1998 S-reg jaguar XK8 drives perfect until reverse is selected then goes in to reduced performance mode. using a fault code reader fault code P1646 and P0706 were read.

Seems it may be just the transmission cable needs an adjustment, as I find this reference on-line:
p0706 JAGUAR





Jaguar XK8 Technical Service Bulletin S307-01: Selector Lever Cable - Adjustment Procedure - Not In Workshop Manual.pdf Taken from the pdf material: After replacing the selector lever
cable or repairing a fault concerning range selection, such as DTC
P0706 - Transmission Range Sensor Circuit, Range/Performance, the
selector lever cable needs to be adjusted according to the procedure in
this bulletin.
The cable is adjusted by moving the locknuts that secure the cable
sheath to the J-gate assembly. This movement will lengthen or shorten
the effective length of the cable sheath between the Jgate and the
anchorages of the cable sheath.
Procedures covered: Adjusting of Transmission Selector Cable
(including Cable Sheath Locknuts diagram & Transmission Lever
diagram) of Jaguar XK series vehicle.
This manual is available FREE at European Transmissions website The manuals state P1646 is ECM HO2S control malfunction ?
Engine A bank heated O2 sensor which is upstream. It can be triggered when the
Ignition ON > 8 seconds, When CK ENG MIL is activated
(DTC flagged; second trip), ECM:
? Inhibits A bank upstream HO2S
operation. Can be caused by these:
HO2S heater failure,
HO2S sensing circuit short circuit to
ground or high voltage,
HO2S sensing circuit open circuit,
ECM failure
I don't see any codes for P0706...but there is on-line this reference: I'd go to this site and read the info...http://www.europeantransmissions.com/Bul... Best regards, Michael Seems it may be just the transmission cable needs an adjustment, as I find this reference on-line: p0706 JAGUAR Jaguar XK8 Technical Service Bulletin S307-01: Selector Lever Cable - Adjustment Procedure - Not In Workshop Manual.pdf Taken from the pdf material: After replacing the selector lever cable or repairing a fault concerning range selection, such as DTC P0706 - Transmission Range Sensor Circuit, Range/Performance, the selector lever cable needs to be adjusted according to the procedure in this bulletin. The cable is adjusted by moving the locknuts that secure the cable sheath to the J-gate assembly. This movement will lengthen or shorten the effective length of the cable sheath between the Jgate and the anchorages of the cable sheath. Procedures covered: Adjusting of Transmission Selector Cable (including Cable Sheath Locknuts diagram & Transmission Lever diagram) of Jaguar XK series vehicle. This manual is available FREE at European Transmissions website The manuals state P1646 is ECM HO2S control malfunction ? Engine A bank heated O2 sensor which is upstream. It can be triggered when the Ignition ON > 8 seconds, When CK ENG MIL is activated (DTC flagged; second trip), ECM: ? Inhibits A bank upstream HO2S operation. Can be caused by these: HO2S heater failure, HO2S sensing circuit short circuit to ground or high voltage, HO2S sensing circuit open circuit, ECM failure I don't see any codes for P0706...but there is on-line this reference: I'd go to this site and read the info... http://www.europeantransmissions.com/Bulletin/DTC-jag/Jag/307-01.pdf Best regards, Michael