SXGT

Have a 2004 Jeep Grand Cherokee. Is it possible that a faulty gauge cluster will kill the motor after a few seconds? Jeep starts and idles. Dash Red light says " Check Gauges" and motor dies. I've heard a faulty cluster can do this, is it true?

dave1123

It may just be the connections in the plug on the back of it. Did you look to see if any of the gauges were not reading correctly? Try removing the cluster and cleaning the connectors inside the plug and socket. The cluster is mounted by 4 Phillips screws, 2 on the top and 2 underneath the trim strip on the bottom. The trim panel is mounted on 4 spring clips and can be removed by just prying it up with a plastic putty knife or trim tool. Easy-peasy! If there is a SKIM light (a barred circle around a key symbol), that means the SKIM module isn't recognizing a valid key or is malfunctioning. This happens sometimes if there's not a clean signal in the data bus caused by bad connections. Remember the data bus is 5 volts so clean connections are vital.

Waterluvr

The data bus has absolutely nothing to do with the SKIM recognizing the Sentry key frequency, that is accomplished via the antenna ring that encircles the lock cylinder and is part of the skim module itself but that is a wireless data transfer.

The skim module does exchange data on the bus to verify the proper code written to the pcm, and it needs to recognize both the PCM code and the sentry key or it will shut the engine off after 2 seconds time.

dave1123

I agree the actual sensing is done wirelessly, but the codes are transmitted to and from the module and the PCM over the hard wired data bus! It still requires a physical connection thru plugs which can have debris in them. Any more nits you want to pick? I have found thru experience with my own vehicle that any drastic change or fluctuation in voltage in the data bus can cause the PCM to shut down. In 238k miles, I had no electrical problems at all until my dash was removed twice for a heater core replacement.

Waterluvr

Not picking, just wanted the OP to understand how it really works and your original post wasn't clear on that at all.
I'm one of the very few people you will find on DIY boards that actually owns and knows how to use OEM level tech to diagnose, program and replace these Chrysler modules and misinformation abounds here and on other forums with regard to these issues.

Sorry your large ego got bruised there sport, as you were....

dave1123

I don't have a large ego, but I AM OCD about being called wrong on something I have had experience with. I also agree it's hard to convey information to someone whose knowledge of the subject is unknown. I was blown away the day I found out that any gauge readings are NOT transmitted directly from the sensors, but are sent from the PCM after being interpreted by it.

Waterluvr

Seems you have a GIANT ego, fragile and sensitive one at that there Dave.

It's serial forum posters not unlike yourself that forget you don't own the place that always take it personally when someone else comes along and set's the record straight. You don't really understand the first thing about how the technology actually works and you certainly don't own 10K or more in tech to service and diagnose these issues with any level of proficiency. In other words, ZERO real experience with it.

This is why real techs seldom if ever bother to waste time helping people on DIY forums any more there's always one of you that just can't help themselves but get butthurt and whine. I certainly won't bother to help anyone here again on account of the likes of you.

dave1123

Wow! That's kind of severe. I'm just a mere old codger trying to make some sense of my own vehicle and how it works. Most high tech guys like you have the same problem with guys like me. Nobody will take the time to explain anything so an average person can cope with this stuff. My understanding of electronics began with vacuum tubes and large metal-cased transistors. Code is beyond my interest and I don't profess to know anything about writing it, nor could I care. This vehicle is complicated enough where I'm not buying anything newer because I won't be able to fix it. When she heads for the shredder, I'll go buy an older one.

Okay, so what do you think is wrong with this guy's jeep?

GentleBen

Dave,
I for one, very much appreciate the help that you have been giving on this forum for nearly eight years. Most do not have the expensive equipment or technical expertise to diagnose the many mechanical and electrical problems that we encounter. I have not seen where you claim to know it all, but you do take the time and effort to share your hard earned knowledge. For that I say "thank you, sir"!

SXGT

OK guys. back my issue. I need to test the volts then. Also the cluster lights do come on so it should be getting the 5 volts? I will test to make sure. I did see the SKIM light but didnt pay attention to if it turned off or not before the engine shut off. Engine is like you said, turning off after 2 seconds ~ What is it about the cluster that could cause my issue? I have a second cluster but have the same issue, making me think its NOT the cluster or the 2nd cluster also has the same problem.

So if it is a SKIM issue...do I address the key 1st or ... the PCM. what is the next step

dave1123

The point is I don't know. I'm assuming you may have a loose connection in the electrical feed somewhere. Try this, turn the key on and wait until the warning lights light up. All the gauges should become active. After the lights cycle off, try starting it. It should start, then shut off as you say. See what the gauges say then. Pay attention to the SKIM light to see if it stays on after it dies. Normally the warning lights will go out as the systems come on line after it starts. With mine, the ABS, airbag, and SKIM lights wink out as it begins to run for a few seconds.

Just for jollies, pull the tilt lever and drop the steering wheel to it's lowest setting, then try starting it. I've heard the column wires can break causing the SKIM to not send the code. In extreme cases the ignition key won't start the truck because of this.

SXGT

OK put the OBD2 upto it and got code P1686 No SKIM bus message received. and yeah that light with the key comes on. Dad told me it had this issue previously and the mechanic re did the wires and it worked for a few month and they told him it may go bad again.

Should I start with the Key or the Immobilizer Module



EDIT: found some more info. People buying a new ECU/PCM and taking the SKIM Off the steering column. Do I need a specific PCM with no SKIM to make this work with my SKIM module removed or does the PCM learn from the old SKIM and by not having it connected it just wont bother with it?

01SilverWJ

OK. For the record, here is how it works. When you turn the key to "run", the SKIM reads the chip embedded in the key wirelessly. If it matches one of the keys stored in SKIM memory then it transmits an "OK" message over the bus to the PCM based on the VIN that is stored in the SKIM memory. If the VIN in the SKIM and the VIN programmed to the PCM does not match, the PCM does not let the vehicle continue to run, or obviously if it matches everything works fine. Obviously if the key doesn't match one of the ones in SKIM memory then that "OK" message doesn't get sent, I (think?) that a "NOT OK" message gets sent?. You can see this without even starting the vehicle. Turn the key to run, and if everything is functioning properly then the SKIM light will turn on and then turn off after a second or two. If there is a VIN mismatch then the light will turn back on in less than a second and stay on. If the key is not found in the SKIM memory then the behavior is similar but I have not seen it recently so I don't want to describe it without being 100% accurate. The cluster turns the SKIM light on or off based on messages on the data bus. The SKIM sends these messages and I'm fairly sure that the PCM does too in the case of a VIN mismatch. And you can program the SKIM to use any key that physically matches the lock cylinder with a decent shop level scan tool. To do that you need the SKIM PIN unless the tool will read it (some aftermarket tools do, as far as I understand, the dealer tools don't, but the dealer has access to the PIN through TechAuthority) The PIN came in the original paperwork with the vehicle, and depending on the dealer, they may provide the PIN to you if you can show proof of ownership, sometimes for a small fee. Of course they can program or clear keys into the SKIM also.

For reference, here is what a bus is: https://en.wikipedia.org/wiki/Bus_(computing)

With that said, the entire bus has to be in good shape without opens or shorts. The problem is that it runs through the entire vehicle, between all of the different control modules. There are lots of them - http://www.wjjeeps.com/modules.htm. If there is a problem with the bus anywhere in the vehicle then it can prevent the SKIM from sending its message successfully to the PCM, and you will see exactly the symptoms that you're seeing. The gauge also gets all of its information over the bus so it's a crapshoot what you see on there if anything at all.

First place to start - believe it or not, the driver's door, especially where the wiring runs between the door and the body. I'll tell you what my experience was and that it was very similar to what I've heard from other forum members on JeepForum. I had the behavior you're describing one morning but noticed that when I turned the key to "run" I heard electronic noise out of the driver door speaker. Some of the gauges did a kind of "twitching" and a lot of the warning lights were on. Thinking the door was the place to start I pulled the connector loose at the a-pillar on the body and some rusty water ran out. Water had gotten into the connector somehow and caused enough corrosion that it had started to conduct electricity. The bus goes out to the door because the driver door module (DDM) is there. The water was conducting electricity away from the bus wire to ground, the speaker wires, and everything else enough that it wasn't allowing clean communication elsewhere on the bus. Some cleanup and WD-40 to drive the water out, plugged back in, and I was on my way. But I understand more commonly that the wiring itself in that area just breaks eventually (and then maybe shorts?) because of the open/close cycling on the wire.

At the very least, carefully unplug the driver's door and see if your WJ will start. If it does then you've narrowed down where the problem is.

If the vehicle wouldn't start I would be inclined to blame crank or cam sensor, or PCM. The PCM is the bus master, and if it's malfunctioning like more and more of them are doing, then the motor wouldn't start either. I don't think that's your case here.

Now you have me wondering exactly what happens when there is no matching key in memory, I need to clear them out of my SKIM and try it, but that's irrelevant to your problem here...

dave1123

You know, that's a good point I hadn't thought about, I mean the driver's door module! I know it's more than a bunch of switches, but I forgot it's part of the bus system. And for future reference, the keyless entry receiver is in the passenger's door attached to that switch bundle. I just had to fix broken wires in 3 of my doors!

SXGT

OK so the wires going to cluster are getting good volts when I tested them

All wires and connections in D door and steering column looks perfect. Did not have a chance to get to P Door but the fob is locking and unlocking the doors.