1997 Jaguar XJR transmission disengages briefly at highway

MICKAEL7

MEMBER
1997 JAGUAR XJR
6 CYL
2WD
AUTOMATIC
14,000 MILES

I have a 97 jaguar, xjr with inline supercharged 6 cyl engine and the GM transmission (L480E I think is its model). The trans fluid is in excellent shape and recently changed. No problems with it shifting at all. But, this has happened twice now, at 70-75mph, (2200rpm) the engine suddenly overrevs and climbs to about 3000 -3200 rpm for 3-4 secs and the speed drops off. It feels like the transmission has simply disengaged itself for no apparent reason. Fluid level is slightly above the add mark on the dipstick (probably 1/3 pint overfill) and I am getting no engine codes. I am thinking shift positon sensor in the trans or prndl switch or traction control failure. But this is just a semi educated guess as I have only owned the car for a few months and have not a lot of knowledge on it yet. Is this a common problem? Any suggestions?
thanks
mick

1 Reply

KHLOW2008

MECHANIC
41,815 POSTS

Hi Mick,

Thank you for the donation.

Overfilling of trans fluid can cause the symptoms described. Recheck the trans fluid level again if you did not follow the following procedures.

Hydra-Matic 4L80-E & ZF 4HP 24E

1. Park vehicle on level ground. Apply parking brake, and run engine at 750 RPM for several minutes. Shift gear selector through all ranges and return to Park.

2. With engine idling, withdraw and wipe dipstick. Replace dipstick in filler tube, withdraw again and check fluid level. Fluid level should be between MAX and MIN marks on dipstick. Add fluid if necessary. DO NOT overfill.

NOTE: Transmission fluid temperature MUST NOT exceed 122 °F (50 °C) when checking fluid level on ZF 5HP 24 transmission.