99 Caravan - Won't Start. PCM?

start
dodge
caravan
computers

#1

Symptoms - Started up about 6 or 7 times, but shut down immediately. Now, won’t even crank. Dash doesn not register - No Mileage, No Gas, No Digital Odometer, etc. Onboard computer registers Compass and Temperature correctly, but no Mileage, DTE, Time, etc. Radio works, Power Equipment Works, Remote Works, Fuses test all good. Disconnected and re-connected Battery, but to no avail. Any suggestions?


#2

It probably won’t crank because the battery is dead. Step 1 get the battery checked, check connections and since I am guessing your old battery will be fried start by replacing the battery, see what happens and get back to us.


#3

Sounds to me like you have a dead battery.

Have you had the battery “load tested?”


#4

Thanks for the reply. I will load-test it tomorrow just to eliminate this as a possibility. When it did crank, it cranked with full power, and started briefly. It would then deliberately shut itself down. (Believe me - I could give it gas and rev it, then it would just cut power - Auto-shut-down relay???)

Anyway, full power to all lights, radio, accessories, etc. - no sign of low voltage. Still, since the odometer, clock, mileage, and gauges fail to register, I’m lead to believe it’s computer related.

Will get back on this in the morning.


#5

See my response to waterboy. I’ll load-test it in the morning, but all evidence says battery is good, and only computer-related instruments are affected.

I’ll let you know soon.

As always, thanks for the reply!


#6

What is happening during crank, that’s not there during idle (which is the moment you release the key from START?
The fuel pump is powered by a different contact in the ignition switch, for a couple of seconds, when the key is turned to START (and, maybe, a different circuit through the PCM).
Got fuel pressure tester? Use the fuel pressure tester to see if there is fuel pressure when the ignition key is turned to RUN (not to Start).


#7

Update - 24 Hrs later, I head out there with my meters, to prove it’s not the battery, and also to listen for the priming of the fuel pump (I can hear this) as hellokit suggests.

Silly thing registers all the instruments and starts right up!

Well, I guess it’s running now. Fluke?

I’m still curious as to what happened. Seriously, as someone who inspite of my electrical engineering degree, has been fooled by car batteries on multiple occations, I am quite certain this was NOT the battery. Full power to all components, except instrument cluster - no odometer, no gas gauge, no mileage calculations, etc. I think my computer went on vacation for 24 hours. Is this a symptom of a fading PCM, or just a fluke?

Thanks to all who replied, and anyone who can get past my ego and give me any additional input!

-Jason


#8

Is there a way YOU can (without going to a dealer) test the PCM to see if a fault is registered? (Just shootin’ in the dark)

To add: perhaps there is an ignition system problem like maybe a bad ground/connection somewhere? Trouble here is finding a fault when the system is working. No codes?


#9

There are several switches between the battery and the starter solenoid: ignition switch, neutral safety switch, maybe a starter switch, starter solenoid. A switch can fail to make a connection any time it darn well pleases. This is an intermittent action—sometimes, it is, and sometimes, it ain’t. Since power for the dash lights comes from the ignition switch, that’s my first suspect.

Addum: And a switch can break a connection, already made, any time it darn well pleases, and as often as it wishes.


#10

That’s a good question. How do I get the codes? (I did the switch the key from on to off fifty times and wait for the light, but I think this vehicle might be too new for that.) Maybe I should just invest in the OBDII interface. They’re pretty cheap now.

Thanks for the suggestion.


#11

OP may want to bring this issue up at allpar.com’s minivan forum, which is devoted to Chrysler Corp. minivans.


#12

I agree with Hellokit and the OP, the trouble isn’t with the battery you need to check for a problem with the switches and power connections to them before blaming the PCM or BCM. I think the BCM controls a lot of the things you mentioned weren’t working though. A lot of folks think the computers are at fault when these kind of problems occur but thet are really fairly reliable and should be near the end of the check list for a problem. When they do go bad it isn’t an intermittent problem usually. Always start the hunt for problems like this by checking for trouble with power delivery to the affected areas and the simple things first. Then move on to other areas if those things check out ok. Most problems like this are due to faulty ignition switches, relays, or bad wire connections in the power leads.

I suggest you purchase a factory service manual since you can use it. You will find that the help it provides you is well worth the cost. Using the manual to help solve this problem alone will justify the cost of it over taking it to a shop.

Looking at some data for the van it shows that a automatic shutdown relay may be a suspect. It is in the power distribution center under the hood and supplied power through fuse 17 a 20A fuse. When the trouble happens again you might try tapping on it to see if that makes a difference. If you have a similair one in the panel you could try swapping them.


#13

All good suggestions. I don’t know for sure if the 'AutoShutdown relay will kill the inst panel. verify Ignition switch first. with car running, jiggle key, move it around without turning it.


#14

I did some rechecking of the data and I made a mistake about the way the power runs from the AutoShutdown relay. Thanks Txtinkerer for questioning my statement about the instrument panel. The relay does not power the instrument panel like I thought it did.

If the trouble is still occuring check fuse 2 in the junction panel (the dash area) and see if you have power there when the ignition switch is ON. If not, there is a dark green/red wire from the ignition switch that carries power to the fuse. That section of the switch may be bad.