johnmw

Hi guys,
I have been lurking around here for a month or so, hoping to come up with ideas to fix my old rust bucket. My 1992 Cherokee Laredo seems to have had it's computer die ( ECM or whatever it is called ). Will swapping in a known good one from a friends 92 take a chance of damaging his ?. Mine crapped out and I don't know why. I went thru all the usual tests and parts swaps, TPS, Coil, tested connections, fuses and everything else I could think of with no improvement . I just do not want to cause anyone else problems trying to fix my problem. If it keeps this up, maybe I'll just scrap it for parts here on the forum cheap.

Thanks for your time

john

freegdr

Wheres the question ?

VTJeep

so, PCM issue? you can try your buddy's, all the specs need to match as far as the two vehicles go.. but it think it goes beyond that. I've HEARD that if you have the PCM out for more that a couple hours, your in trouble. at that point it needs to be reprogrammed/replaced at a Chrysler dealership. this is what ive been told, might be wrong, might be right. either way, if you've gone thru the litany of replacing every sensor, etc. it sounds like an issue in the wiring, maybe a bad ground, maybe a corroded wire or more possibly, the PCM is bad.

johnmw

After beating my head on this thing for way too long. I bought another Auto-shutdown relay, cause a friend said these things are sometimes junk right out of the box. Sure enough, it started right up and runs great.

How often are these relays bad right outta the box ??

thanks for your time

John

PocketsEmpty

Auto-shutdown relay? That's a new one on me. What's it's purpose? Glad you figured it out.

Now, what are you going to do about the rust?

johnmw

Tell you the truth, I am not too sure what the auto-shutdown relay is for. The parts guy where I got it said it was to drive people nuts when it craps out.........

Rust is your friend ????

cruiser54

ASD relays being bad trump a bad PCM about 100 to 1. Glad you got it.

Carl48

Output from the ASD relay is the dark green/orange wire(s) which go to the alternator, ignition coil, and injectors. The ASD relay is usually pretty reliable but as you now know, if it fails the Jeep will not run.

The lesson here is not to condemn the computer or the whole vehicle until all systems have been logically troubleshot...the only way to do this is with the electrical drawings in the FSM. Fortunately, you got lucky with replacing the ASD relay.

btw...the first ASD relay may not be bad...could very well be corrosion in the relay socket in the PDC. Anyway, good luck

cruiser54

I couldn't agree more.

R*C*B*R*C= Refresh Connections Before Replacing Components.

PocketsEmpty

So, what is the darned thing actually for? I want to be aware of it in case it fails

cruiser54

I don't know cuz I'm more of a Renix guy. My suggestion would be to carry a spare. and in the meantime, remove it, clean the contacts real well, add some OxGard and reinstall it.

salad

I'm quite groggy from last night's pages, but for some reason I think that the ignition switch in RUN or START powers the relay, and the ground is connected by the PCM when it sees valid signal from the CPS. The relay lets power to the injectors and coil, and those devices are operated by the PCM grounding them.

So when you turn the key off (or lose your CPS) this relay goes dead.

PocketsEmpty

So essentially, it's an ignition relay? The term auto-shutdown seems to be a bit off-kilter for this application, unless the idea here is that it will "automatically" shut down the Jeep if the CPS goes? As a fail-safe sort of thing? Hmm...how very interesting.

salad

Okay now I'm sort of alive here's what I've got from my 1999 FSM

(Ignition section)

AUTOMATIC SHUTDOWN (ASD) RELAY

As one of its functions, the ASD relay will supply battery voltage to the ignition coil. The ground circuit for the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM regulates ASD relay operation by switching the ground circuit on-and-off.

(Fuel Injection section)

AUTO SHUTDOWN (ASD) RELAY—PCM OUTPUT

The ASD supplies battery voltage to the fuel injectors and ignition coil(s). With certain emissions packages it also supplys voltage to the oxygen sensor heating elements. The ground circuit for the coil in the ASD relay is controlled by the Powertrain Control Module (PCM). The PCM operates the relay by switching the ground circuit on and off.

AUTOMATIC SHUTDOWN (ASD) RELAY SENSE—PCM INPUT

A 12 volt signal at this input indicates to the PCM that the ASD has been activated. The ASD relay is located in the Power Distribution Center (PDC). The PDC is located in the engine compartment (Fig. 2). Refer to label on PDC cover for relay location. The relay is used to connect the oxygen sensor heater elements, ignition coil and fuel injectors to 12 volt + power supply.

This input is used only to sense that the ASD relay is energized. If the powertrain control module (PCM) does not see 12 volts at this input when the ASD should be activated, it will set a diagnostic trouble code (DTC).

I suppose yes, it automatically shuts your Jeep off if the CPS dies

Gee oh Dee

I seem to remember talk of being able to bypass it...