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As I mentioned, I finally got my 95 XJR running, after 4 years, due to a sheared woodruff key, ( go figure ) anyway the tach stopped working within a few minutes of starting. It still starts and runs fine, just no tach, I know it is not the cps, as it still starts and runs ( and I replaced it, with same results ) I also swapped out the ecu as I have a spare ( also no difference ) so does anyone know where and how the tach gets its signal from. The car drives fine but it trips the transmission light, and throws codes
P1775 (general transmission fault ) and
P0726 ( engine speed input circuit range/performance ) and
P0727 ( engine speed input circuit no signal ) as from what I have read on this forum the trans light and code 1775 for the trans would be expected as the trans says its turning, but it is not matching the engine rpm, as it is not getting the signal that the engine is turning. So the tach must get its signal from somewhere other than the cps. I have been searching the forums for answers. I even have the useless disc from JTIS but I am not able to find anything usefull at all.
Any ideas, if its just a bad tach that would be good, but I find it hard to beleive that the transmission gets it engine speed signal from the tach
It ain't so simple- The "tach" is an electronic function that is absolutely DERIVED from the CKPS, (not the CPS). Obviously your CKPS is working or the car wouldn't run. I am not at my computer with the diagrams, but I am pretty sure the ECU, which gets the CKPS signal, sends the derived speed to the instrument module and the transmission module over a network connection. As I said, I don't know the exact connection on an X-300 but I will look it up in a day or two for you if someone else doesn't chime in before then. In the mean time, i would look for loose plugs on the TCU and the instrument module.
MY 89 V12 convertible
MY 99 XJR
MY 02 XJ8
MY 12 XF R
I just came across this same issue this morning! As I'm heading to work, I noticed that my fuel gauge was on Empty (which I definitely didn't leave it at), and my gauge for coolant temp was all the way down (assuming the car still needs to warm up). So i'm driving to the gas station when I notice that none of the needles are moving on the Tachometer or other gauges. I was hoping to see that this is a simple fuse type of situation, but i'm not to savvy on cars when it comes to the electrical lingo. If I could get a hand from anyone it would be appreciated!
In my post when I said cps, I ment the crank position senser, that is what I replaced, and as you noted it starts and runs fine so it has to be working. I will continue checking conections for trans and such.
It did the car no favors sitting for that long, it had a bunch of issues the first couple of days, ( traction, abs, etc ) but all that seems to be left is the non working tach and trans light.
I really appreciate everybodys help
I was wondering if you found those link connections for the tach, I did check all the transmissions connections, the 3 at the tranny and the TCU. It is still running good, just no tach and I have noticed that the fuel gauge every once in a while wobbles a little bit, I would think that it is just a instrament pack issue except for the fact that it trips the trans light and and throws the code for no engine speed signal, and like I said before I cannot beleive that the trans TCU gets its engine speed signal from the inst pack but I guess it is possible,
Any ideas anyone ?