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I just got the 2008 service manual on CD and have been piecing together the differences between the FDI and FDII. If you really need the off-road capability, it seems the FDII is worth the extra money. From the brake lock differential description, the FDI essentially has electronic locking diffs that are always on regardless of ESP or 4x4 settings. The FDII has an additional low speed off-road program when switched to off-road mode. The anti-lock braking also works differently between the two models. The FDII is also sealed for water fording.
 
I've recently tried my FDI euro pat's TCS. One wheel was in the air and the other (right front) was stuck in a hole. As I revved the engine up both wheels began to spin, I've noticed ESP icon blinking and my pat has passed through.

I've also tried to partially disable ESP by pushing ESP Off button once. This also disables TCS: wheels were spinning freely and pat was not moving.

Also engaging 4WD Lock didn't help to move with ESP partially disabled.
 

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I've recently tried my FDI euro pat's TCS. One wheel was in the air and the other (right front) was stuck in a hole. As I revved the engine up both wheels began to spin, I've noticed ESP icon blinking and my pat has passed through.

I've also tried to partially disable ESP by pushing ESP Off button once. This also disables TCS: wheels were spinning freely and pat was not moving.

Also engaging 4WD Lock didn't help to move with ESP partially disabled.
Thats exactly what i was hopeing to hear. Thanks for the real world information. :smiley_thumbs_up:
 
Thanks, sgsgsg. That's interesting and contrary to what my owner's manual says. It says brake TC is always on, regardless of ESP enabled/disabled state. Partial off just disables engine torque reduced TC, according to my owners manual.
 
Thanks, sgsgsg. That's interesting and contrary to what my owner's manual says. It says brake TC is always on, regardless of ESP enabled/disabled state. Partial off just disables engine torque reduced TC, according to my owners manual.
I'll try it once again next time in order to get some sure.

Could you paste your manual's original text about ESP and TCS?
 
Traction Control System (TCS)
This system monitors the amount of wheel spin of each of the driven wheels. If wheel spin is detected, brake pressure is applied to the slipping wheel(s) and engine power is reduced to provide enhanced acceleration and stability. A feature of the TCS system functions similar to a limited slip differential and controls the wheel spin across a driven axle. If one wheel on a driven axle is spinning faster than the other, the system will apply the brake of the spinning wheel. This will allow more engine torque to be applied to the wheel that is not spinning. This feature remains active even if TCS and ESP are in
either the “Partial Off” or “ESP Off” modes. Refer to “Electronic Stability Program (ESP)” in this Section of this manual.


ESP 2WD Operating Modes
All 2WD vehicles can choose the following ESP operating modes:
ESP ON
This is the normal operating mode for ESP.Whenever the vehicle is started the ESP system will be in this mode. This mode should be used for almost all driving situations. ESP should only be turned to “Partial Off” or “ESP Off” for specific reasons as noted Below.

PARTIAL ESP
This mode is entered by momentarily depressing the “ESP Control Switch”. When in “Partial Off” mode, the TCS portion of ESP, except for the “limited slip” feature described in the TCS section, has been disabled and the “ESP/TCS Indicator Light” will be illuminated. All other stability features of ESP function normally, with the exception of engine power reduction. This mode is intended to be used if the vehicle is in deep snow, sand or gravel conditions and more wheel spin than ESP would normally allow is required to gain traction. To turn ESP on again, momentarily depress the “ESP Control Switch”. This will restore the normal “ESP On” mode of operation.

WARNING!
In the Partial ESP mode, the engine torque reduction and stability features are desensitized. Therefore, the enhanced vehicle stability offered by ESP is unavailable.
NOTE: To improve the vehicle’s traction when driving with snow chains, or starting off in deep snow, sand or gravel, it may be desirable to switch to the “Partial Off” mode by pressing the ESP switch. Once the situation requiring ESP to be switched to the “Partial Off” mode is overcome, turn ESP back on by momentarily depressing the “ESP Control Switch”. This may be done while the vehicle is in motion.

ESP 4WD Operating Modes
In addition to ESP ON and Partial ESP (described above in “ESP 2WD Operating Modes”), all 4WD equipped vehicles can also choose the following ESP operating mode:
ESP OFF
This mode is intended for off-highway or off-road use when ESP stability features could inhibit vehicle maneuverability due to trail conditions. This mode is entered by depressing and holding the “ESP Control Switch” for 5 seconds when the vehicle is stopped and the engine is running. After 5 seconds, the “ESP/TCS Indicator Light” will illuminate and the “ESP Off” message will appear in the odometer. Press and release the trip odometer button located on the instrument cluster to clear this message.In this mode, ESP and ECS, except for the “limited slip” feature described in the TCS section, are turned off until the vehicle reaches a speed of 35 mph (56 km/h). At 35 mph (56 km/h) the normal ESP stability function returns with the exception of engine power reduction. TCS remains off. When the vehicle speed drops below 30 mph (48 km/h) the ESP system shuts off. ESP is off at low vehicle speeds so that it will not interfere with off-road driving but ESP function returns to provide the stability feature at speeds above 35 mph (56 km/h). The “ESP/TCS Indicator Light” will always be illuminated when ESP is off.
 
It may be a difference between the exported models - PolishedHeckler had posted an experience with right front and left wheels in the air and still regained traction - per the owner and service manuals. My experience in the snow last winter was stellar (did not even engage 4x4 lever) - much better than my '94 Grand Cherokee 4x4 (10 years experience - also great vehicle).
 
The 2008 service manual does describe a difference with the brake lock differential programming for the FDII in off-road low speed mode - maybe the FDI is not programmed to handle the tires in the air as the FDII is able. Maybe yet another reason to spend the extra dollars on the FDII.
 
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