Resetting the "Check Engine" Light

Last year I learned and applied a trick for re-setting the "Check Engine" light on my 94 Jag XJS. I believe that the procedure was to disconnect one of the battery terminals for at least 30 seconds, or something like that, but I just don't recall exactly. Can someone pease remind me the trick? (Please, no lectures about the need for a qualifed service tech to assess the problem; it was merely the result of low battery power -- happens frequently with a car in storage.) Thanks.

Don't know about Jags. They do have a "few" idiosyncrasies. On many other cars, disconnecting the battery for a couple of minutes will reset the computers, after which they will re-learn the proper behavior. On the other hand, just letting the battery go completely dead would accomplish the same thing. Not much to lose by trying the battery disconnect, unless the Jag happens to require a special dealer only reset.

Good luck,
D

You can either disconnect one side of the battery for 30 seconds, but you will need the radio code to be able to had tunes if you have the stock radio. The other way (the one I use on my '93) is to turn the key on (engine not running) and pull the dash fuse out of the center fuse section (under the arm rest). Watch the gauges, when they drop all the way down you can replace the fuse.
Cheers! /ubbthreads/images/graemlins/thirsty.gif

Thanks for the responses. I traveled to the Jag's storage yesterday and disconnected the negative battery cable for a minute or two, and then reconnected and all was well. Yes, I had to reset the clock and radio code, but the need to reset the Check Engine light has happened enough that I now have the radio code memorized.

It's a Jag thing... as often as the Check Engine light comes on, they should have just put a nice big red reset button next to it. My friends and I chuckle about Jags being the only cars ever made where Check Engine lights ever burn out from being on so much. (Well, actually I don't think it's that funny; I own a Jag remember.)

Thanks again.

The best way to cope with frequent resetting is to turn the ignition but dont start the engine. Open the center console fuse box and find the fuse marked panel instruments and pull the fuse. Wait for the tach and speedometer needles to flick downward about a half a unit, wait a few seconds and replace the fuse. The check engine light should be reset. Much easier than pulling the battery power and easier on the car.

Just a suggestion, but aren't the chances that the "Check Engine" light means you need a new O2 sensor? My '88 doesn't have "Check Engine" it has "Oxygen Sensor" where the "Check Engine" light appears on later models. When mine warning appeared, I simply replaced the O2 sensor and the warning went away -- never to re-appear.

I would think you are curing the symptom of a problem and not the problem.

Webserve

I have had the same problem and I always check the code associated with the 'CHECK ENGINE'The codes for series 4 are as follows 1 mass airflow. 2oxygen sensor.3 running lean. 4 vacume leak.To obtain the codes turn off key for 10 seconds. Then turn on but do not start and the fault codes will be displayed. good luck.

On series 4 XJ6s the codes are far more numerous between 90 and 94. You need a list of them and they can easily be checked with the instrument panel procedure. The codes on 90 through 94 are numbered to forties and are available in most shop manuals. To replace the oxygen sensor every time the check engine light goes on is to have the luck of the Irish and then some. If you think that the series 4 Jags are difficult because of numerous diagnostic faults, you should try the OBD2 system from 95 on. There the codes probably total close to 100. Without this capability, the car would be extremely difficult to diagnose.

I LIVE IN THE TORONTO AREA AND HAVE CONFIRMED THE 1TO 4 CODES I QUOTED WITH MY DEALER THESE CODES ARE APPLICABLE ONLY TO THE CHECK ENGINE WARNING DISPLAYED ON THE COMPUTER SCREEN, IN OTHER WORDS THEY THEY JUST TELL YOU WHAT THE PROBLEM IS RELATED TO THAT ONE WARNING.

Greetings,
The first mistake anyone makes with a Jag is thinking that the dealership knows anything about the car. Period. The 1988 XJ40 may or may not have the 1-4 readings which you describe. It may or may not have a "Check Engine" light. My light says "Oxygen Sensor" and the ONLY thing it monitors is the O2 sensor. There is NO 1-4. Never has been. In 1990 they went into the "FF" codes. The trubleshooting code computers on the earlier XJ40s was so poorly designed that Jaguar gave the order to snip the wires in the back of the dash so the computer could not be connected. Clearly it is a LARGE number of these cars that have this situation for I have run into an equal number that have the code read out and those that do not. One thing I have learned about these cars is that you can have two of them sitting side by side that look identical and you would think they were made in opposite parts of the world.
BTW, the only 420 ever made -- according to my local Jag dealer parts guy -- was made by Mercedes!! He also states that there was never an S-Type made in the 60s -- even though there is a drawing of one in the Sales Manager's office.

Webserve

The frustrating thing about dealers and Jaguar diagnostics is that they are only interested in Jaguars under warranty. This policy is enforced in that the Ford Inc.treats any Jag made before Ford participation as a step child and not worthy of their time. This sadly applies double to the 12 cylinder models. So Corporate backup for diagnostic capability is non existant unless you have one under warranty.

in my 1984 XJ-6 the O2 Sensor light comes on every 45k miles. There is a mechanical counter located in the trunk/boot behind the upholstery panel where the ECU and other electronics are located. This mechanical Counter has a push-to-reset button and that's the end of it. Another 45k miles without the light coming on. Yes, you are supposed to replace the O2 Sensor, but like my local mechanic says, if it ain't broke, don't fix it. translation: if the car is running fine, there's no need to replace the sensor, just reset the counter. It would seem logical to me that the '94 model would have a resetable counter too, but maybe the trick is to erase all codes by disconnecting the battery for a while. Kind of a silly way to reset the light, but by '94 Ford was influencing Jaguar to save a buck here and there, so there you have it, no reset button.