PCM pondering

[Gary Allan]

I've recently had a number of anomalies occur in my 02 Wrangler.


One night in the single digit temps I started the jeep and I found my odometer reading being displayed. I always leave it on the trip odometer. Flipping to it, it was found to be @ 0.0. The radio, while retaining its presets, was on AM and at 500khtz. End of story ..shrugged and moved on.

I had my wife drive the jeep to put some mileage on the 0w-10 with her 50mpd commute. On the second or third day she reported a CEL and quickly confirmed that all the gauge indications were normal (oil and whatnot were good).

Upon scanning it, it was found to be "Cold too long" in the FSM. I told her not to idle it before leaving work in teasing her. She asserted that she did not ..I said Liar-liar-liar

since I could drive it less than a mile and reach almost normal operating temp. Her cycle before getting on the highway would be longer ..therefore it should not have occurred.

I then encountered the same event a couple of weeks later. Teh gauge didn't appear to be low, but at one point the CEL came on and you could hear the engine change. I'm speculating that it came out of fuel enrichment. Now my spider sense is tingling. I apologized to my wife (this is not always wise- opportunity presented).

Move to two nights ago. I go out to start the jeep and NOTHING. Turning the key yields ZIP. I then open the door and as the dome light gets triggered - Sha-ZAEIM (said like Gommer Pyle) everything comes back.

I don't think that I have a BCM (body control module) ..maybe I do ..but there are a few body functions that appear to be integrated into the PCM. For example, if I leave my lights on, when I open the door and the dome light turns on, the high beam indicator will blink with the chime. My dome light also turns on when I turn off the key.

Even if this was a faulty BCM (if indeed I have one) I can't see how this would relate to the too cold too long issue and I can't manage to see how they're not related.

 

[Win]

Since your car is an '02, I would get a can of a GOOD electrical contact cleaner like DeOxit, and break open every electrical connector you can find on the vehicle, and clean it with the DeOxit.

WD40 will work in a pinch, but DeOxit is the top of the line.

That will probably cure your glitches, and cleaning the electrics is necessaary PM on modern cars, anyway.

 

[javacontour]

Not to mention GROUND connections. Things get crazy when you have bad grounds.

I'd start there if you don't want to open every connection. Just start with the grounds and see if things get better.

 

[brianl703]

How's the battery? Has it passed a load test recently?

 

[javacontour]

Good point. You can have a lot of strange things happen because the battery is flaky. Maybe it has an intermittent open circuit. Maybe just a loose battery cable?

 

[asamek]

+ another on the loose battery cable.

My wife's Regal did awfully strange things until I figured out the problem!

 

[Papa Bear]

Sounds like a case of "fuzzy logic".

 

[Gary Allan]

The battery is brand new. An Interstate Megatron (Johnson Controls). I probably could have made it through the winter with the OEM, but at nearly 8 years I bit the bullet.

The first event was with the old battery ..maybe all except the nada event and my CEL episode. If it was the old battery, these sort of things can happen with a shorted battery. I've had that before. 3 on one vehicle. You can have all kinds of strange stuff with that.

Normally I would look for grounds if something didn't work (which the nada event was) but everything is 100% functional 24/7/365 ..bumps ..jars ...you name it. This screams electronic more than electrical ..but I'll go through the usual suspects anyway.

Lots of connectors ..not as many grounds...



Riddle this one: 1986 Tempo, bought new. The driver side head light would burn out. Then, without warning and 100% transparent except for the fail event, the car would not crank. When the key was turned on, the tach would go to full scale deflection ..various things didn't work (radio, etc.). Sit for a bit, the car would start normally and everything would be fine. The warning of the shorted battery was when the driver side bulb burned out. I never managed a plausible explanation for that one. Nor could I reason that I had 3 bad batteries in a row ..OEM included ..and that the last battery (if it was the vehicle itself) lasted until I gave it away (about 6 or 7 years later).

 

[brianl703]

So the battery is new. Has it been load tested? If it passes a load test then I would move on to measuring the voltage drop in the battery cables while cranking the engine.

 

[Gary Allan]

This isn't a cranking problem. The thing cranks fine. It doesn't need to be jumped to start and this was the first time ever that nothing happened when the key was turned. When I mean NOTHING ..I mean NOTHING ..no dash indicators ..no nuttin'.

When the door opened, the dome light switch triggered something and everything came back to life. It was literally like I threw a big ON switch when I opened the door. After it was started I noticed that the radio was at 500khz and the odometer was showing the total mileage ..just like it did once before, but that event didn't have the totally dysfunctional state.

 

[The_Jeff]

Here's my musing, take it for what it's worth.

Jeeps come with these little slugs you can stick in the door pin switches so the dome stays off when you run doorless.

But I bet they aren't counting on that, and the BCM has some sort of low-voltage "lifesaver" mode that shuts the whole interior down. This could be triggered with the +12v always hot input flaking out.

 

[punisher]

Originally Posted By: javacontour
Not to mention GROUND connections. Things get crazy when you have bad grounds.


I so agree. Ck those grounds.

 

[Texan4Life]

+1 on grounds

I would focus on battery side connections.

take 30 minutes and really get after them with a wire brush and reinstall.

if that doesn't do it, clean the engine side of at least the ground cable.

 

[brianl703]

Originally Posted By: Gary Allan
After it was started I noticed that the radio was at 500khz


...which can be caused by the system voltage dropping too low while cranking the engine.

I can't think of any other reason that a radio would "forget" what station it was tuned to.

Ahh, you say, but it still had the presets..yes, many newer radios store them in EEPROM memory, so they don't get erased.

 

[Gary Allan]

Yes, it acts just like the battery has been disconnected and reconnected.

The battery cables are quite sound. Terminals cleaned and the posts scuffed at the batter install. Remember this occurred before and after a new battery install. The only difference is the NO NUTTIN' event coupled with it.

My wife's jeep has a fuse you pull to defeat the door switches. I'm pretty sure I do too.

Again, no anomalies whatsoever in regards to blinking lights ..drop outs ..stuff not working. All lights work as they're supposed to ..fan, radio, wipers, brake lights ..signals, horn ..and all flawlessly. Aside from the "cold too long" any and all of this was when going from nothing to ON. The second time with nothing happening.

My first stop is at the PDC (power distribution center) to check the relays.

..but I do thank you for the suggestions. I've learned too many times that thinking that you've got it covered since the symptoms don't match the common ones associated with the common remedy is a sure way to miss the problem.

 

[mechtech2]

STart with your cable ends and grounds.
There are often extra body/chassis grounds, and a special ground to the computer.

[It could also be 0-10 poisoning!]

 

[brianl703]

I think a bad ground could definitely cause this problem, forcing the heavy starting current to go through alternate ground paths(which aren't big enough), which could cause voltage drop.

 

[Gary Allan]

Originally Posted By: brianl703
I think a bad ground could definitely cause this problem, forcing the heavy starting current to go through alternate ground paths(which aren't big enough), which could cause voltage drop.


Sitting still with the key in the ON position and not turning it to START?

..but (

) since many feel that the starter can be contributing to this, the thing did draw higher than it should when tested at the time I put the new battery in. But from the sequence of events, it's a real stretch for me to associate this with the starting event. The issues had to manifest themselves after a 100% seamless driving event and only the key being shut off before the problem developed. It was then discovered before the next starting event. The cranking sequence is fine ..the post discovery (the aforementioned door trigger event being a new symptom/clue) operation was 100% functional.

..but again, I'll go through the numbers.

 

[brianl703]

You know what I would do? Measure the voltage drop between the radio chassis and the car battery negative while starting the engine.

Then do it for the radio memory wire and the car battery positive, again while cranking.

There's a flaky connection somewhere. Voltage drop testing will find it.

The act of opening the door could have jiggled that flaky connection so it worked.

 

[Gary Allan]

Yeah, I think that it triggered some relay. These things, as simple as mine is, are too complicated for the tasks performed.

I hope I can stall this until it's not so cold. I can see myself in the unheated garage waiting for the LCD display to catch up

Another possibility is the ignition switch itself. It's got about 8 or 9 leads to it. After having the drive piece between the lock cylinder and the actual switch break, I find it odd that more of these jeeps aren't stolen if not equipped with the coded key. It's much easier with the key to remove the lock cylinder, but I'm pretty sure you just undo the facia pieces ..break the column lock (it's grey metal encased in plastic) and a couple of fasteners has the ignition switch hanging in the breeze with it's simple square drive waiting for a key or screw driver to start the thing.

This may be the faulty connection. When you open the door the odometer lights up ..as it does with turning the key to the ON position (as well as the indicator bulbs).