I think the new Jeep needs a new PCM - best option?

I recently bought a 2005 Jeep Grand Cherokee hemi from another grmer.

Drove it home from NJ to Chicago. Check engine light came on on the highway, went off next day. 

Following day, AC doesnt work. Day after that I take it for a car wash and stop at Auto parts store for a can of refrigerant (I made an assumption about the AC). When I get home car can't idle and check engine is flashing. Running super rough. Codes for all four o2 sensor heating circuits (p0031,37,51,57), and p0300 for random misfire. Blast.

Took a few days and did some examination. From what I can find, the O2 heater low codes are one trip set and three good tests clear. So very odd that all 4 trigger at the same time. I did check they all have the same ground and it is connected to ground (but the low fault would be caused by short to ground before the O2, not short to high or broken ground after). Unplugged all 4 PCM connections and check for junk and reconnected, since the power to the O2 heaters comes directly from the PCM.

There was some jank alarm system and accessory light harness installed partially (including power to the system coming from a splice into the number 8 coil power wire...), and I took the rest of it out. Reset trouble codes. Car drives great. AC works. Let it come up to temp, did a few key cycles, drove to local grocery store and back, no issues, no cel. I think I have it licked.

Go outside tonight to move cars in driveway. Instant cel. Service 4wd messages on dash. Can't idle. Surging like crazy. Stalling, hard to back up. Get the code reader and sure enough same 4 02 heater codes. But RIGHT after startup, shouldn't be using O2 signals yet anyway, so that wouldn't explain the poor running.

Anyway, I guess it is a common problem for these PCM to have internal issues that can cause similar outcomes. I'll probably do a quick check of the 4 o2 heater resistances to make sure they are in spec, but again I can't imagine 4 simultaneous failures, fixes, and re-failures. I have the PCM pinout and can check the O2 heater power wires don't connect to ground as well.

So, if I think it's the PCM:

1. Do I try to pry it apart and look for broken or sketchy solder joints?

2. Do I buy a used one on eBay (I think I'll have to then get it flashed by someone with the capabilty)?

3. Do I buy one from a refurbisher? Looks like prices from $250-$400 or so. Any recommendations?

4. Dealer?

Check with the folks at verticalvisions.com.  It looks like their knowledge is with 2007-2016 model years, but they may have some insight.  I've had one of their test/bypass cables on my 2011 Town and Country for about 8 months and will be getting one of the plug-in bypass systems to help with cold start issues this winter.  I wonder if water got where it wasn't supposed to during the car wash?  Good Luck!  

chrispy said:

  I wonder if water got where it wasn't supposed to during the car wash?  Good Luck!  

I thought maybe that was an issue as well, but no water has touched the car since it was running great a few nights ago, and then suddenly it ran like crapola.

According to our diag software here there was 4 reported cases of all those codes together and they were all solved by a PCM replacement.

I'd always check dealer prices first, it may be stupidly cheap. You will probably have to do some key reprogramming/ security parameter reset when the PCM is changed

psychic_mechanic said:

According to our diag software here there was 4 reported cases of all those codes together and they were all solved by a PCM replacement.

I'd always check dealer prices first, it may be stupidly cheap. You will probably have to do some key reprogramming/ security parameter reset when the PCM is changed

THAT is a great vote of confidence for my diag skills.

Sorry, I feel like an idiot but I never witnessed anything like that. Stuff like the AC not working or the idle being rough is just something I never experienced ever in 3 years so I am at a loss.

I think most if not all 4 O2 are new but not all at the same time or anything like that, just normal replacements as needed. I can't make any real sense of their odd behavior.

Never seen the random misfire code. 

My thoughts on the janky wires from the previous owner was that since I never had an issue I never got around to touching them... definitely good idea to take em out now...

I have seen the "service 4wd" message maybe once a year? I read that it was a known electrical glitch since everything worked fine.

My first thought is simple; check all grounds all over. I cannot diagnose electrics any better than a common raccoon and that is where I always start. They are essentially wear items on that car and I never replaced them all, just a couple iirc.

I was happy that I didn't see a broke down on the road thread, but now I kinda feel like crap. Probably some of you can relate because I trusted that car; turns out that was a mistake. I have had good luck with refurbished electrics when I need something like this, lmk if you want me to buy you a pcm?

In reply to tb :

meh. Sometimes crap just happens, tis life with used cars (esp for challenge budget). If it turns out to be the PCM, you can buy me a beer at the challenge!

In reply to Robbie :

Cool. I know you understand the joy of buying and selling cheap crap probably better than I do. I'm just shocked since I trusted it daily and cut the price to make a clean break, not because I thought it was a time bomb. 

Sorry it is turning into a headache. I'll follow along to see what happens and I sincerely hope it is something incredibly simple...

They always pull that crap when you sell them to a friend...or right before.  

tb said:

In reply to Robbie :

Cool. I know you understand the joy of buying and selling cheap crap probably better than I do. I'm just shocked since I trusted it daily and cut the price to make a clean break, not because I thought it was a time bomb. 

 

Sorry it is turning into a headache. I'll follow along to see what happens and I sincerely hope it is something incredibly simple...

screen name "tb", denies knowledge of vehicle being a Time Bomb.   hmmmm....

i keed, i keed!  ;-)

Well, refurbished PCM is here and installed. No problems (seems fixed) so far. I will wait a couple more days and try to drive it as much as possible to make the final call however.

re: The water comment, it does seem like there is pretty good potential for water to get on the PCM in its factory location. And I don't see any factory covers or shields for it in any online pictures, so I hope the PCMs are waterproofed in their cases.

The bad news is that wifey and I are probably forced to sell it. It just won't be able to work as a family truckster for us. The biggest reason is it seems to make my wife carsick (we have had one or two other vehicles before do this to her), so that is just a no-go unfortunately. It doesn't make sense for me to keep this around to just sit there while we drive a different vehicle, so I think the best is to move it on down the road (hopefully with no more PCM issues!)