Hi guys, hope everyone is doing well!

The dash Trunk Open light in my 2005 S-Type 4.2 will not turn off. I looked around on the forum and YouTube and found a suggestion to spray white lithium into the switch as a first attempt but that didn't work. I also read somewhere here that most likely the issue is with one of the sensors in the back.

Unfortunately, I no longer have a Jaguar mechanic in my area, so I'm stuck with mechanics that specialize in European cars, but not Jaguar specifically. I took the car to one of them who had done the brakes on my RRS and this is what they came back with:

TECHNICIAN HAS BYPASSED THE TRUNK LIGHT SWITCH AND FOUND THAT THE LIGHT STILL STAYS ON.
CHECKED THE GROUND SUPPLY TO THE SWITCH - OKAY.
THERE IS AN OPEN CIRCUIT BETWEEN THE TRUNK SWITCH AND REAR ELECTRONICS MODULE.
2 HOURS OF DIAGNOSTIC TIME IS NEEDED TO GO FURTHER WITH THIS AT $148 PER HOUR.
QUOTE FOR DIAGNOSTIC TIME TO START ON THIS:
TOTAL $326.23 (OUT THE DOOR PRICE INCLUDES SHOP FEE AND TAX)
Labor: $296.00 Parts: $0.00 Sublet:$0.00 Subtotal: $296.00

I declined the work because I asked if they had the OEM Jaguar diagnostics scan tool and they said no. But the shop manager assured me that their tool is capable of reading all error codes in the car. For some reason I didn't feel confident that is the case so I told him I would come back here and ask some questions and get back to him.

Questions for you guys

• I have the Jag scan tool and cable. I just have to go through the process of installing it on a laptop (have to do the whole thing from scratch: WinXP virtual machine, scan tool, etc.), Should I go through that trouble or should I believe what the shop manager said about their ability to read all codes?
• I asked the shop manager if besides the switch, they checked the sensor. He said the switch and the sensor are the same thing. I remember someone here commenting on a thread that there's more than one sensor in the back that could cause the light to stay on (I may be wrong). Any thoughts on this are much appreciated.

Thanks in advance for your help!

Jose

 

As Douglas Adams would say, "Don't Panic!" I doubt you will need any fancy diagnostics to figure this out. It's a very simple circuit that controls the warning message.

The 'trunk ajar' switch is a simple on/off switch, part of the trunk latch assembly. See figure 12.1 here, near the lower right corner:

http://www.jagrepair.com/images/Auto...cal-2005on.pdf


The Rear Electronic Module (REM) is looking for a ground through the switch. Is the latch assembly part of the trunk lid, or is it part of the fixed body below the trunk lid? If part of the trunk lid, I'm willing to bet large sums of your money that the wire between the two points has broken where it flexes at the hinge point. You won't need a fancy scanner to determine this. Simply disconnect the latch and REM, and check for continuity through that wire.

If good, check the ground from the latch assembly, too. I'm not sure where that wire is grounded. The ground wire may also run back past the hinge. But it's also the same ground for the latch release, so if the electric release function works, the ground wire is good.

 

Forgot to mention something: While checking that wire for continuity, shake the harness while watching the meter.

Also had another idea, but am not sure this will work on an R model. Don't they have extra bracing where the rear seats fold forward? The same switch that controls the warning message also turns the light on/off inside the trunk. If the seats fold forward and you can access the trunk from the main cabin, close the trunk lid and observe the interior light. It should be off with the trunk lid closed. You won't even need a meter for this preliminary troubleshooting. Just shake the harness and see if the light turns on. If so, you've found the problem area. Pay close attention to where the harness flexes at the hinge point. You'll want to remove any trim panels ahead of time for access.

 

i had the same problem on my 06 str...trunk latched fine but still had the warning....replaced the latch and all was fixed...there is a very slight possibility that the rem is at fault, but i doubt it...the latch replacement is easy once the plastic cover is removed

 

Thank you guys! @kr98664 I'm not sure what you mean by is the switch part of the trunk latch assembly. This is what mine looks like. And definitely, the trunk light stays on. I don't have an R, just a 4.2, but I do have the folding rear seats so I was able to test as you recommended.





Thanks for your help!

Jose

 

The latch has the switch made into it. That is same as mine. That plastic cover comes off to expose the latch. Held on by tabs i think. Push in and pull. To access the latch bolts you have to take off the trim. There are a couple hidden bolts. When the trim is removed you can access the latch. Pay attention to the latch oreintation and the cable that goes to the key cylinder

 

Also had another idea, but am not sure this will work on an R model. Don't they have extra bracing where the rear seats fold forward

yes there is a steel plate across the back with a ski holder hatch. Otherwise no access. I have removed mine and love it. Just some nuts and bolts. The hatch has a built in bag for wet skis.

 

Hi guys, hope it's ok to revive this old thread. I'm sill having the issue. Here's the latest:

I ordered a new OEM latch from the dealer (freaking expensive!) an replaced it. It wasn't the latch. I took it to a Jaguar mechanic who first said it was "the module" in the trunk (maybe the REM) and that he ordered a replacement from eBay. He replaced it and it wasn't that. He said that it was "the other module" but I didn't let him order it as I don't want to go around blindly.

@kr98664 , do you have a part number for the harness? I couldn't decipher fig12.1. am not mechanically savvy, but I'm not scared either. I just need a little coaching :-)

Thanks in advance for your help!

Jose

 

Has the wiring been checked? Especially the harness where it flexes as the boot (trunk) is opened & closed.

Also, the latch should be easy to fool, if needs be by disconnecting and shorting appropriate pins.

On the bracing etc - you can probably fold enough of the rear seat (ski part?) to see into the boot from the rear seat & do the test that was posted some time ago.

 

Hi @JagV8 ,

I don't know how to check the wiring. I asked for the part number in my last post so I can see what it looks like to be able to check it.

The latch is good. As I mentioned, I bought a new one and that didn't solve the problem.

Sorry I forgot to mention the back seat test! I had done it and the light in the trunk was staying on. The mechanic that replaced the module said that fixed the issue, but I never checked it after. I just went outside and tested it and not so. I put the driver's rear seat down and locked the car. The light is still on almost 15 minutes later.

Jose

 

Are you having a shop do the work for you? Sounds like it, but am not sure. The wiring checks are pretty simple. We can walk you some very specific tests, but that won't be needed if a shop is doing it. Any competent auto electric shop can handle it. A Jaguar specialist is not required. There's a switch that provides a ground signal to the REM. When the REM thinks the trunk is not latched, it turns on the message on the dash, and lights inside the trunk. When the REM thinks the trunks is properly latched, it turns off the message and lights.

With the trunk open, you should be able to actuate the latch with a screwdriver or similar tool.

No idea on a harness part number. If you find the harness damaged, it's perfectly fine to repair it. If a wire broke, the most likely location is where the harness flexes at the hinge point. Carefully cut open the harness a few inches on either side of the bad spot. Splice in a new section of wire, locating the splices several inches away from the flex area. You don't want to put a splice where the harness flexes.


No guarantee the switch in your new latch is good. It's rare, but sometimes brand new parts are bad right out of the box. Test it to be sure.

 

Did you ever check the wiring where it bends going into the trunk lid as suggested up thread?
Might be a simple broken wire?
.
.
.