Dodge starts with scan tool plugged in

[Scout1]

Need some help here. 1999 Dodge Caravan 3.8L Suddenly wouldn't start with a lot of electrical "strangeness". Starter just clicks but lights stay on. Jumped it but no change so it's not a dead battery. Dash lights act funny - off and on. Clicking from the relays in the fuse box.

Now the strange part. I hooked up my scan tool and it doesn't have any codes. But I tried to start the van with the tool hooked up and it started! Didn't run very well with the RPM taking momentary drops and the gauges reading sporadically, but it ran. Unplug the scan tool and the motor dies and won't start. Plug in the scan tool and it runs again.

Anybody know what the heck is going on???

 

[yonyon]

Loose battery cables?

 

[JimPghPA]

The battery could still be bad or discharged.

 

[The_Eric]

Sounds like a ground or power issue. Backfeeding through the scan tool at the data port.

 

[SwampSurvivor]

I would check grounds and then check the battery cables. For some reason, Chrysler electrical systems do strange things if the battery isn't completely right.

 

[eljefino]

Originally Posted By: The_Eric
Sounds like a ground or power issue. Backfeeding through the scan tool at the data port.


Yeah this. Pins 4 & 5 are getting connected. One is chassis ground, one PCM.

If you want to do a cool parlor trick, figure out which of these two will have the car run when grounded elsewhere.

Also check for a bad main power feed at the HVAC fan switch. Could be burnt plastic from overheating undersized wires/ contacts.

 

[Scout1]

It's not the battery cables, I cleaned them when I removed them. Actually, I had to remove them when after trying to start it the shutdown relay continued to click even with the key off.

Pins 4 & 5, you mean on the scan tool port? I guess I'm a little fuzzy about how to "check the grounds"... where would you look? The idea of grounding through the scan tool makes sense.

Could it be one of the relays is bad in the fuse box?

 

[eljefino]

Yeah I meant on the OBDII port. To "prove" this, take your scan tool and probe its two pins 4 & 5 with an ohm meter, you will find zero ohms.

If you follow a chrysler schematic you'll see a fairly elaborate PCM grounding system that generally ends at a rusty bolt.

I'd go to town under the hood finding grounds and polishing them up.

The relays are just responding to their crackhead inputs.

The body control module may also have a piece of the culpability.

Also pull a couple of your sensors and look for the computers +8 and +5 volts. Any sensor that's nearly shorted can drag down this voltage and the other sensors will return bad data. You could even try running without non essential sensors to see if things improve.

 

[Scout1]

Thanks. What's a "body control module"? I thought everything on these Dodges was controlled by the one computer...Is there another? Any tips on where it would be located? The main computer I believe is on the drivers side front wheel well.

 

[clinebarger]

Originally Posted By: Scout1
Need some help here. 1999 Dodge Caravan 3.8L Suddenly wouldn't start with a lot of electrical "strangeness". Starter just clicks but lights stay on. Jumped it but no change so it's not a dead battery. Dash lights act funny - off and on. Clicking from the relays in the fuse box.

Now the strange part. I hooked up my scan tool and it doesn't have any codes. But I tried to start the van with the tool hooked up and it started! Didn't run very well with the RPM taking momentary drops and the gauges reading sporadically, but it ran. Unplug the scan tool and the motor dies and won't start. Plug in the scan tool and it runs again.

Anybody know what the heck is going on???


First thing we need to do is narrow this down, The OBD port has 2 separate ground circuits, Pin 4 & Pin 5, Pin 5 is on the same ground as the PCM. Pin 4 is on a separate ground circuit, The Scanner is most likely "Jumping" the grounds together supplying Pin 5 with a ground.

Jumping Pins 4 & 5 with a paper clip should make it run, If so you have a bad ground.

 

[mount]

Originally Posted By: Scout1
Need some help here. 1999 Dodge Caravan 3.8L Suddenly wouldn't start with a lot of electrical "strangeness". Starter just clicks but lights stay on. Jumped it but no change so it's not a dead battery. Dash lights act funny - off and on. Clicking from the relays in the fuse box.

Now the strange part. I hooked up my scan tool and it doesn't have any codes. But I tried to start the van with the tool hooked up and it started! Didn't run very well with the RPM taking momentary drops and the gauges reading sporadically, but it ran. Unplug the scan tool and the motor dies and won't start. Plug in the scan tool and it runs again.

Anybody know what the heck is going on???

I'm assuming you replicated this more than just once?

 

[mene]

OK. Like eljefino mention check the wiring behind the A/C control panel, I know, I know, What has that to do with this? do it, specially the fan socket, after that very forcefully hit the top of the dash and try again, you might be surprised. Also, those grounds, there is one in the back of the engine IIRC not easy to see, check that one too. Best of luck and keep us posted.

 

[earlyre]

unless i'm mistaken, that vintage caravan had all kinds of electrical gremlins from poor quality early lead free solder. they also had myriad issues with bad clocksprings, but if you have the clocksprings relaced, they have a lifetime waranty.
here's a thread where i asked about known/"usual" problems with y2k caravan (99 is same gen IIRC) that a friend had gotten for free.
http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/2679441

see the 3rd reply, which happens to be from eljefino, who posted already in THIS thread.

 

[Scout1]

Ground behind the engine eh? Might be worth looking into; last summer I spent the better part of a day rummaging around back there changing the spark plugs (the van only has 97k miles on it - I'm the original owner). Maybe I knocked something loose?

I had another no-start episode I posted a few months back. It was different than this time since then the engine would crank, just not start. Conclusion back then was flooded engine but I'm wondering if it all ties together to an intermittent ground somewhere. Strange thing is it runs perfectly between events.

Oh, and yes to the other poster, I duplicated the start with the scan tool connected twice to convince myself it was directly related to the scan tool being hooked up. Wouldn't run without it plugged in.

 

[Michael_P]

Still could be the cables. The corrosion and oxidation can occur under the insulation. Ive seen it before. Take a jumper cable from the negative battery post to a ground on the engine and or chassis.

 

[Scout1]

Fixed!!!

Took everyone's good advice and went out today to check/clean the grounds. Started by taking a good look at the battery cables. On the negative post, there is a smaller wire held on by the pinch bolt... looked kind of rusty/junky. So I took my jumper cables and hooked up the negative post to this little wire and she started right up! Removed my jumper cables and "click...click...click" dead! Hooked em' up again and started right up. Found my problem me-thinks! So 5 minutes of sanding, a bit of dielectric grease and she's back to normal.

Thanks for the advice gang, you guys rock!!! I did some reading on the Chrysler forums and found a lot of people had similar symptoms to mine and very frustrated; towing to the dealer, replacing PCM's etc. etc. I was lucky to find the problem at my battery terminal but I wonder how many others have spent lots of $$$ chasing this ghost?

 

[mene]

Originally Posted By: Scout1
Fixed!!!

Took everyone's good advice and went out today to check/clean the grounds. Started by taking a good look at the battery cables. On the negative post, there is a smaller wire held on by the pinch bolt... looked kind of rusty/junky. So I took my jumper cables and hooked up the negative post to this little wire and she started right up! Removed my jumper cables and "click...click...click" dead! Hooked em' up again and started right up. Found my problem me-thinks! So 5 minutes of sanding, a bit of dielectric grease and she's back to normal.

Thanks for the advice gang, you guys rock!!! I did some reading on the Chrysler forums and found a lot of people had similar symptoms to mine and very frustrated; towing to the dealer, replacing PCM's etc. etc. I was lucky to find the problem at my battery terminal but I wonder how many others have spent lots of $$$ chasing this ghost?


Visit the Chrysler minivan forum, you will find lots of answer for your van and if you are lucky you will learn a thing or two you didn't know about them. I'm glad is back and good luck!

 

[r2d281]

I know this post is old but I just had the same problem and I was crazy for a month, I read this posts and checked my battery cables, one of the small ground cables was cutted (I don't know how) but I didn't see it because had electrical tape on it. My 2006 town and country is working like new now.

Thanks guys!!!

 

[kc8adu]

looks intentional cut with dikes.
have had chevy trucks where cluster was dead.obvious bad steppers.dic out,ect.
rebuilt it and still dead but would test fine on the bench,do a sweep test,ect.
scantool plugged in and it comes on.bad ground every time!