If you would like to change axle ration on your 2.7 CRD Jeep Grand Cherokee, then transmission will go into Limp Mode. It is because transmission does not have output speed sensors and speed is taken from ABS sensors. Due to axle ratio change there will be mismatch with transmission input and output speed. Because of this car will go into Limp Mode and transmission will show fault P2502, Chrysler ID 51 Transmission slipping / Incorrect Axle Ratio.
To avoid such problem we made CAN bus filter. It will filter CAN bus speed data from ABS and replace it with current axle ratio data. With using such filter you can make any axle swap. Front and rear axles must be always with the same ratio.
Please note that this filter is only compatible with 2.7 CRD models of Jeep Grand Cherokee. Gasoline models of Grand Cherokee have output speed sensor in Transmission and they do not need any filter for axle swap.
Our CAN filter is configured to work with major available axle ratios, but we can program it to work with any axle ratio if requested. Axle ratios can be switched easily by user from settings switch and current preprogrammed ratios are: 1:3.08, 1:3.55, 1:3.73, 1:3.91, 1:4.10, 1:4.56, and 1:5.13

Installing CAN filter takes about 1-2 hours and it requires some electrical skills. So do not try to install filter yourself and find electrican if you do not know how to find correct wires or how to use soldering iron.

First you must open filter box and switch settings for your axle ratio. On next photo you can see filter board and switch where you can choose correct axle ratio. On back side of the board there are marked switch settings:

Axle RatioSwitch ONSwitch OFF 
3.0812, 3CAN bus filter for Jeep WJ 2.7 CRD Axle ratio change
3.55-1, 2, 3
3.7321, 3
3.911, 23
4.1031, 2
4.561, 32
4.882, 31
5.131, 2, 3-
Switch 4 is reserve for future use and does not affect anything.
CAN bus filter Jeep WJ 2.7 CRD axle ratio change switch settingsOn back side of the filter are marked switch settings.

For assembling first disconnect battery, it is important!

jeep 2.7 axle ratio replace can bus filter diagramHere is a diagram of original CAN bus wiring and wiring with axle mount filter with all necessary wire colors and connection points.
Wire colors are:
DG/WT Dark Green with White stripe
LG/WT Light Green with White stripe
OR/DB Orange with Dark Blue stripe
WT White

Filter should be placed inside the car, on top of driver’s legs, you should take cover off to get place. There is enough space and finding good place is not hard. Check at next image how we placed filter on our test car.Jeep 2.7 crd axle ratio swap filter installation
Junction Block Jeep WJ ABS axle ratio change filter power pinRed wire is +12 volts and should be connected to +12v RUN/START, for example to the Junction Block plug C2 pin 11 wire. This wire is orange with dark blue stripe.
Black cable is ground and needs to be connected to the car chassis.
All 4 CAN wires of the CAN bus filter must go into engine bay through existing rubber grommet.Jeep Grand Cherokee WJ WK engine bay rubber grommet wiring hole
Jeep Grand Cherokee 2.7 crd axle ratio replace abs can bus filter connectionIn engine bay you should disconnect and take out ECM (2x 10mm bolts) to get more space. There are a lot of cables coming from ABS module, you need to find CAN bus cables for connecting the filter. Can cables are a twisted pair (2 wires) and you should cut them about 7…10 cm from ABS plug.
ABS CAN L cable is dark green / yellow stripe
ABS CAN H cable is light green / white stripe
CAN filter cables must be soldered:
Filter violet: ABS side dark green / yellow stripe
Filter yellow: ABS side light green / white stripe
Filter green: car side dark green / yellow stripe
Filter brown: car side light green / white stripe

Isolate all connections and wires, place ECM back, connect battery and you are ready to go.

Axle swap does not affect car speedometer. Axle swap filter is modifying CAN bus signals, but speedometer gets speed signal from ABS through J1850 bus and it will remain as before. Speedometer will be affected if you replace stock tyre size, for example with bigger ones. In such case you can correct it with our JeepDiag Pro diagnostic app. In spring 2018 we will add option for speedometer correction with any tire size into JeepDiag.