been a while

car stuck in 3rd with tranny light on and engine light on.. starts up and drives perfect but wont shift.. i used to be able to shift with J gate but now it wont do that... side note.. Sport mode doesnt work either...

i cant seem to find the culprit to this issue on here. can anyone point me in the right direction to this? maybe i missed a post somewhere, or if anyone knows off the top of there head. much appreciated.

1990 majestic 90000 miles

 

The gearbox is in 'limp-mode'. If you had access to a PDU you could read the DTCs from the TCM. WDS or later diagnostics will NOT read the gearbox codes.
Could be the harness plug on the gearbox, throttle position sensor, faulty blue Hella Relay (power to the TCM)???????

bob

 

Hi Marco,

Your Majestic is a rare and fine automobile, and I'm sorry to hear it is malfunctioning.

On our '93, Limp Home Mode (LHM) has most frequently been caused by oil contamination of the electrical connector for the Throttle Position Sensor (TPS). The TPS is mounted on the bottom side of the Throttle Body (TB) and on our '93 the electrical connector is mounted on a bracket fixed to the intake manifold elbow just to the left of the TB. Separate the two halves of the connector, flush them with zero-residue electrical contact cleaner spray (available at any auto parts store), allow to dry, reconnect and test drive the car to see if the LHM is resolved.

On your 1990, the Transmission Relay is located behind the right or passenger side knee bolster. The wires that connect to the relay are Brown/Green, Black, White/Pink, and Brown/White. Check the socket for corrosion - if you see any, disconnect the negative battery cable before cleaning the socket with a small wire brush and contact cleaner spray.

Another possibility is looseness or oil contamination of the electrical connector on the transmission itself that Bob mentioned. See the photos at this link:

Welcome to Jag-lovers - Members Photo Viewing Page


If cleaning those components doesn't do the trick, there is an excellent diagnostic routine in the XJ40 eBook at the Jag Lovers forum (jag-lovers.org). You'll have to join to view the eBook, but it's free and well worth it for the wealth of information available in the archives of that forum.

Two of the three grounds used by the TCM are unfortunately somewhat difficult to access, one being on the transmission tunnel and one on the bulkhead/firewall behind the left blower motor duct. The third is in the engine compartment on the right side bulkhead/firewall and it would be worth removing the nut, cleaning the threaded stud, all the ring/eyelet terminals and the nut with your small wire brush and contact cleaner, allowing to dry, then reassembling.

The TCM Bob mentioned is the Transmission Control Module, located behind the passenger side knee bolster. The photos at the link below show how I repaired a cold solder joint in our TCM that was the cause of our most recent LHM in our '93:

Welcome to Jag-lovers - Members Photo Viewing Page


To see the electrical circuits involved in Transmission control, see the last schematic in the 1990 XJ Electrical Guide, which you can download at this link courtesy of our forum member Gus:

http://www.jagrepair.com/images/Elec...Electrical.pdf


Please keep us informed.

Cheers,

Don

 

thank you Don and Motorcarman for the replies! i will get to work and see what the results are! got to wait for work to let out.. getting anxious

 

I uploaded hundreds (thousands?) of TSBs and other info to the large file area (media-fire account) and this is among them.

Here it is again. It should be renamed 'CRAPPY BLUE HELLA RELAYS' (apologies to Thomas Crapper).

bob

 

forgive me for the delayed responses... life gets in the way of getting the beauty back on the road..

i plan to go thru the full trouble shooting procedure from jag lovers this week to iron out this issue once and for all...

turns out ive been too damn busy to get in there and do some bench testing on the relay, tcm, etc, but i did get a chance to check them out visually, and ive notice they are all black hella relays, dunno if these are of better quality than blue? and quick little Q.. would the check engine light come on if limp mode is on as well on the 1990 xj40?

edit: another note, it makes a violent "thud" when put into reverse.

 

Hi - if your check engine light is on, you should have a fail code that can be read on the odometer panel. If you turn on the ignition (don't start the car) and press the VCM button you will see a message on the LCD under the speedo, something like "Fuel Fail" and a number or "FF" and a number.

Post that message here.

Sorry not had any tranny issues so unable to help with the problem other than suggesting you check the fluid level correctly. There are threads in the archive as how best to do this.


Larry

 

back at it

So i cleaned the plug on the side of the gearbox and no luck.. i attempted the rotary switch as well and its far too corroded right now so i sprayed some penetrating fluid on it to loosen the bolts, ill get to that today. Now, i took a look at the TPS red casing and its covered in grime.. could that be an indication of it faulting? it seems like a bigger job than the rest because i have to take of the throttle body and part of the intake manifold bellows to get to the bolts. so is there i way i can test the TPS with a multimeter thru its plug? or should i just take it off and inspect it, but id hate to ruin the calibration of the tps by taking it off...

 

The oil filter and/or housing can be removed for access to the TPS. You can just use a moving coil ohm meter to watch the 2 sensor tracks (6 wires, 3 for each). There is one for the ECM and one for the TCM.

The problem with a digital meter is that you can't really watch the movement for SMOOTH transition from one end to the other. The meter will jump the digits and you might not notice a fault in the potentiometer tracks. A needle on a moving coil meter can be watched for the needle JUMPING when a bad spot is encountered.

The Black Hella relays were not know faulty like the Blue ones (or they were already replaced?).
bob

 

Yes. You can back-probe the plug by pushing two paper clips into the back of the connector and connecting the clips to a meter. Moving the throttle by hand through its range will reflect on the meter readout.

The idea of using an analog meter as Bob suggests seems like a smart move (if you can get your hands on one!)

Larry

 

Is it possible to clean the tps without removing the tps from the throttle body? or is it as simple as just marking the spot its in now with a sharpy then lining it back up when reattaching it (if that makes any sense) instead of re-calibrating it?

and another quick question... is my LHM light supposed to show up immediately when i start the car after resetting the computer? i figured it would stay away for a minute then pop up..

 

Hi Marco,

Have you tried simply cleaning the electrical connector for the TPS first? That's been the most common cause of LHM on our '93 and it's an easy fix.

If that didn't work and you really want to clean the TPS itself, it needs to be removed from the car to do the job properly. Yes, you can usually get away with marking its location on the TB and returning it to that position, but in my opinion it's just as easy to remove the entire TB with the TPS attached. Because the TPS is mounted on the underside of the TB, oil and other gunk drawn into the TB through the crankcase breathing system drains down the shaft of the butterfly valve and collects in the TPS. Like several other owners, I drilled two drain holes in the case of our TPS, flushed it with zero-residue electrical contact cleaner spray through one hole until the fluid coming out of the other hole was clean, then left the holes open so any future oil and gunk can drain out. See the photos at the link below:

Welcome to Jag-lovers - Members Photo Viewing Page


If I recall correctly, LHM is triggered by the Transmission Control Module (TCM), not the Engine Control Module (ECM), and disconnecting the battery to reset the ECM may not reset the LHM status in the TCM.

Cheers,

Don

 

Okay so i replaced the TPS with a new one and nothing. i also removed the TCM, opened her up and checked boards for any noticeable faults.. nothing, looked brand new. i replaced all fuses, which made the "bolt light" go out so now i only have a LHM and a CEL on.. . Relays have all been checked as well... im starting to lean towards the rotary switch but the damn thing is soooo corroded on the outside that i snapped 2 bolts already getting it off and now its pretty much impossible to get into it, should i take her all the way off and try to dismantle her on the work bench?... any ideas what to do?any way to test the TCM for faults or issues?

id really hate to get rid of this car for somthing like this.

 

Hey Marco, don't give up just yet!

We've all had these "insurmountable" problems but hopefully with perseverance eventually get resolved.

Rotary switch can be replaced - probably have a good one on my parts car - not sure if the vin's/trannys match up though, but if not I'm sure eBay will have one.

You still have the check engine light on, right?

What code displays on the VCM?

Larry

 

just checked my vcm and its reading just "PAD"... ;(

(keep in mind the LHM light NEVER goes off even after battery unplugged for days... does that mean the tcm is bad?)

 

So just a low brake pad warning then?

You don't usually get a CEL from that (AFAIK), but hey that's what you got!

What's up with that Don? Multiple codes stored?

Larry

 

Hi Marco,

When it rains it pours! As Larry suggests, you may have multiple fault codes stored. The PAD code probably means a brake pad wear sensor has worn through and opened the circuit. I think on a '90 there are two pad wear sensors, one on the front left wheel and one on the rear right. The PAD warning won't clear until you either replace or repair the opened sensor or short across the terminals in the electrical connector to complete the circuit.

You say the relays have all checked out - I assume you tested the transmission relay and it is working properly and there is no corrosion in its socket or on its terminals?

Another suspect is the fuse that supplies the TCM or cold solder joints in the fusebox. Here are some photos showing what to look for in fuseboxes:

Welcome to Jag-lovers - Members Photo Viewing Page

It will be worth checking the interior of your rotary switch - perhaps several applications of penetrating oil may help remove the remaining screws. Here are photos showing the internals of the switch and how I cleaned ours:

Welcome to Jag-lovers - Members Photo Viewing Page


If the rotary switch solder connections look good and the switch contacts look clean (clean them anyway), I would recommend that you follow John Ping's excellent transmission diagnostic routine that can be found in the XJ40 eBook at the Jag-Lovers forum. You will have to join the forum to view the eBook, but it's free. Here's the direct link to the transmission diagnostic routine once you join:

Jag-lovers' Ebooks


Please keep us informed, and if you manage to clear the PAD warning, check the VCM again for any stored Diagnostic Trouble Codes.

Cheers,

Don

 

i will probably just bypass the PAD sensor to get rid of the code.. i visually check my brakes all the time anyways....

there is ZERO corrosion on all relays, they all look brand new, they have been tested as well (i was surprised myself.)..

....so apparently this car was garage kept before i owned it.

if there was an issue with the fuse box to the TCM or a cold solder in that realm wouldn't there be fuse fault light?

and that damn rotary switch... i will attempt to open her up.

no worries i will keep yinz informed

 

Absolutely NOT!

In some cases (my own, for example) fuse boxes can look pristine and undisturbed - however, judging a book by it's cover rule comes into play here ...

Both of my footwell fuse boxes were faulty and caused my heater to fail.

The first winter in the car was a trip to the arctic on steroids - folks on the forum here suggested the fuse boxes, but after taking them out and having a look, they were so clean and perfect looking that I refused to believe they were the problem -plus- I had continuity across the front panel so I wasn't convinced..

Of course later, after exhausting all other possibilities I re-examined the fuse boxes, (this time with my glasses on) and found cracked joints at the back circuit board, easily solved BTW by simply re-flowing all the joints.

Both boxes had cracked solder joints. After the re-flow, everything worked once again. The problem with "testing" the fuse boxes is that a continuity check has to be made THROUGH the boards to the rear harness plug and not across the front terminals.

HTH

Larry

 

Hi Marco,

All three of our fuse boxes had cold solder joints. You're looking for dull joints with a "frosted" look, cracks, holes, separation from the wire lead of the electronic component, etc. When in doubt, do as Larry says and reflow the solder on every joint you can reach. Here's a photo showing the bad joints on one of the circuit boards:



Please do check out the diagnostic routine in the XJ40 eBook at Jag-Lovers. It will help you understand all the possible causes of your LHM and rule them out one by one.

Cheers,

Don