I noticed today that the RH tail light group is slightly brighter than the LH group. Ground corrosion? I previously cleaned up the grounds behind the head lights. Any other locations to look at?

 

According to the wiring diagram, the tail lamps all go through the rear electronics module for both power and ground, which is located in the right rear of the car. The ground point for the module should be close by.

Dave

 

Dan R;
I have a similar issue which seems to be the result of low voltage on the power out from the rear body control module. I'm curious to follow what you learn from your specific problem. My lights work, just at lower intensity.

William

 

Ground/earth points in the boot/trunk area are shown in the Electrical Guide which can be

downloaded from a sticky on this forum.

 

Hi Dan,

Your problem could be as simple as corrosion on or looseness of an electrical connector.

All the rear lights are grounded through the Rear Electronic Module (REM), which is behind the right-hand carpeted trim panel in the trunk. To remove the panel, remove the two Torx screws in the tie-down hooks/hinges of the floor panel and temporarily remove the floor panel. Remove two or three plastic fir-tree press rivets - I can think of one near the tail lamp and one that goes up into the right end of the forward roof of the trunk, below the backlight/rear windscreen. You can then pull the trim panel out, beginning at the forward end and working your way back. The top edge of the panel just slips down from under the weather strip.

The REM is on the right rear inner fender, and all five of its ground circuits connect at the ground stud on the inner wheel arch just forward of the REM. Aluminum-oxide corrosion appears as a thin, white, powdery coating that looks innocuous but is an electrical insulator. Clean it away with a small brass-bristle brush and zero-residue electronic cleaner. The torque spec on the ground nut is just 6.5 ft. lbs., or just a little more than hand tight. Several members have learned the hard way how easy it is to snap the ground stud off the body by overtightening the nut.

Each of the tail lamps receives ignition-switched power from various fuses in the Rear Power Distribution Fuse Box (RPDFB), so if cleaning the ground doesn't work, you'll need to measure the supply voltage to each lamp group and trace the circuit until you locate the problem. Faults in the RPDFB internal circuit boards are known.

You can download the Electrical Guide here:

Jaguar X350 Electrical Guide 2005

Cheers,

Don

 

Don B; Thank you for your guidance above.

At the risk of hijacking this thread.........
I have an 04 xjr, 87 kmi that I have a similar issue (tail lamp intensity) and have eliminated REM grounding as the problem. I believe my battery is good. I'm seeing an intermittent voltage drop (14.3V to 12V) at the RPDFB fuse (F46) for my Rear RH Turn lamp when activated. Fuse voltage (F46) drops to ~7V when the reverse lamp is activated. These lamps and my inoperative seat heaters are all fed power from RPDFB PCB relay #5 (Electrical Guide fig 1.7, 8.3, 11.7). The high mounted Stop Lamp is also powered from relay #5 but is shown to be LED (low current).

1) How do I troubleshoot this RPDFB PCB relay?
2) Can the PCB be replaced or do I need to replace the entire RPDFB?
3) Power to the seat heaters is routed and switched through the FEM. I don't see how the switched seat heaters could be loading down the circuit when not in use. Do you agree?

Thank you for your experience and your time.
Best Regards, William

 

Hi William,

I just took a quick look at the schematic and it's interesting that "Switched System Relay 5" is also "Relay 8 (R8)." Go figure.

Since this "Non-serviceable PCB relay" can't be conveniently accessed directly, you could test for similar intermittent voltage drops at the other fuses it powers in addition to F46: F47, F48 and F49. The relay receives its power from the RPDFB power bus. If you don't see a similar voltage drop through the other fuses, that may suggest your thoughts about the problem being on the load side are worth pursuing.

It is possible the PCB relays could be replaced if you can find suitable replacements and have the necessary soldering skills, but Jaguar's solution is to replace the RPDFB.

Note the explanations of how the REM controls the rear lighting in the left column of pdf page 90.

I have to run, but just noticed that the Orange/Green wire connects both reverse lamps to the Parking Aid Module. This probably tells the PAM the the transmission is in Reverse so it will activate the rear parking aid sensors. Have you noticed any unusual behavior in the Parking Assist? There is a splice CRS36 somewhere in the harness but its location is not given.

I'll check back later.

Cheers,

Don

 

First thing is the tail lights are positive ground not negative.

Power to the lights is supplied of pins 1 and 7
The Rem provides a switched ground.

First things to check is the REM Ground post
The best way to do this is to remove the REM plug and test the resistance of the earth pins to the body

Next check the tail lamp harness.
With the power plug still off the REM, remove the plugs from the tail lamps.
Check the voltages on Pins 1 and 7 of both taill lamps.

If you get a significant difference chase down that circuit

Assuming thats OK check the tail lamp.
Supply power to pins 1 & 7. Then ground the remaining pins one at a time. Check if the lamps are the same or not.

Next check the harness
With the power plug still off the REM, check the resistance of each of the pins. You are measuring between the REM connector and the tail lamp connector. You should get close to no resistance.

With all that done the only thing left is the rem itself

Cheers
34by151

 

Don B and 34by151; Thank you. I'm working through your suggestions; here's what I know thus far:

(1) REM grounds: CR11-11, 12, 25, 26, CR71-15 all measure 0.2 ohm from REM connector to chassis ( Good ! )
(2) other RPDFB, PCB relay #5 fuses: have not checked these yet
(3) Orange/Green wire (CRS36 splice) the PAS is inoperative throwing codes C1742 (rear sounder circuit fail), C1703 (RR corner sensor failure). I have not checked the parcel shelf PAS speaker yet. the RR corner sensor is clicking normally.

Question for 34by151:
"Next check the tail lamp harness.
With the power plug still off the REM, remove the plugs from the tail lamps"
Are you referring to the CR4 B+ pwr to the REM -or- CR71 from the tail lamp assembly?

Best Regards, William

 

Both, you need to test the resistance of the harness

If you find a much higher resistance from the dull light side you have a harness issue.
Clean up the pins and retest. If you get the same result replace the wire.

Cheeers
34by151