• 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.

Recalibrating 97+ Digital Odometers (electrical engineers)

chief xj

NAXJA Forum User
Location
PA
Hi all, I recently scored a 98.5-2001 Police Package Gauge Cluster that came out of a 98 police jeep. The only problem (obviously) is that the odometer reading is incorrect. My 99 XJ currently has 115K on the odo, but the police odo has 88K on it. This question has come up here before, and like always, the answer is either to take it to a speedo shop and bend over, or deal with the different mileage. I need some help from the electrical engineers out there to figure a way to recalibrate it. I know it can be done, but it appears to be complicated. I tore the cluster apart down to the two circuit boards. This is what I found out.

There are 11 basic IC’s on the main board (see picture). There is one oscillator on the board and it reads 4.00000. So I assume that is a 4.0Mhz clock oscillator, meaning that all data entry into the ICs are synchronous. It appears that all chips are CMOS chips. I am almost 100% sure that IC’s 1,2, 10, and 11 are stepper motor drivers, and have no effect on the odometer reading. IC5 is a buffer, and IC6 is a Schmidt trigger. IC9 is a quad NOR gate. I have no clue what IC7 is, I couldn’t reference it on the net. It’s a Philips 4632650-1. I couldn’t find anything on IC8 either. Its an IC specifically engineered for Chrysler. It reads 94Chrysler, SC427292CFN. I’m guessing that it is the IC that allows the gauges to do their self-test. But I am aware that the cluster also times the rear defrost cycle, so maybe it has something to do with that.

Now on to IC’s 3&4. They are both 8-bit shift & latch registers. I believe this is where the odometer, and trip odometer readings may be kept. But im not sure which IC controls the trip and reg odo. Unfortunately these two IC’s are surface mount. Damnit! So could this just be a matter of clocking the chip, enabling it, and shifting in the correct odo reading?

There is another possibility. The secondary board consist of the display, one big 42 pin IC, the reset switch for the trip odo, and a couple of current limiting resistors. I can’t read what’s printed on the 42 pin IC, the display is basically sitting on top of it. I believe this IC drives the 6 7-Segment displays and is also a counter. However, they may be some chance that this 42-pin IC holds the odometer reading. If this is true, then all you have to do is remove it from the old cluster and insert into the new one. It seems to be to easy though.

Guys, I need all the help I can get here. I am basically flying blind because I have no schematics for anything. If anybody can help out, please chime in. Sorry for a very lengthy post.

Brandon

Pic1: Main PCB

1.jpg


Pic2: Secondary PCB

2.jpg
 
IC7 is probably memory, and IC8 is probably a processor.

The ECU would likely communicate with the Guage Cluster processor using some sort of protocol--which is why it displays a 'bus error' when there is a communication problem. Chances are that it is not as simple as 'clocking-in' odometer/speedometer clicks.

Try to find a schematic. See if the speed sensor feeds directly, and only into the ECU. If so, OBD is probably your easiest method. Make a friend with a box.
 
Have you tried installing it yet? If its the same as other chrysler products, the milage should be stored in what the dealer called the "body control module". Had to install a used cluster in a Dodge Stratus in the past, and when we first started it afterwards it changed to the correct milage after running for a minute or two...
 
I'm having a tough time finding a schematic or just general information on this particular cluster. I’m not sure if OBD is the easiest method. I would prefer just to work directly with the chip. bfred, for some reason, the XJ was probably the only Chrysler model to not use a BCU. Therefore, the odometer reading is kept in two places: in the ECU, and on one of the cluster chips. Had DC used a BCU or fed the odometer directly from the ECU, we would not be having this conversation. Thanks

Brandon
 
Pull the VSS out of the TC, put in a drill chuck, and let'er run!?

p.s.
IC7 may be a CANBus transceiver.
 
Last edited:
Do what I did when I did my 98, make a note in the back of the owners manual and use the gauge clusters milage when you renew your registration. Milage is stored two places, cluster and ecu and they don't interact in milage.
 
Well I had thought about that. Then I though why not hook a function generator up to it. You could vary the frequency of the generator to the point where you could simulate very high speed and vary the odometer in a short time.

Brandon
 
Indicated mileage only matters when you are trying to sell it; you can note the correction at that time if you want...88,000 miles is nearly enough to scare most non-Cherokee owners away anyhow.
 
It can be changed if you can write a program to do it. A DBRIII Scan Tool with the Chrysler software will do it. So I know it can be done. Why don't you just take it to the service center tell them you had to replace the insterment cluster, and you need them to recalibrate the mileage. I doubt you'll get much static sense you need the odo mileage raised.
 
Yucca-Man said:
Indicated mileage only matters when you are trying to sell it; you can note the correction at that time if you want...88,000 miles is nearly enough to scare most non-Cherokee owners away anyhow.

That's so sad considering what a baby it is at that age most likely and can probably go to 300K miles. :laugh3:
 
Just a quick update. I took the display board out of my original cluster and put it in the police cluster to see if the mileage would be correct, and unfortunately it changed to what the police cluster is. So with that said the odometer reading is definitely kept on one of the IC's on the main board. I guess my next step would be to disconnect the VSS and find a way to get it spinning fast. I think Ill try the function generator first. Does anybody know what kind of wave the VSS sends the computer? Is it a sine wave or is it a pulse? Thanks.

Brandon
 
I'm not sure how set you are on doing this yourself, but I believe the mileage is store on one of the ICs...probably flash memory of some sort.

Here in Cali, you can pay people who have the right gagets to reprogram a digital speedometer.

That's what I had done when I replaced my dummy cluster ('00) with one from a police package. It cost about $100 and takes about 30 minutes.

You might try a google search for your area...I remember someone mentioned on this forum that the dealer could reprogram those speedometers...
 
IC13 is the correct chip, 93c56. It is a three wire Microwave EEPROM. It contains the VIN and odometer reading, both repeated three times for redundancy. The nice part about it containing the VIN is that it can be detected if the cluster has ever been swapped.

Here is the issue, I can read the EEPROMs on both of my clusters, but using PonyProg it always fails to write. Any insight as to why?
 
IC13 is the correct chip, 93c56. It is a three wire Microwave EEPROM. It contains the VIN and odometer reading, both repeated three times for redundancy. The nice part about it containing the VIN is that it can be detected if the cluster has ever been swapped.

Here is the issue, I can read the EEPROMs on both of my clusters, but using PonyProg it always fails to write. Any insight as to why?

I believe the issue is that PonyProg does low layer COM port manipulation which my Prolific based USB -> Serial adapter does not support. I am going to buy a FTDI based cable and see if that fixes the issue.
 
You do realize you bumped a nearly 6 year old thread?
 
Reprogrammed a dumb cluster to 98 miles.

gallery_1_12_154823.jpg


Then I found out the hard way that my new programmer is incompatible with Fairchild 93C56 chips in 1999-2001 clusters. Everything still works, but it no longer stores mileage. Oh well, I have chips and a new new programmer on the way.

gallery_1_12_146262.jpg
 
Nifty. Thanks for posting this.

I was going to say there was a chance the hardware write protect pin was enabled, but it appears you've gotten writes working, so that can't be correct.
 
This is great, keep plugging at it.
 
Nifty. Thanks for posting this.

I was going to say there was a chance the hardware write protect pin was enabled, but it appears you've gotten writes working, so that can't be correct.

Yeah, if it was write protected then the cluster could not update the mileage either.

It is just mainly the issue of the capabilities of the programmer. The KMtronic/PonyProg programmer would work if I had a computer with a real serial port. I accidentally bought an older 2009 version of a Willar SP programmer.(It was cheap!) Once I get the Fairchild compatible version I will post a tutorial.
 
Back
Top