-09-2020, 07:07 AM
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So, Im not trying to muddy the waters here, but just trying to understand. I get the whole resistance check of a circuit, but what is news to me is this BUS itself. Are you saying that the bus is just a standard electrical circuit(regular wiring and connectors,etc) that just has a bunch of splices in it to feed multiple devices? So we can identify this circuit by color coded wires at each end(just like any other circuit) and conduct our continuity and resistance just like any other circuit? Do the other modules hooked into the circuit have to be isolated while doing this? Such as disconnecting the Trans module while testing the circuit to the PCM for example?

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post #12 of 40 Old 04-09-2020, 10:02 AM
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Quote:
Originally Posted by Bigrigr View Post
So, Im not trying to muddy the waters here, but just trying to understand. I get the whole resistance check of a circuit, but what is news to me is this BUS itself. Are you saying that the bus is just a standard electrical circuit(regular wiring and connectors,etc) that just has a bunch of splices in it to feed multiple devices? So we can identify this circuit by color coded wires at each end(just like any other circuit) and conduct our continuity and resistance just like any other circuit? Do the other modules hooked into the circuit have to be isolated while doing this? Such as disconnecting the Trans module while testing the circuit to the PCM for example?
The Bus lines meet at a connector under the steering wheel. If you disconnect the cover it separates it to some various modules.
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post #13 of 40 Old 04-09-2020, 03:25 PM
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Quote:
Originally Posted by Bigrigr View Post
So, Im not trying to muddy the waters here, but just trying to understand. I get the whole resistance check of a circuit, but what is news to me is this BUS itself. Are you saying that the bus is just a standard electrical circuit(regular wiring and connectors,etc) that just has a bunch of splices in it to feed multiple devices? So we can identify this circuit by color coded wires at each end(just like any other circuit) and conduct our continuity and resistance just like any other circuit? Do the other modules hooked into the circuit have to be isolated while doing this? Such as disconnecting the Trans module while testing the circuit to the PCM for example?
In the WJ series the main bus lies between the pcm and the TO hub (aka take off's) and this era of technology was based on a one wire protocol circuit design easily identified by wire color and location in any given connector pin or socket no isolation needed for troubleshooting in most cases unless your chasing a problem with a short to ground.

It had it's flaws with data collision issues, and aging poor quality wiring harnesses aren't helping matters at this point.

Any time you see a "My scanner won't connect at the data link but the shop down the street can do it just fine" thread is always a data collision issue. Two of the aftermarket OEM level scan tool makers included a data collision adapter device for the 16 pin connector for Chrysler products to work around the problem.
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post #14 of 40 Old 04-15-2020, 10:33 PM Thread Starter
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Thanks for the reply guys, been busy and my dad's truck got seriously vandalized the night before he was able to come help me test all the electrical.

I ended up just looking for damage and found there was about half inch of water under passenger side carpet still.. I soaked it up and tried to air dry a bit, added some moisture absorbers on Sunday. Today I went out and tried to start and had the same issue, but I decided to turn the ignition on and off maybe 6 times real fast (had a dream to try this haha)and now it's working again. Ran idle relearn and running like a charm after a month of sitting. I dont want this to happen again or next wet season, so going to continue investgating.
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post #15 of 40 Old 04-15-2020, 11:18 PM Thread Starter
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Much like I figured it's got the sentry key light on again after 2 hours of having run up to temperature and shutting down.
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