Are all TCUs the same ?

[mozzer]

I need a replacement Transmission Control Unit for my 96 4L Sport, are all the older ones the same or how do I tell the difference in the scrap yard.

[lawsoncl]

Compare the connectors. They should look the same, have the saming keying (plastic ridges) and be the same color. The TCU changed in late 1996 with the switch to ODBII. You could just grab a 92-95 unit and a 1997+ unit and see which one works. Why are you looking for one, btw? It's pretty rare for the unit to go bad.

[mozzer]

I wired in a switch to give the option of locking into second gear when 1st/2nd is selected.

Problem is I didn't put the diode in and accidentally powered up the 2nd gear switch while the TCU was powered up, I guess I should have put a three way switch in so the second gear switch couldn;t be activated with the TCU on.

The light on the TCU switch flickered with the other switch on and now it will only shift from 1st to either 3rd or 4th whichever is selected with the stick.

I know the solenoid works as it will change into second with the new switch.

I don't suppose there are any inline fuses anywhere I could check ???

[lawsoncl]

So it only goes into 1st in (1-2), 3rd in (3), and 4th in (D)? That does sound like a dead or not powered up TCU. I'd check for power at the TCU first. I don't have the wiring schematic handy, but I believe the two power wires are red and yellow (constant power and ignition power). The older XJs had an inline fuse just before the TCU connector. Not sure if an 1996 still has that.

[mozzer]

Actually there must be some power to the TCU because with the selector in D or 3rd it will start off from a standstill in 1st gear, then when it would normally shift into second it will go straight to whichever gear is selected (3rd or 4th).

So there must be power to the TCU but not functioning correctly. Any wiring info would be greatly appreciated.

[lawsoncl]

Ok, so you probably do have power to the TCU. It does seem odd that it's skipping second gear. It would make sense that you damaged the #2 solenoid output if it were skipping 3rd as well. Here's the "map" of how the solenoids control the tranny. You could check the TCU outputs with a meter and see what is really happening. But, yeah swapping the TCU would be an easy check too.


http://www.greatlakesxj.com/tech/TCU5.jpg

[mozzer]

Swapped the TCU and no difference, 1st gear selects automatically then skips to 3rd or 4th whichever is selected on the shifter.

I could understand it if one solenoid was not working or something but if I power up solenoid No.2 it will go into 2nd when in 1st/2nd position so the solenoid must be functioning.

I am lost now, do you have a circuit diagram at all ??

[mozzer]

As it says really as I don;t know where to look now. :dunno: