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UK XLR, one of the few..


Mar 3, 2021
As per my intro post I expect to shortly (subject to customer approval) be diagnosing and hopefully fixing, one of the only 3 XLR's in the country.

She's in lovely condition, low mileage, 04 model, but with the frequently mentioned issues of boot err.. trunk not opening, roof not working and occasional "service suspension" message.
I have only had a cursory look at it, however it also has what appears to be an intermittent complete shutdown of the high speed CAN network (!) -looking at a plethora of U codes (lack of module communication) on the scanner.
I suspect - but have not yet verified that this is all linked to the rather damp modules and wiring in the trunk as the RTD suspension module is on the HS CAN network.
When I got to it both the RTD (suspension) and FTC (roof) modules and wiring were pulled out and there is evidence of "intervention" and much wetness.

None of the UK data suppliers have any information but Mitchells got straight back to me and have confirmed that I can get access to wiring and service info through them.

My Autel scanner gives me access to all the data PIDs for the roof so as long as I can get the switch matrix for that, I should be able to figure out where the issue is - that and the Top Hydraulics video walk through!
I have seen two different diagrams for the CAN topology so will be interested to see what Mitchell has.

Should be interesting and I hope for the owners sake it does not need any new modules.

Right, need a cup of tea now..
I have been taking a good look at the long list of codes set by the network shutdown and I have two questions.

First, is this topology correct as it differs from the one in the XLR systems book ?

@ ID_Fig2X_GM_Topology[1].jpg

I see the BCM is the Gateway and also has a terminating resistor, I read elsewhere that the 2nd resistor is in the ECM.

Second, following the shutdown I had a mountain of U codes (Autel 906BT) and as far as I can see the everything except the ESC (suspension module) on the HS network was complaining about lost comms with each other. Everything on the Class 2 network was complaining about loss of comms with everything except the ESC on the HS network. In fact the ESC was suspiciously absent from the DTC's as if it was not on the network.
The ESC is the no.1 suspect by location and moisture, but if it died and took the network down, why did the other modules not set a U code for it missing and if it was alive why did it not set any codes about lost contact with the other modules?
Seem unlikely that it does not at least have a heartbeat on the network. I feel I am missing something - it may be a scan tool error of course.
Any input welcome!
Hi and welcome!
You will probably need to invest in a 'Tech II' scanner. As best as I understand, it was designed for this system and the only one that can really do the job for you. There are lots of threads in here regarding originals versus clones, some with successful results with the latter, others...not so.

I would have thought the folding top module (FTM) would have been most suspect due to location but I guess depending just how things managed to get wet in that area (common issue) the ESC may have somehow suffered worse.

I believe TopHydraulics can repair the FTM. ESCs....ouch. I have heard that the '04 and '05 are not compatible with later years, therefore it is supply and demand and the price gougers will do you no favours. :(

If you don't already, the original service manuals are available. Costly, but available, and chalked full of diagnostic information - and reading for months.


Gord :thumbsup
Thanks for the welcome Gord.

The FTM is not on the HS CAN network so it may well be the issue for the folding top but it would not be the issue with the intermittent CAN network shutdown.
I may need to borrow a Tech 2 for a top re-learn or the Autel might do it. So far I have full access to all of the modules and all of the top position sensors, as well as bi-directional control of the pump solenoids, but won't know until I get properly in to it.

I'll get my oscilloscope on the CAN lines and do some wiggling and unplugging. Hopefully I will see a degraded CAN signal from the start - though it is an intermittent problem often the 'scope will show that things have started to go bad, just not enough bad to trigger a shutdown.

If it is the ESC module then I have a plan involving new shocks and building a CAN signal spoofer that should keep the dash message quiet. - Assuming I can get the data I need to do that. But I am getting ahead of things here, it might just be corrosion or a short on the CAN lines, or it might be nothing to do with the ESC.
I can buy access to Mitchell for the wiring and service info for $30/year Do it Yourself Automobile Repair Manuals - Mitchell 1 DIY - Once I get the job of course !
Just a quick update on this, I got the job and have been focused on getting the trunk to open and the top to run.
The Mitchell data I mentioned above is brilliant for the top and electrics. Not looked at anything else on there but for the money I'd say you can't go wrong really.
Took a while to figure out that the trunk hydraulics are controlled directly by the BCM without the FTM when its a trunk operation, but the same trunk hydraulics are controlled by the FTM when its part of the top operation.
Progress has been made in repairing corroded wires, replacing fuses and a microswitch, and unsticking relays. Top now faults at the header latch switch not showing as unlatched when it should (microswitch), also both tonneaus are out of spec on the potentiometers.
For your interest this is the top closed with the readings from the Autel - where the value is given as "middle" - it should not be! (note that items 6 and 2 were also faulty, that's been fixed)

Top closed faults.png

One big bonus is that this information is put out on the Class 2 network by the FTM - so there is an increasing chance that it survived it's swimming lesson.

However, I am expecting that when I get to it next I will find that the pump electronics may not have survived, from the failure mode I suspect solenoid one and possibly the motor itself is bad - drawing 3.5A at a standstill is bad news..

Definitely time for tea...
Pump out, motor is locked solid.
Remove motor from pump. Clean up oil.... Motor is new, motor off pump works fine.
Pretty sure pump has been re-assembled wrong, can see the bearing is not in square for a start, trying to find an exploded view or a pic of how it goes together.
With the alternative of an expensive trip to TH and back in agreement with the client I bought a SAAB 9-3 pump and re-built the XLR one from that as they are very similar. Works great.
Now that all works I come to find that my Autel does everything the Tech2 does... except a top re-learn. I expected top be able to rent Tech2win from ACDelcoTDS but the site has been "unknown error" for days. So at the moment stuck for a re-learn.
Spreadsheet time to calculate resistor bypass... possibly..
Hmm yea, tried that. Then looked at it in a spreadsheet, series and parallel, both legs. Still could not make it work. But I may be being thick so very open to suggestions.
Front Tonneau
Pot res 14.4K
Closed = 7.7k = 132 counts need 123
Open = 5.8k = 163 counts need 159 so thats OK

I can get either the Closed or Open in spec, just not both. I was using larger resistance
My assumption is that it measures the voltage centre to +ve so I am calculating 5v less the drop x (5v/255)
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No still on the top as I needed to get a used pump and re-build the one that was in there.
I did the mod for the Stabilitrack TSB.
The car went into a limbo state between acc and ign, whilst working on the top, the whole CAN bus was down. I split at the ESP plug and the issue is on the ECU side. Unfortunately next day it was back to almost normal though something was pulling down the dominant voltage on the CAN network even when split to 1.7v. Following day completely normal, so can't get further with that until it's broken again.
Also I need to get the top working so the client has something to show for the money, but I am completely stuck at a top re-learn as the ACdelcotds site is down.
ACDelco site back up. Tech2Win according to it's manual - needs a PDU API enabled J2534 box ie DoIP. So software from the 90's needs the latest diagnostic tech to work. Bangs head against virtual wall and gets out credit card.. grrr...
Yes I could buy a VX nano wotsit but I'll unlikely see another GM car and I don't use clones on customer cars, so I might as well spend on something useful.
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So after extensive testing, and getting no response from either the top or the trunk I finally gave in and said to order a new FTM. This took a long while to order and arrive and here we are 4 months later with it installed. The trunk now works, my re-built from parts pump works, but the top just ignores all requests from Tech2Win to re-calibrate. Put it in "learn" press the button and it just says "top not secure" - which is because it needs calibration.
Been through all the calibration pre-requisites and just no response to the switch (other than showing as pressed in the scan tool).
Driving me nuts this one!
Update on this, I manually adjusted the pot/sensor for the rear tonneau which put everything in calibration when closed. This enabled the top to start the sequence in learn mode, but it stopped and the FTM lost all communications at the point of retracting.
Went back into the trunk and found an intermittent bad earth, on the earth wires going directly to the solenoids. Traced this to a corroded in-line plug/socket, which also contained a sensor wire connection.
Now I can get the top to go all the way to un-stowing the rear tonneau - then it stops with it halfway out as I had the pot manually adjusted it already thinks it has finished.
Manually stowed it closed now the calibration fails at trunk lift - works fine from the trunk button so not sure what is going on there.
So almost there ! Must be yet another corroded wire/dodgy connection.
curious how you adjusted the sensor manually? there is just one screw in it and the plastic drive. There is really no adjustment on it. IF you have any movement on it thats maybe your problem. It has to be read and calibrated with the tech 2.
Removed the bolt and twisted it until it was showing Open, not Middle. Secured with zip-tie. Neither calibration/learn or operation will start with any of the pots showing "middle". - I assume this is wrong and that calibration should ignore the settings and set new ones - but it does not - at least not with Tech2Win or the Autel that I have.
None of the learned values are retained after the part calibration.
That was the only way to get any movement at all from the system, rotating it, but keeping it so that it would be adjusted by the action of the tonneau opening. The top will not operate at all if one of the pots is between open and closed counts.
Hoping that by running it through a complete cycle I could use the system tolerance to adjust it a bit at a time so that it could be re-learnt to the correct points.
I am assuming it is an issue with T2Win or the comms hardware I have. It can't be designed like this !
I can tell you if the screw that fits the hole in the position senor gets loose it can cause the top to stop working by just 3-5 clicks of movement. Once tight you have to do a relearn. You are just guessing and Spending time , I hope your customer appreciates all your efforts but you need to find someone in the area with a tech 2 and you can find out what you need in about 5 minutes
I have all of the information, I also have Tech2Win working, I have tried to get the top to re-learn but it will not, everything proceeds through the learning operation but neither system will ignore the current status. There are no DTC's all power and comms issues appear to have been resolved. The issue appears to be with Tech2win or the comms hardware. I am trying to find a GM enabled Tech2 but it's an aincient tool for cars we don't have over here!
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