Btw it's a 2004 Jeep Grand Cherokee Laredo Sport, 4.0 Engine, Automatic

 

If you have a voltmeter, check your leads and make sure the voltage in is correct and that the issue isn't related to a wiring problem. Not that you shouldn't trust your mechanic, but when you first witness the code and test right away, then you can narrow in on the issue. Also, it may throw a code when it's not actually malfunctioning. On my 2.4l TJ I was convinced that my Cam sensor and Crank sensor was bad. But, after fixing itself, now I'm pretty sure it was an improper ground. If cleaning it solves it dielectric grease can't do any harm. Best of luck.

 

Just had the problem again today, cleaned and used dielectric grease this time.



I'm not sure what "check the leads" means, is that the part that plugs right into the camshaft position sensor? I'm about to buy this, and I'll check the leads when it arrives: https://amzn.to/2RMtnWH

were there any codes? post ALL codes

Don't remember what code says- the camshaft position sensor was bad.

Does the issue only appear when stopping- Is it stumbling as you break to stop?

I'm going to buy this so I can read the codes, I'll post them once it arrives: https://amzn.to/2EkAHWL

Make sure all of your battery cables are tight and in good condition. WJ grand Cherokees can be very finicky. I was having similar issues on my 4.7L. Replaced the cam and crank positions sensors three times. When I upgraded my battery cables the issue seemed to go away.

Also check that all of your grounding straps are intact. If you search the forum there is a post regarding grounding strap locations.

My battery terminals are actually very dirty ( ), I'll figure out how to clean them and do it this week. Should I just change the cables while I'm at it?

Agree on checking/cleaning your grounds, particularly the G103 PCM grounds on the passenger side engine block. Not only do the 2 PCM grounds (black/tan & black/white) attach to the G103 location but so does one of the 6-gauge negative battery ground cables. You can see where G103 is located on the 4.0 in the below ground write-up. Unfortunately not all images show up due to some forum quirk which has been going on for months.

https://www.jeepforum.com/forum/f310/jeep-wj-ground-write-up-info-4192594/#post39199282

The PCM supplies ground to all engine compartment sensors via the black/light blue wire. If your PCM ground is corroded/oily it can affect or damage the sensors along with the PCM itself. That's why it's so critical to keep this G103 ground good/clean. Good luck.

Thanks for the link! Seems like the G103 ground is underneath the car, I'll need to buy a floor jack (I guess this one: https://amzn.to/2RNXsF9) to check and clean these.

 

were there any codes? post ALL codes

Don't remember what code says- the camshaft position sensor was bad.

Does the issue only appear when stopping- Is it stumbling as you break to stop?

 

Make sure all of your battery cables are tight and in good condition. WJ grand Cherokees can be very finicky. I was having similar issues on my 4.7L. Replaced the cam and crank positions sensors three times. When I upgraded my battery cables the issue seemed to go away.

Also check that all of your grounding straps are intact. If you search the forum there is a post regarding grounding strap locations.

 

Agree on checking/cleaning your grounds, particularly the G103 PCM grounds on the passenger side engine block. Not only do the 2 PCM grounds (black/tan & black/white) attach to the G103 location but so does one of the 6-gauge negative battery ground cables. You can see where G103 is located on the 4.0 in the below ground write-up. Unfortunately not all images show up due to some forum quirk which has been going on for months.

https://www.jeepforum.com/forum/f310/jeep-wj-ground-write-up-info-4192594/#post39199282

The PCM supplies ground to all engine compartment sensors via the black/light blue wire. If your PCM ground is corroded/oily it can affect or damage the sensors along with the PCM itself. That's why it's so critical to keep this G103 ground good/clean. Good luck.

 

Also cleaning it and adding dielectric grease did not help, I'll have all the stuff to look under the car on Monday.

 

I just lifted my Jeep and am trying to follow the directions in Uniblurbs guide, however I can't seem to find the G103 ground anywhere. I looked directly under the front, from the right side to get a different view and still can't seem to find it. Could someone help me please? I took a video of what I'm looking at:

 

Pretty sure I found it, this is what I ended up cleaning off:

Now that it's cleaned my car won't start, I think it may be because I damaged this while removing the negative part of the battery:

I'm going to have one last guy come look at my car (the past two gave up), and then I may have to call it quits.

 

if other diagram is not showing - hope these diagrams will.

POST all codes

tell us do you have a scanner?

which sensor did shop switch a second time?

 

if other diagram is not showing - hope these diagrams will.

POST all codes

tell us do you have a scanner?

which sensor did shop switch a second time?

Yep looking at that diagram I do believe I found and cleaned the G103 ground.

I do have a scanner, but since the car will no longer start it won't read the service engine codes.

I switched out the crankshaft position sensor once, and the camshaft position sensor three times.

 

you should be able to read codes KOEO.

do you remember the code? p1391 or ?n

 

Yeah, that is the G103 ground and good photo! On that double eyelet the black/tan & black/white wires are the 2 PCM grounds. The black/light green & black/orange wires are to the data link connector. This is the connector under the dash you plug a scanner/reader into for retrieving fault codes.

Did you clean the oil/corrosion off of that stainless double eyelet where the wires attach? This is critical since the PCM supplies ground to all the sensors. Plus a scanner can't communicate with the PCM if the data link connector wires aren't making good contact.

While your battery terminal doesn't look the best I can't seen anything you broke? You probably could use a new terminal bolt/nut for now and may need new cables sometime. Is your battery good?

Is it cranking over and do you have the CEL (check engine light) on for 2-3 seconds like it's supposed to? Sorry it's not starting and cleaning the grounds isn't supposed to cause any further problems. Or is this from your past sensor problems?

Thought I'd post your photo below of the G103 ground on your 4.0.

 

I'd do a negative side voltage drop test. Battery negative to that engine ground/starter post and crank the engine. That cable looks a little sketchy in the pic, and there could be corrosion creeping up inside the insulation. These things are notorious for bad grounds causing a whole lot of issues.

 

Reviving this for my own G103 issue (maybe). What would be the best way to repair/replace the double eyelet ground. Mine is missing the rubber for about an inch on both wires. With a ground would it be okay to splice a larger wire into the loom?

 

It shouldn't hurt to splice a wire/eyelet into the loom to clean that mess up some. Make sure all the oil & any corrosion is cleaned off the wire/ground and check that you don't have oil leaking back onto the ground.

 

It shouldn't hurt to splice a wire/eyelet into the loom to clean that mess up some. Make sure all the oil & any corrosion is cleaned off the wire/ground and check that you don't have oil leaking back onto the ground.

It shouldn't hurt to splice a wire/eyelet into the loom to clean that mess up some. Make sure all the oil & any corrosion is cleaned off the wire/ground and check that you don't have oil leaking back onto the ground.

Thanks, glad you are still around!

 

Ha, Ha, thanks, and you're welcome!

 

Well I cut two out and spliced in new with ring connectors. The Blk/wht and Blk/tan were both missing the sheathing at the end and then the rubber was wrinkled about 6” up. I peeled the rubber off, the copper showed discoloration for about 3”. Don’t know if will cure my problems but it atleast needed to be done. Weird thing is the wires on the upper prong didn’t have the same issues, so I’ve left them for now.