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Does anybody know of a place to buy a code reader for the XJ40 series XJ6, please? It would be an OBDI scanner but I think the connector is custom Jaguar - maybe the protocol is, too? There has to be some entrepreneur who has modified off the shelf code readers? Thanks 1994 XJ6
AFAIK the thing you are looking for does not exist - and why bother? The Xj40 has a built-in code reader on the dash - isn't that enough?
Do you feel you need a more granular view of the issues with the car? Just wondering, what issues have presented themselves that you feel you need an auxiliary code reader?
Most problems can be analyzed from the code displayed when the check engine light illuminates.
One forum member, Nick, has a Jaguar PDU unit that plugs into the socket under the battery support, but It's hardly what you'd call portable - and working units are very rare.
AFAIK the thing you are looking for does not exist - and why bother? The Xj40 has a built-in code reader on the dash - isn't that enough?
Do you feel you need a more granular view of the issues with the car? Just wondering, what issues have presented themselves that you feel you need an auxiliary code reader?
Most problems can be analyzed from the code displayed when the check engine light illuminates.
One forum member, Nick, has a Jaguar PDU unit that plugs into the socket under the battery support, but It's hardly what you'd call portable - and working units are very rare.
Larry
It is just insurance policy. I do not believe the dash will show more than the first code, right? It is often useful to triangulate from multiple codes. It was worth a try asking. Regards, Bo
I do not believe the dash will show more than the first code, right?
Hi Bo,
The VCM will display all of the ECM diagnostic trouble codes, but you have to delete them one at a time in order to see them all. To do that, you pull a fuse in the center console fuse box. Off the top of my head, in the '93-'94 cars I think it is fuse #9, or the second fuse from the left. Be sure to write down each DTC exactly as it appears before deleting it.
do you really think the VCM is enough? Many mechanics have turned me down saying they can´t run a diagnostic..
Eh, seems those mechanics don’t know where the VCM button is. It’s a simple code based diagnostic system, but it pretty much covers all of the inputs into the ECU. Sure, it won’t give you the specific granular information like real-time voltage readings for various sensors, etc, but any halfway decent mechanic can do that with a good DVOM and a test drive.
Diagnosing early GM fuel injected cars is the same thing, it’s no different with our XJ40s. Get the numeric code (count the blinks after shorting the diagnostic connector for GM), look the code up in the book and follow the flowchart. Bingo...
If you think it’s a flakey sensor, bypass it, swap it out, do the wiggle test, and measure resistance and/or voltage through the sensor’s range of motion, temperature, pressure, etc.
The only thing I’ve come across that I’ve “had” to use my PDU for was diagnosing the Bosch transmission ECU. There’s no blink test and the codes don’t appear in the VCM. But even still, you can test likely culprit sensors, switches, and check resistance of solenoids.
And while the Teves anti-skid system doesn’t tie into the VCM either, it has a blink test with many codes, and when that fails, Jaguar has a nice long flowchart so you can manually measure every input and output and find the problem.
Aside from TCM interrogation and a couple neat engine setup procedures (TPS adjustment, idle speed adjustment, idle mixture adjustment, EGR test, kick down switch adjustment), there’s not much else use for the PDU with our 6-cylinder XJ40s. Sure it’s cool, and has way more uses with X300 and newer cars, but the PDU can be cumbersome and slow to set up and operate, especially if you need to use the break out box and cables to interface into harnesses. And mine can be flakey depending on temperature. They were meant to be plugged in and running 24/7 at the dealer, and until I realized that, I had lots of trouble establishing communications with the car until the units were warmed up. (It helped to place them in the sun or the hot car for an hour or two before using them.
It was very handy when setting up the throttle linkage and idle switch on my X300 XJ12, and had many more codes and test options, you could sweep the gauge needles in the cluster, command the climate control flaps to various positions, test the memory seat potentiometers, configure alarm and keyless entry settings... All with one connection to the OBD connector. Everything was networked together. Not so with our XJ40. Special harness adapter for Teves ABS, for Lucas Marelli V12, for Delanair MK IV climate control, etc
I was lucky enough to find mine years ago, randomly, in the For Sale section of a forum which I can't remember. It was something like $350 for the PDU, the base station with faulty Sony-bus CD-ROM drive, a bunch of software CDs, the MPU and its case, two VBA power adapters, a set of voltage probes and replacement tips, the current probe, the self-test lead kit, the VIA module and harness adapters, as well as a few XJ40 development books, the Electrical Guide binder, and the AJ6 Engine Management binder. This was all sitting up in this guy's attic and was sold all together. He also had a new in box additional PDU unit, which I grabbed as well for $75 additional, IIRC. Shipped it all in a nice big plastic crate meant for a Jaguar XF headlamp assembly. Apparently the guy worked at the dealer and pulled all of this out of the dumpster. Since then, I have accumulated 4 or so correct Sony CD-Caddy Drives, and have repaired them with new capacitors, which was the cause of their failure in the first place. It was certainly a score!
Please do as Larry suggests and tell us more about the symptoms and the warning message displayed on your instrument cluster and when you do, I will move your posts to start your own thread on your specific issue.
I have a Check Engine light, the oil pressure light, the light bulb light and the codes the VCM read are: FUSE 1, FUSE 2, PAD... the car runs great to be honest, the other day I tested it at a scenic route. It was awesome ! I really want to repair it... Sometimes it has a misfire, it accelerates a little bit when idle or even when is running... I just ordered a new oil pressure gauge unit which is suppose to replace the old one, from LMD5640AB to JLM20791 and hopefully that will take care of the oil pressure light.. for the Check Engine my mechanic told me to get an "engine rebuild kit" but i don´t seem to find that.... he said he can´t run a diagnostic so he is not sure what to do but with what Nick said I believe is a good idea to understand what the VCM is then, so I don´t have any problems. Any guidance there?
Last edited by lenavarrete; Jul 11, 2020 at 12:45 AM.
You really need to tackle this in a systematic, organized way. You cannot haphazardly start checking and repairing things by just throwing parts at the car. You WILL go broke and grow frustrated long before you get the car running well. Trust me, just about all of us have been there.
First thing first: Replace those bad fuses! You can't fix an issue if circuits aren't getting power...
You have three fuse boxes. One in each front footwell by the door opening, and one inside the center console, under a cover. Take the hour, and pull each and every fuse, one by one, and check them, and clean the contacts. Oxidation will have built up on them in 30 years, and will cause voltage drops in the circuits. Verify the proper amperage ratings while you're in there. Once your lightning bolt (fuse failure) lamp is extinguished, you'll be able to turn the ignition on (engine off), and press the VCM button to get your first Fuel Fail Code. Once you have that number, we can start diagnosing the reason for the Check Engine lamp.
I'm sorry to be so frank, but you need to either find another mechanic, or be willing to research a bit and do some of the diagnostics here yourself... Your mechanic is NOT guiding you in the right direction by telling you to look for an engine rebuild kit... That's ludicrous!
You diagnose the check engine light and drivability issues by following specific test procedures based on the issue the Engine Control Module sees and reports to you through the Fuel Fail Code(s), not by rebuilding the engine.
You are absolutely right, in order to repair things you have to do in order, that makes total sense. Honestly I don´t know what to do so I depend a lot in a mechanic. Most of the time I do read a lot in order to get the right parts for a right fit, but is hard without a proper mechanic. I asked a friend for a recommendation and I found a new mechanic. He just checked the fuses so now I don´t have the FUSE 1, FUSE 2 (three fuses were changed). Now, I only have the PAD at the VCM, but I don´t think I have a Fuel Fail Code and the light bulb light is gone though sometimes it reappears when driving. I will attach a picture. Thank you I actually appreciate when things are told frankly.
Windshield light is on but I literally don´t have a reservoir.
With the Check Engine light lit, you should have a code display - however, it will only display a code if the engine isn't running, in other words, just ign on.
With the Check Engine light lit, you should have a code display - however, it will only display a code if the engine isn't running, in other words, just ign on.
Is that how you're checking for a fail code?
Larry
Yes, sorry for the confusion. I do have the engine ON in the previous picture. But I do check the code display while ignition ON, engine OFF. Only PAD appears.
Yes, sorry for the confusion. I do have the engine ON in the previous picture. But I do check the code display while ignition ON, engine OFF. Only PAD appears.
That's weird - I don't think I've heard of that condition before? Try pressing it twice maybe (WAG)
PDU clone? OBD reader
