Hi All,

Great Forum, very informative well done to one & all!!

To cut a long story short, I've owned my 99 XJR8 since 2002. When it came time to PX it for my current Range Rover SC in 2009 I was only offered £1,000 for it. There’s no way I was letting anyone have my pride and joy for give away money so the Jag was moth-balled until a few weeks ago.

Since owning the Jag I've had a reoccurring problem with it going into Engine Fail Safe Mode at random times, with ABS, Stability Control and Trac warnings lighting up the dash. I can't recall the full inventory of works carried out by Jaguar over time, but they could never seem to pinpoint the cause despite changing a number of sensors during the extended warranty period (2005). In the early days the problem occurred so seldom it really wasn't a major issue, just an inconvenience having to pull over turn off the engine and restart again to clear the fault. However, over time the fault occurred much more regularly and did become a cause for concern and eventually decided it was time to move on.

Ok, so the story wasn't that short!

A couple of weeks ago I fitted a new battery and the ole girl fired up on first crank. The fault described above was present immediately and just as before if I turned the engine off, leave for a few seconds and restart the fault clears. But unlike before the fault returns within say a minute. Using an OBD scanner I pulled a number of codes (P1120, P1222, P1364, P1637, & P1642). Using this forums advice I’ve worked my way through each of these and successfully cured all but the P1642 code. I also found the alternator regulator to be faulty so I’ve fitted a complete new alternator.
I’ve read some conflicting information on the possible causes of a P1642 and I’m leaning towards the CAN Bus Failure on or around the ABS control module theory. Before I explore this any further can someone please offer some advice on the following....

1. If I clear the code and disconnect the multi-plug on the ABS module should I expect the same code to be thrown up due to the module not being found by the network, or would this throw a different code and still initiate ‘Engine Fail Safe’ etc..?

2. If pulling the multi-plug clears P1642 can the car be driven safely in this state to see if the P1642 returns on test run?

3. Could the P1642 code be flagged up if the soldered joints on the ABS module PCB are dry? I’ve read much about this problem here but nobody seems to link this issue to a P1642 code.

Thank you in anticipation of any advice.

 

Are you still getting the RP? If not, does the car have any symptoms? If not, then I suspect the P1642 is an artifact of the scanner connection. If you get still RP with no scanner connection, then you are in for a long process of troubleshooting the CAN bus, as you already suspect.

I know of no reason the ABS motor should trigger P1642. It correctly triggers the C code that indicates ABS motor circuit failure. The P1642 indicates a comm failure.

 

Hi Ross,
Thank you for your reply.

I assume by 'RP' you are refering to 'reduced performance'? If so, yes and more than ever before.

RP is initiated within a minute or so of starting the engine, together with ABS, Stability and Trac warnings. This occurs whether or not the OBD Scanner is hooked up and on occassions before the car is driven off.

Your reply suggests I could be barking up the wrong tree with my theory that the problem lies with the ABS module or the CAN Bus network in this area. It looks like I could be in for long haul in tracing this gremlin!

As a matter of interest, is there any such thing as an 'end of line' device which can be introduced to the CAN bus network for testing purposes?

 

Well, the can bus indeed has such a device in its specification, but I am unaware of a diagnostic procedure using the Jaguar's ecu.

I did not mean to imply that the CAN bus at the ABS was not the problem, just that the ABS motor leads were not. In fact, it could be the CAN bus at any of the CAN connected modules, ABS being one of them. motorcarman had a post a whle l back listing the CAN modules. You should probably look at the connectors for each one. I believe the Dealer level software has counters for each module's "lost packets" which might point you in the right direction.

After you reset the codes, does the RP message come on before the CEL, or are they simultaneous? I am trying to help you figure out if the RP is for sure directly connected to the RP code, although it seems like it probably is.

 

P1642 is an artefact of your code reader; ignore.

ABS/Trac errors are almost certainly from your ABS module; resolder the two pins. You can remove the electronic part of the module WITHOUT removing the hydraulics. Undo the module mounts, then lift it up out of the inner wing area, remove the four screws that hold the electronics module in place, and pull it off the hydraulic module. You'll need to bend the brake pipes slightly to get it all the way off; this won't cause permanent damage to them.

I suspect your throttle pot or connections to it are the cause of your failsafe mode; these DO NOT trigger an OBDII trouble code. I've got the same problem at the minute on the SuperV8 and am going to remake the wiring back to the ECU/tighten up the pins in the connector, and attempt to remove/replace the pot on the throttle body to fix it. Will keep you posted.

 

Hi Ross,

Apologies, I may be struggling with some of your acronyms here. CEL = Check Engine Light by any chance? (Referring to ABS, Trac, DSC and warnings).

If I'm correct, then the chain of events are: Red & Amber warning lights illuminate simultaneously, the LED displays ABS, Trac & DSC failures then within a second or two engine goes into RP mode.

The only code logged after this is P1642

 

Chris: you got all of the acronyms so far, so I will just keep using more so you can learn them all!

Marcoscopic: I would generally agree that MOST P-1642 are artifacts as you say- heck I have been the prophet of that for years- check the archives. But Chris is apparently getting the CEL going from off to on without the scanner being connected, then the only code he has when he connects the scanner is the P-1642. That's right, Chris, is it not? If that is the case, since the CEL will not light without a code, then the code was there before the scanner was connected, so it would therefore NOT be an artifact, IN THIS CASE. Thats why I believe Chris may have an unusual, but not unprecedented, case of a bad CAN bus module.

Of course, the CEL could come from the ABS code, and his scanner is simply not capable of indicating that one, in which case you are absolutely correct.

Short of a scanner capable of reading the C codes, Chris could unplug the motor connector from the ABS module and see if he has additional codes.

I also agree with your suggestion of likely RP causes, adding less likely, but reported additional causes of the brake light switch circuits not agreeeing (there are two switches and their states should agree), and intermittent knock sensor failures, which set a code on my car, but REPORTADLY sometimes do not.

Chris: Do you have access to AutoEnginuity software with Jag extensions, WDS, or IDS (those two legacy Jaguar diagnostic systems)? I think this is one that would really benefit from the dealer level software, both in reading all of the codes, including the ABS codes not displayed on most low end scanners, and in diagnosing the CAN failure, if it really exists.

 

The CEL can light - and you can have restricted performance or even the failsafe mode - without storing a code. (not a code that an off the shelf OBD reader can read anyhow)


I'd fix the ABS electronics as a first port of call. The Jaguar electronics give strange error messages that aren't consistent across all years of production. My favourite on an early X308 is a blown bulb filament in the "puddle lights" on the bottom of the doors. If the driver's door one goes, instead of the dash saying "by the way, the bulb failure monitoring circuit in the driver's door ECU has detected that the puddle light filament is faulty" they programmers programmed the dash to say "driver's door open" and illuminate the red warning lamp. Spent an entire day cursing the lock mechanism and microswitches over that one, only to find the puddle lamp later by pure chance! An ABS ECU that's a little squiffy could cause all sorts of interesting new functionality.


Good call on the brake switch. Absurdly expensive new (50 quid odd) but can usually be "fixed" by removing it, then bending the levers on the microswitches so that they both go "click" at the same time. A telltale for a bad brake switch is not getting any failsafe when driving aggressively (stomping on the brake pedal) but getting it when driving gently.


Favourite spot for CAN bus failure is the gear selector. The CAN bus to the engine and ABS ECU runs through it and the wiring is a poor design mechanically.


Dealer level software is handy. Fix what's known to be wrong first though?

 

Hmmmh. I would stand by my statement that no code = no CEL, but I have to agree with you that if your scanner did not read the model specific codes, you could have a non OBD code, a CEL, and not read a code. I have used IDS or AutoEnginuity for years, so have not experienced that.

 

Agreed - it'll be a non-OBD code making Christmas lights on the dash.

 

Hi
Here is a weblink to forum thread that also had a P1642 DTC that came up after erasing the P1638 DTC (View Post# 1 and Post# 10 in the following thread):

https://www.jaguarforums.com/forum/x...veryday-62726/

Issues were resolved by replacing the Instrument Cluster Module replaced with a used one.

Jim Lombardi

 

first, Ive never seen a reader introduce a can network fault, second can network faults with your level of scanner is pissing in the wind. You need to be able to look at ALL modules on CAN and they will give you error codes to help get closer to the fault. ie all the module are biitching about (lets say gear selector) EXCEPT the gear selector. Kinda like crazy, everyone around a crazy person knows that person is crazy, EXCEPT that person. Sooo the module thats generally not complaining is the one to start at. now theres alot more to this than just that and you have to know about general; failures like poor pin connection that need to be found by having the opposing correct pin to do a "pin drag test" youre looking for loose connetions at pins and are most commonly the result of intermittent connections and faults. Ive seen techs pin an entire can network and never find an issue with open/short/resitance and voltages. Only to have someone else step in and find the fault at loose pins theyre were pinning but never doiing a poin drag test for each CAN pin. This needs to be done BEFORE you start throwing modules at it. Then when youisolate to a module, swap in a known good one to verify and a new one. Im not going into more about this because frankly this is heavy diag and time consuming that Im not being paid for and really need my hands and eyes on. The best recommendation for futher DIY is check all connections especially the pins for CAN network and modules looking for back out pins loose pins spread pins etc. Female pins are the loose/spread pins, while female and male are common for back out pins. This you can do yourself but beforewarned, theres alot youll have to take apart to access the system connection and modules and you need the wiring diags. Are you really up for it? and be carefull, Ive seen welll meaning poeple and techs create new and more issues that resolvolving with these type repairs diag

 

Hi Brutal
I had to have two technical Jaguar expert places (they both have special scanners that read Jaguar modules) give me the fact that my Instrument Cluster Module needed replacing before I brought and had installed a used one (one was at the Jaguar Dealership Service and the other Indy shop Tech that has over 10 years as a Jaguar expert).

Jim Lombardi

 

Brutal:
I assume you do not use any of the elm based scanner interfaces or you would have seen that code, I believe.

 

Gents, Thank you for your continued interest in my P1642 problem.

I think I’m now experiencing an ‘information overload’ with the wealth of knowledge and advice the various posts and their links are throwing up…

Ross - The OBD scanner I’m using to be fair is pretty toy-town stuff (An ebay £60 bargain), and I doubt will read C codes. However, you are correct to note that the P1642 code is thrown with CEL & RP mode regardless of whether the scanner is connected or not. I haven’t taken the car to a main dealer yet as I am keen to save on the diagnostics / time costs. Since ownership I must have spent in excess of £2k on Jaguar’s ‘guessnostics’ and suck it & see approach to changing various sensors. Now that the XJR is not my everyday road car I’m happy to take my time and strip it to pieces if necessary. For the moment I’m going to put your brake light switch theory on ice, purely on the grounds that the CEL condition can occur within a few minutes of the engine being started and left idling (in park & without pressing the brake peddle).

Marko - I take on board your comments, but I’m not totally sure the root problem is the ABS. It’s interesting that you mention the gear selector as a possible CAN bus failure point. Before I replaced the alternator I had issues with the shifter interlock not releasing when the brake was depressed (this was also accompanied by the speakers emitting a truly disturbing interface type noise in relation to engine speed, even when the stereo was switched off, and the climate control panel beeping and displaying ‘ER’). However, these cleared after fitting a new alternator and I put this down to the old alternator having a faulty regulator / suppression unit.

Jim - The P1638 link made interesting reading, and confirms that the can bus network does indeed have ‘end of line devices’ which consist of 120Ohm resistor at each end which in theory should help in proving at least the continuity of the CAN Bus network using a DVO if nothing else. I hadn’t considered the IPk may be at fault here, but hey I guess everything on the CAN bus is up for grabs.

Brutal – What can I say?? It looks like I’m in for the long haul. Hopefully I won’t end up being one of the crazy people!

Today I tried an experiment by unplugging the ABS module (after clearing the P1642 code) and doing a ‘cold boot’ at the battery terminals. On starting the engine the CEL illuminated with the usual display messages. But now I have two new codes thrown up: P1637 (which I guess should be expected) and P1720. Good old P1642 is still present. Also the climate control panel beeps and displays ‘ER’ for a short period then seems to work ok. RP mode still follows shortly after the engine is started.

I’m tempted to have a poke around the gearbox control module which Marco mentioned. It may be worth me mentioning that in the first year I owned this car it knocked out three gearboxes. Luckily all replaced by Jaguar under warranty due to some faulty hydraulic component from Mercedes!!! I don’t recall the car going into RP mode before having gearbox problems and wonder if all the pulling about in this area has loosened some connectors? Worth a look see…

 

Daft question - how do you know that the P1642 is thrown if the scanner isn't connected? (my cheapo scanner throws the code as soon as it is connected in)

Second daft question - is your engine earthed properly? There should be a dirty great big earth strap between the bellhousing and the bodyshell. If a complete bunch of muppets (UK main dealer) changed three gearboxes they may have disturbed/omitted this strap, or not corrosion-proofed it appropriately. Without this strap the engine earths through...

...the gearbox selector cable, plus a bunch of other random things that don't really want big currents flowing through them. Nor does the alternator like having a poor earth.

The climate panel might offer some clues. Read up on JTIS how to interrogate it. (hold this button and that button and press the other button X times to flag up the fault codes) Then clear and see what, if anything, reappears?

Agreed ABS module doesn't sound like the root cause if it does it whilst sat there in park, and throws different faults without it connected.

Pull the centre console out to check the gear selector wiring; it's a pig to get to "through the hole" in the top of the console. Watch out for the clip on the top of the veneer surrounding the gear selector; it's easy to break off. It's probably already broken off if a UK main dealer has been in there...

CAN wiring runs through the little "illumination" module inside the gear selector housing and is badly strain relieved at the PCB. You'll want to check there, as well as at the plug connecting the gear selector to the rest of the CAN bus.

 

Hi Mark,

That's certainly not a daft question and one that I can not categorically answer for sure. I'm working on the basis that I can clear the code using the scanner (when it's connected obviously) with the ignition switch in P2. I then verify there are no current or pending codes and start the engine. Within a few minutes (even if just left idling) I get the CEL indicators / display warnings followed soon after by Engine fail safe mode. With the scanner still connected the P1642 code is then present.

I have already checked and cleaned all the main grounding points that I can find, and the one you mention did look suspect at the bodyshell end. However, the resistance between bodyshell & bellhousing was 0.01Ohms before I cleaned it up and dosed with some copper grease, and the same reading afterwards, so I guess we can eliminate this one.

Routing the CAN Bus through the gearbox illumination module as you describe sounds bizarre for such a critical network. But unfortunately, I've run out of time today to strip down the centre console, so I'll try and check this line of investigation during the week together with looking up the climate panel fault finding.

Thank you for your continued advice.

 

"Daft question - how do you know that the P1642 is thrown if the scanner isn't connected? (my cheapo scanner throws the code as soon as it is connected in)"

... Well, as I tried to postulate earlier, IF you get a CEL while the scanner IS NOT plugged in, and IF the only code you get is P1642 after you plug it in, (and now I add) AND IF your scanner can read all the codes, THEN it would have been the P1642 that set the code.

But, as you pointed out previously, IF your scanner will not read all codes, then a different code could have set the CEL, and you would not know it.

Unfortunately for Chris, it seems asif he probably does have a legit CAN bus fault since his explanation seems valid since I am pretty sure the "artifact" P1642 code has come up for me when I was using an ELM based scanner only when I first connected it, or, as I recall, just after I sent a "CLEAR FAULTS" command.

 

Hi Ross,

It's possible our last posts crossed over looking at the timing.

My earlier opening para may shed some light on my theory regarding the Scanner causing a P1642 code?

Your point that there may be other codes setiing CEL & RP is very likely given that the scanner I'm using isn't top end stuff and may not be picking up these other codes.

 

Chris:
Sorry i was not clear! I liked your explanation that the CEL came on at the same time that your previously connected scanner posted the code. As Marc and I have been pointing out, many, many posts on here indicate P1642, but very few (although some!) are actually a CAN bus problem. When I used to use an ELM based scanner, I got P-1642 about 25% of the time I connected my scanner.

As Brutal has told you, and I have alluded to, CAN bus diagnostics are a PITA (do you know that acronym?), so the trouble shooting method of eliminating alternatives might be best in this case. So, checking the ABS module, at least by unplugging the motor to see if you get a different response is valid. So is continuing to check the grounds in all the modules. If you had access to an oscilloscope, there are some tests you can run.

You seem like you have a technical background and can probably diagnose most things in an X-308. If you plan on keeping the car, I would suggest you consider buying (or finding a friend with!) a so called advanced or dealer level scanner. I have AutoEnginuity with Jag Enhancements, and IDS, connected via a VCM module which costs a small fortune. There are posts in the General Tech section about a new interface optin called a Mongoose which is a good bit cheaper. I do not know if it will scan an X-308.

If there was not a big pond between us, I would say drive over to my house and we could hook thge car up and see if we could find it.

Anyway, with the advanced scanner, you can read each module's parameter and faults. So, for instance, in your case, you could both read the ABS and other module's Fault table to see what might be lighting the CEL besides P1642, aand you could read diagnostic parameters from many of the modules which will point you towards who is the CAN bus problem, as Brutal suggested.

While none of the advanced scanner options seem cheap, they can be economical versus taking the car to the main dealer or throwing parts at the car to find a problem. That said, many guys on here do just fine keeping their Jag running without the advanced stuff. My wife and I both drive Jags as our perimary ride and put a lot of miles on them, so for me, the advanced software is a necessary tool, just like my torque wrench.