No OBDII comm + PCM swap

[hbar..]

Have a 99 XJ that won't communicate on the OBDII port. Code reader powers up, goes through its cycle, and then says it won't communicate. Did all the standard troubleshooting steps but could not make it talk.

Then we put in a computer from a 2000 XJ just to see, and sure enough it communicated, so we've basically proved it's not a wiring or grounding problem. It seems to be that the original computer is the culprit.

The "new" computer is from a 2000 (ours is a 99), but both were autos, a/c, 4wd, same gear ratio....not sure what all matters when it comes to this stuff. (A) can I drive it with the 'wrong' computer and (B) how much damage can I cause by doing so?

 

[lawsoncl]

Should be fine with the 2000 computer. You might have an issue if the vin in the computer doesn't match during an emissions check though.

 

[hbar..]

Should be fine with the 2000 computer. You might have an issue if the vin in the computer doesn't match during an emissions check though.

This particular vehicle got through the Texas inspection by paying a $75 (cash) convenience fee. The VIN must not be too big a problem because the vehicle he connected the computer during the XJ inspection was not an XJ.

But I wouldn't think the VIN would be too big an issue...I mean parts get replaced all the time. And have you seen the people doing vehicle inspections? No way they're physically looking at the dash & writing down the VIN when the computer will give it to them.

 

[lawsoncl]

I would hope they go by the VIN on the dash, since that's what matches your registration.

 

[Cummins90]

If the 2000 ecu is a coil pack ignition how will it fire the single coil distributor on the 99?

 

[lawsoncl]

If the 2000 ecu is a coil pack ignition how will it fire the single coil distributor on the 99?

Excellent question!

 

[hbar..]

If the 2000 ecu is a coil pack ignition how will it fire the single coil distributor on the 99?

You may be onto something. Plugged it in, ran real rough and threw a p0352 & p0353, ignition coils b & c. In some ways it's an improvement, since now at least we can read codes. But with the 1999 computer it runs much smoother, but no OBDII communication = no pass TX inspection.

In a perfect world we could just fix the communication problem on the computer. It's not a bad ground or CPS or any of the usual suspects since the 2000 computer is able to communicate.

 

[Tim_MN]

If you are certain the original PCM is faulty, a used 98 or 99 PCM should fix it. Unless you need the VIN to match for Emissions Testing, the donor PCM does not need re-programming.

 

[hbar..]

If you are certain the original PCM is faulty, a used 98 or 99 PCM should fix it. Unless you need the VIN to match for Emissions Testing, the donor PCM does not need re-programming.

I'm confident of two things and two things only: (1) that with the current computer it runs pretty well but will not communicate on the OBDII port, and (2) with the 2000 computer it runs super rough but will communicate on the OBDII port.

This pretty much tells me that there are no strange grounding issues, shorts, or broken wires in the harness or plug preventing communication. If that were the case, the 2000 wouldn't communicate either. :attom:

 

[Tim_MN]

I do not recommend random parts swapping unless for diagnostic reasons, and if the parts cost is reasonable. There is no do it yourself PCM diagnostic. Around here, a good used PCM is $22, so swapping one or having a spare is a good low cost idea.

Tech note: 97-01 Cherokee with the factory installed SKIM/SKIS key-in-chip system MUST have the key reader device disabled before swapping any PCM's, or the system will suspect a theft attempt and permanently lock up the "new" PCM.

 

[Cummins90]

Sentry lock usually takes 3 start attempts with failed sync on the ngc3 is it the same with the JTEC+? The dealer can unlock the PCM or if you know some cool people they can also unlock it or disable the skim completely.

 

[hbar..]

I do not recommend random parts swapping unless for diagnostic reasons, and if the parts cost is reasonable. There is no do it yourself PCM diagnostic. Around here, a good used PCM is $22, so swapping one or having a spare is a good low cost idea.

Tech note: 97-01 Cherokee with the factory installed SKIM/SKIS key-in-chip system MUST have the key reader device disabled before swapping any PCM's, or the system will suspect a theft attempt and permanently lock up the "new" PCM.

No skim on this jeep, and the "random parts swapping" was really to see if the communication issue was wiring on PCM.

I'm happy to pay you $22 + s/h for a good used PCM for a non-skim 99 auto, we've had no luck finding anything locally.

 

[RCP Phx]

I've had good luck with 3 2000 PCM's from these guys......
https://www.fs1inc.com/1999-jeep-cherokee-engine-computer-pcm-ecm-ecu-programmed.html?gclid=Cj0KCQiA95aRBhCsARIsAC2xvfwSVJzTibBe0hg7y6BFTZp7vrv1fptfmr6nFSaqdCMqPYnYtIk9hm8aAvrjEALw_wcB