Spent a lot of time lurking on this forum, but finally had a reason to post so here we go.
I bought a 2001 XJ8 in January. It had a check engine light, which I promptly had the codes run on, ended up replacing the entire VVT unit. Tensioners are done, water pump replaced, new tires, new battery, the whole nine. Had no issues from it other than the suspension is a little noisy.

Last month, I started getting intermittent ABS/ASC lights on the dashboard that happened once or twice, but cleared when the car restarted and didn't happen again. I took the car on a road trip last week, ran smooth like a dream there and back.

But once I got home, the next morning, I started the car up, pulled out of the driveway and there was a Thump from what sounded like the transmission along with the "Gearbox Fault" display and a significant loss of power. I parked the car overnight, and when I started the car back up there wasn't a light on the dash. Started to accelerate and the thump happened again along with the same message, except this time, when I accelerate, the whole dash display will light up with ABS/ASC then a check engine light, then it will get dim and only have a check engine light in addition to a 'battery not charging" display. My windows will lock up, and at one point the windows went down an inch. The brightness changes on the dashboard depending on my acceleration or breaking or at least is random from what I can tell. When I restart the car, only the amber check engine light is on, and at least two times I've driven the car and not had this whirlwind of nonsense happen before.

I'm especially concerned since in Memphis there are so few people who work on these cars it's almost impossible to get it diagnosed, but I'm looking for anything I could do myself with minimal headache that might cause all of these issues. There seems to be some random stuff going on with the electrical side of things, but Im not sure where to start. There's a wire that's hanging oddly low on the passenger side near the front wheel. Anyone who's had something remotely like this happen I really could use some advice.

 

When a sea of Christmas tree warning lights, CEL, and unexpected behaviour hits, it is easy to panic and attack everything in all directions. Take time to assemble a careful (and logical) plan . . .
.

• Have you checked the battery? What is its standing voltage? Remove and clean terminals (at both ends) then hard reset;
• Have you checked main distribution circuits for loose connectors, poor ground fixings? Corrosion or loose joints are well known issues;
• You have codes? Then list them here . . . be specific and be accurate. Beyond the generic OBD codes, transmission issues may require you to go TCM;

There's more, but given your worry-free road trip and issues in shorter stop/go, I see these as logical start points.
Cheers and best wishes,

Ken

 

check the ground on the fake firewall

otherwise it could be the alt

 

Don't push the transmission as it clunks , further damage can accrue

Pressure regulator fault with the ZF5 HP24 transmission ?

" Battery not charging " points to a bad alternator , it must maintain at least 13.5 volts at the large B+ alternator post which you may or may not see duplicate in the driveway with a warmed up alternator { put on a good electrical load and throttle the engine up and down )

Check the terminal nuts on high power bus protection module ( fuses ) that has a history of coming loose , see page 39

There are 4 number of fuse box relays ( labeled ignition positive , auxiliary positive , and EMS control relay ) that one may be intermittent on page 39

Note that not all fuses in each fuse box relies on the relay to close , about 1/2 of the fuses are directly wired to the battery as hot at all times

Note in order that the relays close the ignition switch provides the relays with a command ground , the ignition switch connector about 6 inches away can get corroded by fluid spills . and the # 5 pin on the car half of the connector to car frame ground can be disturbed or compromised

http://www.jagrepair.com/images/Auto.../jagxj1999.pdf

I don't know of a swapping option so you may have to obtain a new one to try

You can narrow down which specific fuse box by a list of the faults that accrue at the time of failure



This switch can be tricky to interbit with a mater so it's not the most confidence building

 

Alright, had some time to check a few things, going to be running through a lot more tomorrow. Battery sits around 12,6 when the car is off and can range between 14-19v when the pedal is depressed.

Got the codes checked at AutoZone and only got one code- P1793

Cleaned one side of the false bulkhead connection that was a little dirty, didn't realize the other side needed to be inspected too.

I've seen a few posts on the forum about this code being a sign of a bad alternator, but the battery seems to be charging when the car is on-maybe a bad voltage regulator that's causing the fault?

After a reset and cleaning one side of the false bulkhead connection, the car ran like normal, no gearbox fault, all dashboard looked fine, 30 min later when I'm barely touching the gas the fault happened again.

Would the tbps give me a fault like p1793? I'll check back tomorrow after I check and clean all the grounding points.

 

If your voltage can go as high as 19 you definitely have a regulator problem. The codes read by a generic reader are only P codes, but they do not report C and U codes which relate to chassis and communication system faults and require a Jag specific code reader.

 

RJ237,
What scanner should I be looking at purchasing? All but a couple of shops in my city even work on the 2001xj8 and even the local dealership here doesn't work on pre-2005ish jags. Not sure where to go to get a full scan or which scanner to buy

 

Forgot to mention I've been getting no answers on the phone from the two places that work on my car in the city so I'm feeling a little helpless

 

Sounds like a voltage issue??
Check the DTC guide for info.

 

Best to read the large B+ terminal post on the alternator as more accurate of a reading then through the losses in the battery cable connections

In practice you would see a lower voltage at the positive battery post then at the alternator connection

In your case your reading is not stable and swings to the overvoltage side

Your next step is replacing the alternator and your code and other symptoms may disappear

The regulator is inside the alternator and you can replace just the regulator but test the rebuilt alternator assembly before installation

A spin up bench test of the alternator be it one off the shelf or a rebuilt one will not fully duplicate a real operating environment but if it fails on the bench saves the installation headache

 

It is EASY to get to the FALSE BULKHEAD electrical connector that goes from the ALT/STARTER directly to the BATTERY.
Good place to get a reading and check to make sure it is a TIGHT and SECURE connection. (not burnt)

 

​​​​​​ITs definitely a voltage issue-wanted to share my notes:



Started the car up, no check engine light, no dashboard warnings THIS IS ALL WITHOUT DRIVING THE CAR OR SHIFTING GEARS I don't know if that's a big factor but I thought I'd make a big deal of it

Battery Connections and all the high power distribution studs measured 12.69V with the car off

At idle, battery and all high power distribution measured 13.86V
​​​​fluctuated to 14.5V or so

At idle, across the bulkhead connection I got 6.8-7 MILIvolts this is after removing them and cleaning them thoroughly
Throttle body to shock tower measured 198MV after waiting for a while, hit 200mv then started climbing from zero

motorcarman-- from the throttle body (neg) to the bulkhead connection was a steady 14.5V at idle and when applying the gas it stayed pretty consistent. HOWEVER

​​​​​​After shifting into reverse then to drive and driving up the driveway 40 feet or so, the thump happened and all of the lights came back on
​​​With the car in park, the bulkhead connection was spitting out all kinds of craziness- looked good 14.5V then would drop to 3V then back to 14V then down to 9 then a second of 18V. When applying throttle it would even out to 14V again and after the revs slowed down would jump all over the place again.

After turning the car off and back on again, everything is back to normal-the check engine light sometimes will and sometimes won't be on.

Now I haven't replaced or removed and cleaned the ground strap from under the car, but it is disgusting and looks pretty rough, plan on doing that either way soon.

Found the inertia switch and it depressed and clicked, didn't seem to change anything.

Seems to me like the voltage regulator is out on my alternator. At least as far as my limited experience and hours on this forum can tell me.

Tiny note that may or may not be important- I've had issues with the lock on the driver's door handle, sometimes I can pull it and unlock the doors but 9/10 times I have to unlock the car before I turn it off or I have to use my key fob to get out of the car. And also, since all this craziness has started, after doing a hard reset:

1. It didn't ask for a radio code (I have it)
2. The driver's seat does not return when turning the car off.


I'm having a hard time finding the connector that was mentioned above for the ignition switched power supply, does anyone have a picture-im not sure if its relevant but I'd like to know for when that goes out later on.


​​​​​​TLR: alternator output after driving the car briefly (after triggering fault) jumps all over the place so I'm assuming it's a bad voltage regulator based on the P1793 code and the cars behavior. Any help on any part of this would be great!

​​​​​

 

The seat not moving after key removal could be a stuck linier key in and out switch inside the rotary ignition switch

This closing of pin 4 to 5 triggers the security lock control unit to began it's sequence to exit the vehicle like automatically ( if selected ) repositioning the steering column and eventually going to the sleep mode thereby not draining the battery

This can be cleaned and lubed in different ways

The rotary contact making of the 1 , 2 , 3 pins to 5 is not the most confidence building as more then one pins closes at the same time , the starter pin is a momentary contact which can waver on your meter

Note that this switch is only as good as the pin 5 on the car side of the connector having a good car frame ground

The picture is after you remove the bottom small curved cover under the steering column and is the switch side of the connector , the car side connector lifts straight up and unclips to bring it out to you

You don't have to remove the switch from the back end of the key barrel at this time

Seems to be 2 problems both the ignition switch key in key out and your regulator control should not get over 15.0 or under 13.5 volts so you can fix up the ignition switch first

There is a fuse ( # 2 / 5 amp engine compartment fuse box ) to power the voltage regulator . This relies on the engine compartment relay ( referred to as ignition positive relay on page 39 ) to close which is controlled but not powered by the ignition switch at pin 3

You have seen where this path runs through the inertia switch which can not always reset or be intermittent and you can override with a paper clip between the 2 white wires on the inertia switch connector

If you open up the inertia switch parts will fly everywhere , ask me how I know .

See page 49 , power point 8 stop sign double hash on the right side of the print

http://www.jagrepair.com/images/Auto.../jagxj2001.pdf

 

Got a rebuilt denso alternator and replaced it myself yesterday, all problems solved. Will be checking back in after looking at the ignition switch. Took me many more hours than it should have but got it done. Thanks so much for y'alls help!

 

Hope it’s ok to put my problem on the end of this post, seems to have simularities.

I have a similar issue, just started one cold morning on start up, car is in limp mode, car moves, no acceleration (because of limp mode), grabs in reverse, not sure where to start, GEARBOX, AIRBAGS, ABS or as stated here Electrical.

any help appreciated, thank you, have read plenty of posts on related issues.

# I will check battery voltage, but it is a relatively new battery, 1 year old and heavy duty.
# Seat belt tensioner ?
# Codes, my code reader is wrong type for Jaguar, will see if I can get one !
# ABS sensors on wheels, will give them a clean.
# Checked Brake Fluid level, topped up to maximum.
# ABS Pump and Board, soldered joints ?
# Gearbox speed sensors, including check GB fluid level, change Filter & Fluid, replace Pressure Regulator Valve with ………Transgo Kit! Or connectors?
# Steering Wheel airbag and or steering lock/ connectors?
# link to ZF 5HP24
https://aftermarket.zf.com/remotemed...pdfc-5hp24.pdf
#

 

It would be better to start a new thread. You may have two problems: a low battery and a failed a-drum. The low battery is easier to resolve, charge it and check that you have at least 12.5V read with a voltmeter, not the dash instrument.

 

With a ELM - 327 device you can watch to see if the voltage regulator is stable and recovers after RPM change

Otherwize you can put a meter on a glove box light bulb socket with an assistant during a drive

The unstable voltage if there my be too short a time to get a alternator light

 

Hi thanks for the reply's
When we say failed drum are we talking cracked, can we see that through the inspection hatch on the bottom of the transmission/gearbox, or from particles of metal if I undo the bottom cover?

jagger98

 

If it's cracked you would not see that until disassembled.

 

Ok, I have a code P1793 which just confirms what’s on the dash!

Battery, a year old, more interesting, terminal had corrosion all over it, the battery was leaking and it looked like it was bulging out at the ends

While running, put a meter across the terminals and it was reading a whopping 18 volt, so it looks like the alternator is up the swanny, hope that’s a correct assumption.

! would that cause the dash errors, airbag, stability control fault, probably not the Gearbox fault?

anyway, Alternator is undone,1 x BOLT top 10mm, one bolt and nut on bottom, here’s the interesting question, what’s the best way to get it out

1. take the Alternator bracket off and oil filter, feed it through there, or

2. remove fan cowling and squeeze it through there or

3. somewhere else

jagger98











I found this from member Doug, sounds like a good idea.