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Trying my worst to install an OHC in my 97 but computer just won't give valid reading

Patriotsix

NAXJA Forum User
My OHC computer comes on when it's all wired up (97 XJ with a 97 OHC and harness) but it only gives --- for the odometer etc. No actual reading for any thing. My 97 didn't come with an OHC so I ordered this one. The computer had a small burn spot on the bottom left of its screen so I told the guy and he sent me a free replacement, the replacement has the same spot but I tried it any way and it does the same thing. I don't know what to try next. I get --- on every reading it puts out and it also turns off with my headlights? I'd love to have one of these OHCs but I'm this close to ditching the whole project. Can I order a new computer for it any where? Not used?
 
I am putting a '99 overhead in my '00. My knowledge is limited but I have poked around to lay some ground work for when I do the job in the spring. Best I can tell from my research is that these are the functions that an XJ overhead offers:

Outside temp
compass
average mpg
instant mpg
distance to empty
elapsed trip time

So when you say only gives --- for the odometer I wonder what odometer. Did you try a reset? I would try to see what's what before I buy a new computer. Figure about $250 for one. They are out there. The part for my '00 is 56009380AB. Don't see why a '97 would be different but then again who knows.
 
The XJ 97-01 OHC is plug and play, any 97-01 OHC will function in any 97-01 XJ, OHC from other models are not plug and play. If a 97-01 XJ OHC is not displaying correctly the electronics in the console are toast, or the wire harness is damaged.
 
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so my findings with some tests on a grand cherokee ohc is it will not work unless its getting data from the ecu over the ccd bus. it will be 2 wires twisted together. my grand cherokee computer wont even give the compass function with out a valid speed over the ccd.

so it sounds like your lacking data from the ecu.

also the little burn on the bottom of the screens are from manufacturing all vacuum florescent displays seem to have them.
 
so my findings with some tests on a grand cherokee ohc is it will not work unless its getting data from the ecu over the ccd bus. it will be 2 wires twisted together. my grand cherokee computer wont even give the compass function with out a valid speed over the ccd.

so it sounds like your lacking data from the ecu.

also the little burn on the bottom of the screens are from manufacturing all vacuum florescent displays seem to have them.

Could very well be the harness then, could explain why it goes off with headlights
 
ok lets check some wires to see if the voltage is right and there.

on the black 12 pin compass connector
pin 1 is black and ground
pin 2 is pink and constant 12v
pin 4 is violet with light green ambient temp signal
pin 5 violet with brown CCD bus +
pin 6 is white with black and a switched 12v in run/start
pin 7 yellow 12v with doors open
pin 10 is black with light blue ambient temp ground
pin 11 is white with black CCD bus -
pin 12 is black light green ground

pins 5 and 11 should have there wires twisted along there run as it is serial data
pins 4 and 10 are from the ambient temperature sensor and can be checked with an ohm meter. SENSOR TEST
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Unplug the temperature sensor wire harness connector.
(2) Measure the resistance of the temperature sensor. At -40° C (-40° F), the sensor resistance is 336
kilohms. At 55° C (131° F), the sensor resistance is
2.986 kilohms. The sensor resistance should read
between these two values. If OK, go to the Sensor
Circuit Test. If not OK, replace the faulty sensor

if you can confirm that the wiring is working the only 2 things left are no ccd bus data or a bad compass module.
 
I am really curious if the engine runs well. Even if it is 4 years old. I am curious how the problem was fixed.
 
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