• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

'02-up TJ ECU in a 2000-2001 XJ

casm

NAXJA Forum User
Location
Oklahoma
I'm not really sure if this falls under Mod Tech or Street & Performance since it kind of straddles the two for what I'm looking to accomplish, but there's some overlap in both areas. If it needs to be moved to the other forum, totally understood.

Here's the basic question: will the ECU from a 2002-2006 TJ work in a 2000 or 2001 4.0 XJ? I'm concentrating on only the 2000 and 2001 XJs for this now because a) they use effectively the same ignition system as the TJ, and b) I've got a 2000 :) This may be able to be applied to earlier XJs later on, but for the sake of keeping things as simple as possible would like to stay focussed on the 2000s and '01s.

Expanding on that: this thread asked if a Mopar in-dash sat-nav unit would work in an XJ. The short answer is that it won't due to the differences in the TJ and late XJ busses - but as the bus is provided by the ECU, would an ECU swap allow the sat-nav unit to work?

I don't have a TJ FSM or ECU handy, so don't even know if the connectors are physically-compatible - it also means that I can't really look up the differences for myself. My assumption is that it's a no-go without major wiring changes in addition to (at the very least) swapping out the instrument cluster.

Anyone have any insight on this? It's more idle curiosity right now than anything else, but I'd be interested to see if it has the potential to go somewhere.
 
:thumbup:
 
The ECU might (probably would) get REALLY angry about not being able to talk to the TCU - unless the later TJs used the AW-4 and you can grab the matching TCU as well? I don't know much about TJs. You could also pull the ECU out of a manual TJ so that it won't even be looking for comms with the TCU, then your TCU AFAIK will go about its business working properly and may try to throw an error code but it can't since it won't be able to report to the ECU. You're also likely correct about the instrument cluster since it's on the CCD bus on 97+ XJs.

TJs are really rare in the junkyard I go to, so I haven't dug into one yet. Usually they only have a few rusty, really picked over YJs.
 
The ECU might (probably would) get REALLY angry about not being able to talk to the TCU - unless the later TJs used the AW-4 and you can grab the matching TCU as well?

Good point; I'd totally overlooked that. Thanks for the heads-up, and I'll add it to the list. If it ends up having to basically shim between the AW4 controller and TJ ECU, that right there would be a showstopper - my aim is 100% functionality, and I'm not an EE so don't want to get into having to build something to convert AW4 TCU signals to something the TJ ECU can understand.

I don't know much about TJs.

Same here. Been in a bunch, driven a few, and that's about it.

You could also pull the ECU out of a manual TJ so that it won't even be looking for comms with the TCU, then your TCU AFAIK will go about its business working properly and may try to throw an error code but it can't since it won't be able to report to the ECU.

Hm. OK, makes sense. Time to start doing some digging around.

You're also likely correct about the instrument cluster since it's on the CCD bus on 97+ XJs.

Yeah, that's basically the conclusion I'd come to. The instruments are really a lower-down-the-list worry, but they've gotta work at some point.

TJs are really rare in the junkyard I go to, so I haven't dug into one yet. Usually they only have a few rusty, really picked over YJs.

Same here. FWIW, do you happen to know of anywhere that cross-references which busses and ECUs were used in which model years? I'd be especially interested to see what the CRD KJs had in them.
 
Good point; I'd totally overlooked that. Thanks for the heads-up, and I'll add it to the list. If it ends up having to basically shim between the AW4 controller and TJ ECU, that right there would be a showstopper - my aim is 100% functionality, and I'm not an EE so don't want to get into having to build something to convert AW4 TCU signals to something the TJ ECU can understand.
I would suspect you'd be better off grabbing the TJ ECU and faking it out so it thinks it's controlling a transmission (or go with a manual TJ one like I said), then using an XJ TCU and tapping into the TPS signal line and a few others. Converting CCD to CAN bus would be.. interesting. I don't know enough about either of them unfortunately.

Same here. FWIW, do you happen to know of anywhere that cross-references which busses and ECUs were used in which model years? I'd be especially interested to see what the CRD KJs had in them.
Unfortunately, nope. My Jeep knowledge in general is very limited except for XJs (and a bit of ZJ/WJ info mostly pertaining to what can be used on XJs), and even then, I know the most about OBD I and OBD II systems and almost none about Renix.
 
Last edited:
I would suspect you'd be better off grabbing the TJ ECU and faking it out so it thinks it's controlling a transmission (or go with a manual TJ one like I said), then using an XJ TCU and tapping into the TPS signal line and a few others. Converting CCD to CAN bus would be.. interesting. I don't know enough about either of them unfortunately.

Understood, and I'm in the same position re: understanding the busses. This may turn into a learning experience :D

Unfortunately, nope. My Jeep knowledge in general is very limited except for XJs (and a bit of ZJ/WJ info mostly pertaining to what can be used on XJs), and even then, I know the most about OBD I and OBD II systems and almost none about Renix.

No worries, and same again here. I'll keep digging and see if anything turns up.
 
ok, time out, we're getting to in depth about this, esp. for the GPS.

it seems like we need the ECU or other components for the unit to work all the way. seems like the radio and most stuff would work, except the GPS, right? or am I missing something?
 
The TJs never used an AW-4, so wouldn't be expecting anything from a TCU.
I believe the electronic controls for the trans are are built into the TCU on the later TJs.

Here's some information on converting the buss (specifically for the Liberty CRD, but it's similar) http://www.naxja.org/forum/showthread.php?t=955062
 
ok, time out, we're getting to in depth about this, esp. for the GPS.

Ehhh - I disagree on this one. While the idea is to get the GPS working in the factory sat-nav unit as part of this, it appears (at least at this point) that a TJ ECU will be required to make this happen. Rather than figuring out how to piggyback ECUs (which is its own headache, may not even be possible, and adds another layer of complexity and potential point of failure), using the TJ ECU to basically run the XJ and have the GPS work as a side benefit of that makes a lot of sense. The question is whether the benefit outweighs the effort involved; more on that further down.

it seems like we need the ECU or other components for the unit to work all the way. seems like the radio and most stuff would work, except the GPS, right? or am I missing something?

Using what's available from the XJ's bus, the radio will work and the map will display. However, its ability to track your position as you move will be non-functional, so you'll basically have (presumably) a static map of whatever your position was when you powered the unit up. Given what these units are going for on eBay and the forums, that's a lot of money to spend on what's basically a 1.5-DIN AM/FM radio with a fancy display.

tbburg said:
I believe the electronic controls for the trans are are built into the TCU on the later TJs.

Just to clarify the above: did you mean that the electronic controls for the transmission are built into the ECU on the later TJs?

Here's some information on converting the buss (specifically for the Liberty CRD, but it's similar) http://www.naxja.org/forum/showthread.php?t=955062

Hey, you found my favourite thread :) I want to do that same swap at some point, and have been following it to see how it goes for him.

Back to the bus info in that thread, though: it's one of the things that led me to suspect that the ECU approach to making this unit work may not be the best one. I'd like to find pinouts for the head unit if possible to get a feel for what it's trying to read; if it's a question of just feeding it a speed signal (and possibly simulating other expected signals to make it happy), that may be doable with some sort of external box. On a purely practical level, though: for what these things are going for on the secondhand market, the cost of that box plus the OEM head unit may make it financially-prohibitive compared to just going with an aftermarket unit.

Hmmm... This has me wondering how the GPS in the head unit actually works. I don't see why it would necessarily need to tie in to a vehicle sensor in order to figure out position; as long as it sampled your location frequently enough it could just figure out location, bearing, and speed with simple math (which is how most handheld units work). The problem may not be hardware-related, but rather software - something in the head unit ties to the ECU not for getting data that the GPS needs, but for other reasons (head unit anti-theft, controlling other items through the display, etc.). Food for thought.
 
Last edited:
I believe the electronic controls for the trans are are built into the TCU on the later TJs.[/url]
Aw crap, butterfingers. Yeah, that was supposed to read ECU.

:dunce:
 
After doing some poking around over the last few days, it looks (as I suspected) like the effort involved in adapting a TJ ECU to an XJ just isn't worth it on an effort-to-reward basis. It could be done, but it's not going to be a small task - particularly when you start getting into all of the detail items that need to be taken care of. This means that the fringe benefit of being able to run your Mopar sat-nav unit from a TJ in an XJ is basically a no-go, and just grabbing an aftermarket unit would be a better bet.
 
Back
Top