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Many UrS-cars came from the factory equipped with a ZF steering rack with speed-variable assist. This system is called "Servotronic". The intent was to provide significant steering assist, aka "power steering" at low speeds but less and less assist as speeds increased. The amount of the assist is controlled by the Servotronic Control Module. Some people don't like it and disconnect Servontronic, either at the steering rack connector or by removing the relay. The connector location is as shown below.
Here is a Servotronic steering rack out of the car, showing the location of the connector (the black one) near where the steering column attaches to the rack:
There are at least two kinds of Servotronic control modules depending on the year of your UrS.
The 92 and 93 spec UrS4s have their Servotronic control modules located behind the dash above the glove compartment (the green module in the photo below). The PN for this module is 44397307B for the 92 and 93 spec UrS4s as shown in the photo, up to VIN PN 150000 (the end of the 93 MY run). To disable Servotronic on these cars, it is easiest to just disconnect the plug at the steering rack (location shown above).
Here is a close-up of the green contol module:
Base Photo courtesy of "ringbearer" (Dan T)
With the 94 UrS4 (VIN RN 000001 and above) and the 95 to 97 UrS6s, the Servotronic relay (PN 4A0907307B) was moved to Position 16 in the Auxiliary relay panel No.1, the black plastic "lunch box" under the hood. It is the "362" module shown in the diagram and photo:
Here is a close-up of the "362" control module:
Base photo courtesy of AudDudi.
My 98 C4 A6 V6 avant has Servotronic. The relay is in the same position as the UrS's "362" except it is labeled "357" on top and the PN is 4A0907307A as per the diagram above. Looks very much like the "605" in the photo below. The 4A0907307A is also the PN for the 94 spec C4 100 (and the 95-97 C4 A6 V6 cars). Here is what the "357" looks like inside (presumably all the others are similar (but subtly different):
Photo courtesy of Brdman.
Several people have found that the later C5 Servotronic Control Modules work in the 94 and newer UrS cars. This includes the 4B0907307 "392" relay that was in the early C5s and the later C5 "605" Servotronic Control Module (PN 4D0907307A). Both are reported to work in the 94 UrS4s and UrS6s to provide less assist at speed. (needs to be confirmed). Apparently later C5 models use the "628" relay (4B007307B) which supposedly provides lower boost. I cannot confirm this. If you can provide any info on the "628" module or a photo (showing the top and front), please chime in.
Photo courtesy of quattron8-JC
This lists shows how widely used the 605 (4D0907307A) module was used (where as the 392 was only used in the early C5 A6s) (both can be found in position 13 of the C5 relay plate):
To add to the "fun" (or confusion) there was also a 4D0907307 "356" control module that was dropped 01/02/2000 in favour of the 4D0907307A "605" module.
Photo provided by Mr.Mojo.
Here is a summary of the Servotronic Control Module part numbers. Now we need feedback on how well the C5 and maybe B7 modules work in our UrS-cars.
Thanks to John C (quattron8-JC) for starting this table and getting me to check and complete it.
More info about the C4 underhood relay and fuse box
Hope this helps someone.
Thanks to those who posted the photos and diagrams used in this post.
Here is a Servotronic steering rack out of the car, showing the location of the connector (the black one) near where the steering column attaches to the rack:
There are at least two kinds of Servotronic control modules depending on the year of your UrS.
The 92 and 93 spec UrS4s have their Servotronic control modules located behind the dash above the glove compartment (the green module in the photo below). The PN for this module is 44397307B for the 92 and 93 spec UrS4s as shown in the photo, up to VIN PN 150000 (the end of the 93 MY run). To disable Servotronic on these cars, it is easiest to just disconnect the plug at the steering rack (location shown above).
Here is a close-up of the green contol module:
Base Photo courtesy of "ringbearer" (Dan T)
With the 94 UrS4 (VIN RN 000001 and above) and the 95 to 97 UrS6s, the Servotronic relay (PN 4A0907307B) was moved to Position 16 in the Auxiliary relay panel No.1, the black plastic "lunch box" under the hood. It is the "362" module shown in the diagram and photo:
Here is a close-up of the "362" control module:
Base photo courtesy of AudDudi.
My 98 C4 A6 V6 avant has Servotronic. The relay is in the same position as the UrS's "362" except it is labeled "357" on top and the PN is 4A0907307A as per the diagram above. Looks very much like the "605" in the photo below. The 4A0907307A is also the PN for the 94 spec C4 100 (and the 95-97 C4 A6 V6 cars). Here is what the "357" looks like inside (presumably all the others are similar (but subtly different):
Photo courtesy of Brdman.
Several people have found that the later C5 Servotronic Control Modules work in the 94 and newer UrS cars. This includes the 4B0907307 "392" relay that was in the early C5s and the later C5 "605" Servotronic Control Module (PN 4D0907307A). Both are reported to work in the 94 UrS4s and UrS6s to provide less assist at speed. (needs to be confirmed). Apparently later C5 models use the "628" relay (4B007307B) which supposedly provides lower boost. I cannot confirm this. If you can provide any info on the "628" module or a photo (showing the top and front), please chime in.
Photo courtesy of quattron8-JC
This lists shows how widely used the 605 (4D0907307A) module was used (where as the 392 was only used in the early C5 A6s) (both can be found in position 13 of the C5 relay plate):
To add to the "fun" (or confusion) there was also a 4D0907307 "356" control module that was dropped 01/02/2000 in favour of the 4D0907307A "605" module.
Photo provided by Mr.Mojo.
Here is a summary of the Servotronic Control Module part numbers. Now we need feedback on how well the C5 and maybe B7 modules work in our UrS-cars.
Thanks to John C (quattron8-JC) for starting this table and getting me to check and complete it.
More info about the C4 underhood relay and fuse box
Hope this helps someone.
Thanks to those who posted the photos and diagrams used in this post.
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