Hello everyone!

My XJR, which is being used as a daily driver for one and a half years now, has had the first "issue" today where I am not yet sure what to think of it.

It started on the morning commute to work, low temperatures, roughly 1min into the journey. Whilst going over a speed bump at low speeds I pushed the accelerometer ever so slightly to get to the next stop light (must have been between 15-20mph, assume it was on the 2nd to 3rd gear change) where you could hear the load of the engine increase yet no increase in RPM which was a weird noise to say the least. A few seconds later the car started to shake, vibrate and threw the warning "limp home mode" and "stability control fault" - nothing else. I could not stop due to traffic so I had to drive a couple hundred meters down to road for a quick stop. While shaking and vibrating the gear changes still felt pretty smooth and normal. At the bay I shut the car off, started again and all was back to normal - no issues since. Gear changes are silky smooth as usual and be it in C or S mode on the gearbox, there is no notable issue to be found other than the following: When creeping along in traffic <20mph in 2nd gear the car starts to accelarate slightly instead of slowning down gradually. Like the gearbox is enganged too long.

Has anyone experienced such a behavior? I have not had the chance of getting a code reader.

Gearbox is the MB722.2 / W5A580 transmission. Oil and Filter are new as well as the electrical connerctor on the right side which is known to leak.

Thank you for your help,
Oliver

 

Are there any DTCs logged in the TCM?

Faults usually leave a message in the TCM for diagnosis.

I usually check ALL the modules in case of a CAN bus fault or other network issue?

 

You're right, I will check today if there are any faults stored in the TCM.

Just for myself, am I looking at the wrong place or can the transmission really be the issue? I've noticed the following:

- "limp home mode" and "stability control failure" shown on dash, no CEL
- car stays "in gear" too long and wants to push the car forward, even when letting off the gas or braking
- when at a stop light in D on the brake the RPM goes from 800 to 400 to 1200 randomly
- when putting into N, the RPMs go to 1200 for some time until they come back down to 800 (normal)

Does anyone know how the engine and transmission communicate? It seems that the transmission has lost some of its input

 

Low alternator output (voltage) can sometimes cause similar symptoms. It is easy to eliminate, just check the voltage on the battery terminals while the engine is running.

 

The INSTPK, Gearbox Selector ILLUMINATION MODULE, ECM, TCM and ABS are all on the CAN bus as illustrated in the electrical guide (S98_SED.pdf) on page 19.1

The guide is about 9mb and I'm sure Gus has it on his site (jagrepair.com)

 

Hi Oliver,

I assume your transmission is the electronically-controlled 722.6 rather than the earlier hydraulically-controlled 722.2 (which had no protective Liimp Home Mode).

A couple of things come to mind with your symptoms.

The first is that it is not uncommon for the electrical connector at the transmission to become contaminated with transmission fluid due to failure of the O-ring seals on the electrical connector sleeve. Access is a bit tight, but you can disconnect the harness from the transmission and inspect the harness and transmission connectors for oily residue. I don't recall it being an issue on Jaguars, but on some Mercedes vehicles the oil has even been known to wick up between the conductors in the wiring harness all the way into the Transmission Control Module in the engine bay.

The second thought is a potential problem with the conductor plate inside the transmission, such as intermittent failure of a speed sensor, which is very common with the 722.6. Usually you will get codes related to the speed sensors. The recommended repair is replacement of the conductor plate, but it is often possible to replace the individual speed sensors. Search "722.6 conductor plate" to see many threads on this topic in Jaguar and Mercedes-Benz forums.

Bob's question about Diagnostic Trouble Codes logged in the Transmission Control Module is important and may help you narrow down the cause of the malfunction.

Cheers,

Don

 

These are the TSBs we got in the early 2000s for the W5A580.

 

Hi Don,

thank you - your input is truly appreciated! I have already changed said connector less than half a year ago but the conductor plate seems to be the culprit as you said.

I will order the plate and give feedback if that has cured my "issue". (Which has been absent again for the past week).

Cheers,
Oliver

 

Thank you Bob! The TSBs will help. As Don stated I am going to get a new conductor plate as well.

I will get a reader and will be back with the codes that have been stored.

 

Hello everyone!

A short update with a couple more questions arising! I am not sure if we are searching in the right place. Hopefully someone can assist with some further thought.

A short overview:

- The issue started three weeks ago (problem stated in post #1)
- The issue is very intermittent and was not to be noticed for almost two weeks in a row.
- The are NO fault codes stored or to be extracted
- The transmission speed sensor seems to be quite the issue on many MB 722.6 gearboxes (the whole repair kit has been ordered - not yet arrived). Thank you Don for the tip!

Today the car started acting up quite extreme and "more" issues added themself to the mix. Is the issue somewhere else?
The acting up started right after one hard pull in second gear (previously without issue that night). ASC did interfere as the road was damp.

0) When in manual mode (2 and 3) and accelerating normal through the revs, the engine stutters or judders very slightly for a lack of better wording. It feels like the transmission though and not like an actual issue with the engine yet I could be mistaken. The engine has always full power.
1) When in D and let of the brake pedal, the car moves forward very aggressively (stops accelerating by itself but much later than without the issue)
2) When in D and braking, the car "pushes" against the brakes quite hard before letting off and disengaging the transmission at full stop
3) RPMs are between 800-1000 in N and P (Idle is 600 when normal)
4) When revving the engine at higher idle in point 3) the revs keep locked at 3000 for a couple of seconds before returning back to 1000
5) RPMs at higher idle are still smooth and nothing here is lumpy or rough
6) No CEL or codes can be seen or extracted
7) Issue is usually only noticeable at lower city speeds with no cruise control
8) Today at highway speed (120kmh) with activated CC the issue was noticeable. Like pushing the gas and letting off again.
9) There is no big difference if the car is cold or hot. Only the downshifts are smoother when hot. Up shifts are silky smooth regardless.

Being worried that something is wrong with the TBA I did the following:
- Cleaning of MAF and Air Filter
- Intake tupe and load breather checked for leaks (duct tape on breather pipe)
- All connections of the TBA cleaned with contact spray
- Cleaning of the TB (has been very clean before)
- Adjusting the throttle cable one turn (was good before)
- Hard reset

Now the car drives, revs and shifts as perfect as it always has. (Just a 20min long city commute)

Any ideas where the issue could come from? I am still very convinced of the speed sensors of the conductor plate of the 722.6 transmission.

My XJRs built date is Nov/1997 (AJ26)

 

Hi Oliver,

The first thing that comes to mind is fuel delivery. Have you checked your fuel pressure at idle and under load? A fuel pressure regulator that is binding could cause intermittent elevated fuel pressure, which could increase engine rpm.

I am attaching some TSBs/diagnostic guides related to engine hesitation and other driveability issues.

Your mention of tape on the breather hose reminds me of a cleaning procedure for the part-load breather port - see the attached TSB.

Cheers,

Don

 

Rpm is limited when reving in N or P to the 3000rpm. Those mentioned symptoms, pushing too much against brakes and letting off after some time by itself leads me to the gearbox turbine failure. More specifically to the turbine lock that stays on when it should not. It can cause feel of engine misfire.

 

Hello everyone - I am back with some updates and slightly more confused that I was before.

@Don B - I have not checked the fuel pressure yet, Maybe we really have an issue here as I will explain below. Is the FP under load checked with engine running and revving in P or N or while driving? PS: The part breather hose has been cleaned two times over the last year with no notable built up.

@Vauxi - Good point. Would that issue then be permanent? The funny thing is, that this is very intermittent and the car drives excellent for weeks and then displays the issue. The XJR is a daily driver and I drive it short, long, soft and very fast. Yesterday over 230kmh without any issues.

UPDATE:

Pre replacing of parts: After doing what I have stated a few posts above (inlcuding hard reset) the car behaved very well during the following 8 days to get the parts (below) changed. No big issues other than two bad shifts, where it was reving too high before changing gears.

Parts replaced: I did change the conductor plate of the transmission (as we have thought to be the issue), including the electrical connector, seals, filter and oil of the transmission. Despite having shifted nicely before the car now shifts even softer and quicker. Two weeks of daily driving without a single issue - I thought we did solve it. I did not change the sensors or valves itself, just the conductor plate.

Issue still here: Yesterday it started again and what I am to explain sounds probably very weird. Ive been on the road for 10min in average traffic (50kmh) in the city. After a medium sized bump in the road it started right away (it did the same thing the last few times so it must be something with shaking the vehicle). The car started to being very jerky like it has bad plugs, doesnt get any fuel etc AND the gas pedal was moving by itself. The cruise control was off and deactivated during that occurance. (I hope my CruiseControl works correctly but on the highway when selecting a certain speed something pulls the pedal every so slightly away from your foot and "lets go" once I deactivate the cruise control). I say this because the feeling was similar. The car then displayed the same symptoms as I have mentioned in this thread. Being jerky, pushing against brakes, too high idle etc. After a few minutes the fault did disappear by itself and I continued the journey home uninterrupted.

This morning was similar. Right after startup the car was jerky, that did end right quick though and the car resorted to the similar issue of pushing against brakes, letting off too late, too high of idle (D N and P). Apart from that, shifting and driving is normal. Car has full power at WOT.

Has anyone more ideas or are there more problems occuring here at the same time? The are no codes stored and no fault messages on the display.

 

Hi Oliver,

I'm sorry to hear that your XJR is still misbehaving! At least the work you have done will contribute to the long life of your car.

A few thoughts come to mind. Sometimes issues like this are due to multiple systems being a little out of range.

1. Ideally, to test the fuel pressure under load, I connect a fuel pressure gauge to the fuel rail with a hose long enough to reach through the driver's window so I can set the gauge on the dash/fascia. Then I can monitor the gauge while driving and can see how the pressure compares at idle and cruising with accelerating and climbing steep hills.

2. Looking back at your previous posts, I was reminded of the duct tape on a breather pipe. This makes me wonder if one contributing issue is unmetered air causing lean running, but not lean enough to trigger lean DTCs such as P0171 or P0174. Can your scan tool monitor the Short Term and Long Term Fuel Trims (STFT & LTFT)? It would be helpful to know if your engine is running lean. Which reminds me, how are your coolant thermostat and engine coolant temperature sensor behaiving? If the thermostat sticks open, or the ECTS fails at a point that tells the ECM the coolant is always cold, the ECM will continue to apply cold-start fuel enrichment even after the engine is fully warm.

3. Can your scan tool read the Network DTCs (U-prefix)? It would be helpful to know if perhaps there is an issue with CAN communications.

4. It might also be helpful to know if there might be an intermittent issue with the ABS system, since the vehicle speed signal comes via the ABS wheel speed sensors (maybe the rear right sensor on your car, but I'd have to look it up to confirm). The vehicle speed signal is critical for the ECM and TCM to orchestrate smooth gearshifts. Any intermittent interruption in that signal can cause shift problems.

5. The vehicle torque signal is also critical for smooth gearshifts, and it comes from the MAFS. I know you cleaned your MAFS, but at this age I have come to feel it is good maintenance to replace the MAFS with a high-quality new one (Denso) if you can find one. The only place I could find one for my '01 XKR was from Jaguar.

6. It also seems possible that you have a problem with the throttle position sensor (TPS) and/or accelerator pedal position sensors (PPS or APPS), which work together.

7. The fact that the problem manifests after hitting bumps seems relevant, and makes me think about a loose electrical connector, pinched electrical harness (how are your engine mounts?), or a loose or cracked air intake or breather pipe.

8. Does your car have the evaporative emissions system with charcoal canister, canister control valve and purge valve? Leaks and stuck valves are common with the EVAP system but will typically trigger DTCs.

Sorry to throw out random ideas, but you definitely have a mystery on your hands!

Cheers,

Don

 

Bit late to this thread and I can only echo Don's suggestions. I did think yup unmetered air leak, but 3k rpm is hmm.

The bump seems a strong case for the limp mode, and an ensuing electrical fault.
Have you put your inertia switches in their correct places? I'm not sure it's related, but did you work on these in relation to the fault?
Trans adaptation after the service work?
Has your car had the 'gold pin kit' on the throttle body connector?
Wiring connections and the main power lead, have a good clean up of the link lead ring connectors to and between the under bonnet fuse boxes.
Also treat your earths to the same.
A guess...
Seems like it goes Bump - hard reset - attempts to recalibrate - in drive against brakes - which must be rather unpleasant.
In which case it's pointing towards a main power harness/earth issue.

 

Yes, as Sean noted , the fault occurring at a point where the car is being jarred by a speedbump
sets off some indications of electrical problem(s). I would first check your grounds and go from there.

 

Hi Don,

thank you very much for your advice! This is truly more than appreciated.

I did answer inbetween your points for easer reading in blue.

 

Hi Sean,
thank you for joining and welcome to my little issue.

• True - while fuel pressure and unmetered air can be an issue I can only confirm that the car behaves normal and has full power when not having the whole array of simultaneous issues.
• It was only an observation with the bump. Especially weird with the "self moving gas pedal" right afterwards including all other issues. Then they tapered off one by one and the car is absolutely normal over the past five trips. It is a daily driver, so big bumps occur all the time.
• Are these for accidents and fuel cut off? I have not touched them and did no real work on vehicle over the last two months.
• Yes, the whole work has been carried out by the official workshop at Mercedes Benz Vienna. Shifting has been great and is even better now. Also when the car is having all of its issues, the shifts are fine and not a problem.
• That is a good point Sean! I have read about it but where exactly is the gold/tin pin connection? LHS or RHS? I have a sticker with an eye on my TB and it slipped my mind but I recall this to be sign of an exchange part?
• Good point as well. I have a new connector on the false bulkhead. The old one was melted and therefore couldnt turn the starter motor anymore. I will check all my ground points on the car. Just loosen them, clean, back together?

Yes, it is very unpleasant but not too extreme. When having the issue the car goes from impeccable to being jerky in gears, having too high idle, driving away too aggresively, speeding up to 50kmh by itself, pushing against brakes until finally getting in neutral etc. All this while no codes or messages are displayed and these issues taper off one by one. First the "jerkyness" stops, then having just high idle and self accelerating which also tapers off. The last two days and five trips (daily driver) have been impeccable again.

 

Hi Randy, thank you for confirming. I will check all my grounds, clean them and will report if I find anything. Do the big ground wires need changing alltogether or just a good clean up of the attachment points?

 

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