HI everyone. I have an electrical issue with my 2000 cherokee xj sport. When I hit a big pot hole with my passenger front tire my ecu resets (check engine light disappears for a while) radio restarts (please note it is not getting reset to factory settings but just turns on and off). I've checked battery to body ground, engine grounds, engine to body ground, pdc power and grounds on driver side fender near air intake box and everything looks tight. sprayed ecu connectors with wd 40 for electrical contacts but no results. I was wondering if someone had the same issue or maybe can tell me where else should I check. Thank you!

 

Sounds exactly like a loose battery connection, but if you're certain the cable clamps are in good condition and tight I'd be looking at the wiring and seeing if there's something chaffed or exposed.

 

@PatHenry Thank you. I will take a look one more time and make sure that everything looks fine.

 

Take apart the ECU and look for broken solder joints.

Example of what to look for:


Going crazy:

https://www.jeepforum.com/forum/f13/...tures-1303589/

 

@Dave51 I thought it might me ECU. I just wasn't sure it could affect the radio. Do you think it can?

 

Sure. I'll bet you've checked all the grounds and scrubbed them up a million times already. You seem like a savvy guy so you already reset all the fuses and relays.

My guess is that other things happen during this event but you haven't noticed them.

As unrelated as the 2 events seem, there is one system where they are - Ignition Off Draw. And within that system the wires are not particularly vulnerable, so IMO the weakest link would be a solder joint.

Admittedly this theory requires a little artistic license, but when you have eliminated all other possibilities, whatever remains, however improbable, must be the solution.

 

I agree with you I will unscrew it today and will shake it to try to reproduce the issue. I didn't mention that problem began when engine was replaced. so I believe it is in engine compartment somewhere but not ecu (wasn't replaced with the engine). I also notice yesterday that gudge arrows are going down when it is happening. Maybe it is a g108 ground?

 

How is your battery tie down? Does the battery hit the hood when you hit potholes causing it to ground out for a second?

 

tied down with original metal clamp I checked positive and negative battery clamps and everything is perfect.

 

Well almost.

In an effort to get my post count up

In an effort to add additional information, a troubleshooting aid could be turn on the visor vanity lights and the dome light and see if they wink out when this happens.

Fuse 16 is like the switch for this function, but don't just rip it out there's a procedure for that (ignition has to be off)

I cannot find the IOD/ECU connection in the wiring schematics yet, but given the draw of the ECU memory it has to be there somewhere.

Regardless, IMO checking the ECU for cold/broken solder joints would be a good idea, especially if all other avenues turn into dead ends.

 

Ok thank you for this reply now I think I got a little closer. So IOD (Ignition off draw) is like a memory for the car same as a battery for BIOS in computer. So it makes sense that short or power loss in that system can cause ECU to forget and ratio to restart. I will print out schematics and will try to find an issue.

 

It goes to c1 connector in junction box and from c4 (not sure what s18 means) to radio and instrument cluster. I will pull out and inspect junction box tomorrow

 

Not exactly. The IOD fuse (you have to yank it out) will turn off devices that use power even if the car is turned off so during long term storage the battery will not go dead. On that list is the ECU:



So here's where the artistic license comes in (and I'm trying to read into your description):

After an apparent interruption in power, the ECU and radio reboot. Not go dead, reboot. If the ECU lost power you would have come to a screeching halt (but tell me if you did).

Only the radio and ECU were affected. TTBOMK, the only circuit that that could possibly occur in is IOD.

Other devices on the XJ include door locks, vanity lights under the visors, the underhood engine light.

But I don't think Fuse 16 acts like a switch for all those devices. Rather, the overall control should be by the ECU, hence, search for a broken solder connection there.

Of course, there could be something wrong in the PDC, but if the fuse was bad all the stuff would be off.

And anyway, my thought is if there's a problem with the ECU, start with the ECU.

 

So although FSM says the PCM is on the IOD circuit, where is it in the schematic?

A sidebar, in 2002 Chrysler applied for a patent for a system where the ECU takes over the function of Fuse 16:

https://patents.google.com/patent/US6759760B2/en

Interesting or what?

 

There is only one way to find out. Pull out the IOD fuse and see if check engine light will disappear.