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Jaguar XJ-S Service Interval Counter

Jaguar XJ-S

Oxygen Sensor Service Interval Counter

The idiot light came on on the dash of your early 80's XJ-S, so you installed new oxygen sensors like a good little boy.  Then you were irritated that the light was still on.  Sorry, the light couldn't care less about whether your sensors were new, old, or even exist; it is controlled by a service interval counter in the trunk.  It simply counts the miles you've driven since the last time the counter was reset, and once 30,000 miles are up, turns on the light.  You now need to reset the counter to turn the light off.

So, the next question is: where is that counter again?  It's in the trunk, near the filler cap.  You need to remove a section of carpeted panel in the front left corner of the trunk to see it.

The next question after that:  how do you reset it?  Well, you need to push the button.  This picture should help:

This view is from inside the trunk, over against the inside of the left fender, backed up against the left rear taillight housing.  It's easy enough to hold a camera in this position to get the pic, but the only way you're gonna get in there to see this view is by popping an eyeball out and holding it in there!  Still, the pic should help you figure out when you've found the right thing.

Note that the button that needs pushing is just the center of that white tit.  The white ring around it won't move.  You will need a pointy object, like a toothpick, to push the center button in.  It moves inward about a half inch; make sure it is securely pushed and held a second before releasing; you want the counter reset all the way, not part way.

For your further edification, here are some pix of the service interval counter removed from the car:

Note that it is not recommended that you remove it from the car!  The two screws that hold it have nuts on the back side, and it is really frustrating to try to hold the upper forward one in place while trying to get the screw started.  A piece of masking tape helps.

How about that threaded boss on the front side, huh?  It's clearly a formed attachment for a speedometer cable, but as the early 80's XJ-S has an electronic speedometer it's pretty pointless.  It would have to be drilled out to use.  Clearly, they wanted to use the same plastic housing for either electronic or cable-driven units.

While resetting this service interval counter is easy enough once you know how, others have suggested that it merely be removed and tossed.  It was originally installed because the EPA requires emission control systems to work for 50,000 miles but the oxygen sensors were only good for 30,000 miles, so the owner had to be gently reminded to replace them.  Once you're past 50,000 miles -- as one would presume most early 80's cars are -- you're legally on your own here.  Of course, it does make a handy reminder that it's time to replace the oxygen sensors -- or anything else you feel should be done every 30,000 miles, like maybe grease the chassis.

Note that the 70's XJ-S also had a service interval counter, but it was cable-driven and located under the dash somewhere.  It also had nothing to do with oxygen sensors, since those cars didn't have any.  Late 80's cars reportedly had no service interval counters, and 90's cars gradually adopted OBD and OBD II features where the ECU would actually detect malfunctioning parts such as oxygen sensors and give the driver a real fault code.


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