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I've had an ongoing issue that has my GM XLR-Certified Master Technician mystified. I have an 05 XLR 30K miles that randomly displays the "Service Engine Soon" light in the DIC when I start it. This weekend it came on and I went directly to the dealership, message displaying in the dash. trouble is there are no codes whatsoever in any of the computers. I was told that for a message to display a code needs to activate it, but not in this car... This has been continually happening for several months, but no codes. Has anybody seen this before, or are there any ideas? My tech is stumped.
 

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Sticky and non-sticky.....

I've had an ongoing issue that has my GM XLR-Certified Master Technician mystified. I have an 05 XLR 30K miles that randomly displays the "Service Engine Soon" light in the DIC when I start it. This weekend it came on and I went directly to the dealership, message displaying in the dash. trouble is there are no codes whatsoever in any of the computers. I was told that for a message to display a code needs to activate it, but not in this car... This has been continually happening for several months, but no codes. Has anybody seen this before, or are there any ideas? My tech is stumped.
I work with marine applications of the "Kavassor Kan Kingdom" systems, similar to those used within our cars. As to the 'fault status', an inoperative O2 sensor would creat a 'sticky fault', but a sudden dip in voltage or current would not. That short burst of low power is considered a 'non-sticky fault'. Also that sudden burst of low power may trigger the exact problem you describe. A low power/intermitent (shorted plate) battery, or a loose battery cable connection may be your only mechanical problem. While cranking the motor many electronic systems are 'waking up' and that also takes power. Each of the electronics systems in the car has it's own "power stabilizer" built into that component, to ward off overpowering and UNDERPOWERING the fragile 5V DC electronics. Starter, solinoid, fuel injectors, fuel pumps, spark/coils/ignition, engine ECM and on down the line, all take at least 11 V and good steady current flow from + to - or in the actual physical action electrons going from - to +. Check all your main power cable connections and swap batteries for a few 'test days'. Good luck.
 

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We batted this around in another venue and the general consensus is since the message is generated by the ECM and sent to the BCM for display, both are suspect, with the BCM being 51% more so. The dealers are loathe to replace (expensive) components that aren't specifically called out by Diagnostic Trouble Codes, and swapping (--components, that is!) is frowned upon, so it's a tough call. This issue isn't common, but several owners have reported the same symptoms. A BCM replacement fixed one of them.

Filtering circuits in digital system's power supplies are supposed to deal with transients, but all it takes is a little EMI to make a digital bus go apesXXX. Aging components, microscopic etch flaws in vibrating environments, weak solder joints, etc all add up, making troubleshooting integrated systems that don't display fault codes a job for knowlegeable techs who really understand how a circuit is supposed to work when standard troubleshooting flows don't apply. These kinds of faults seperate the good techs from the great (and/or lucky) techs.

Anybody else out there have any similar problems/fixes?

CC :cheers
 

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Discussion Starter #5
Great info. the battery was replaced several months ago when the original failed. That left a bunch of codes in history that have been cleared two visits back. I'll check the cables just to be sure. This is its 8t visit and several repairs later to clear the this message. I work with computer and know how they can have quirky failures, so I'm leaning towards one of the modules. Consensus is the BCM. I can order the part from GM, only $264 and it can be removed and replace with 3 screws and 2 connectors according to the service manual. The catch is, it then has to be programmed with the VIN number using the GM Tech tool, once again eliminating the home mechanic from doing repairs. Also have to clear any codes set by the initialization. I'm waiting for the dealer's estimate, they keep talking about how expensive the repair is... other than the reprogramming it's a simple job. This is frustrating on many levels, putting a damper on my love affair with the XLR.
 

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You're right. DIY-wise, you're totally dependent on a dealer to perform routine troubleshooting tasks with a Tech 2. Labor-wise, they shouldn't soak you (as opposed to won't soak you) since BCM replacement/programming is pretty easy. Maybe twenty minutes to remove/replace, and ten to load the new numbers and run a full diagnostic. Clearing stored codes is one keypad press. It isn't rocket science, --but then, you're not supposed to know that. See if you can get a realistic labor estimate from the Service Advisor by explainng the replacement process in the Service Manual. Their labor books are pretty realistic, unless they're cross-eyed and dyslexic, and then any number may appear. This way, they can't try to snow you by pretending the whole repair process is mysterious/expensive or hide behind their dyslexia.

One way to save a few bucks is buy the BCM yourself (saving around 40% in the process) and have the dealer install it. Mine wouldn't warranty the (OEM) parts I bought online, but would warranty their labor, so it worked out. After a couple of cycles of that, I sprung for a Tech 2 and haven't been back since. (Of course, the car knows I'm armed and hasn't had any real issues either!)

:cheers CC
 

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Maybe i should buy a Tech 2 and she'll behave :jester

Thanks for the advice, I've called for estimate and made it clear I'm not happy with 8 trips to the dealer, maybe they'll play nice. If the Service advisor quotes to high, I'll move up the chain of command. The only problem I have is that it's the only dealer nearby with an XLR-certified tech.

Thanks to all who posted some advice, here's to you :cheers

I'll keep you posted
 

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So you are sure.......?

We batted this around in another venue and the general consensus is since the message is generated by the ECM and sent to the BCM for display, both are suspect, with the BCM being 51% more so. The dealers are loathe to replace (expensive) components that aren't specifically called out by Diagnostic Trouble Codes, and swapping (--components, that is!) is frowned upon, so it's a tough call. This issue isn't common, but several owners have reported the same symptoms. A BCM replacement fixed one of them.

Filtering circuits in digital system's power supplies are supposed to deal with transients, but all it takes is a little EMI to make a digital bus go apesXXX. Aging components, microscopic etch flaws in vibrating environments, weak solder joints, etc all add up, making troubleshooting integrated systems that don't display fault codes a job for knowlegeable techs who really understand how a circuit is supposed to work when standard troubleshooting flows don't apply. These kinds of faults seperate the good techs from the great (and/or lucky) techs.

Anybody else out there have any similar problems/fixes?

CC :cheers
You are sure that this problem is from within the ECM or BCM ? No small 'split second event' anywhere thruout the 'can network' could effect the ECM in this way ? I'm finding it hard to understand how a BCM internal problem would not 'throw any codes' when the ECM is still operating the car/motor in normal fashion. First of all, it happens "at start up", I read nothing about any other operational activity. Second, the "Service Engine Soon" warning is directed to 'engine only questions' and not 'body' or 'accessory' related. The ECM (as I have quickly read on line) is the 'king' of this vehicle's 'domain' and has 'rule' over the BCM. (right ?) This means that IF the BCM WANTED to DO ANYTHING, the ECM would be required to allow the BCM to do that action. The ECM sends a signal to the BCM, put the "SES lamp" on. The BCM reads that signal, sends a reply 'yes I put on the "SES lamp" (in English or other) right now. The ECM would reply 'OK' handshake. "Signal sent, reply/action, handshake". IF the BCM (were malfunctioning) sent/action "SES lamp", the lamp would come on, the reply back to the ECM would be sent at the same time and the ECM would NOT OK HANDSHAKE, it would throw a code. Because the ECM didn't send any signal for any action/reply to the BCM. IMHO, the ECM can and will operate without the BCM functions operational, but the BCM cannot function without the ECM. Correct ? I offered the above insite because I know that the "GM and Mercury Marine" can systems are almost identical in structure and software. GM designed both/all of these systems. Along with the fact that I have found this problem in the Mercury Marine DTS systems. (fly by wire) It's a long story, but it did take over 75 hours of testing (3 months) of "one change/test" at a time.
 

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"The ECM (as I have quickly read on line) is the 'king' of this vehicle's 'domain' and has 'rule' over the BCM. (right ?) "

The BCM is the gateway between the GMLAN and Class 2 bus. One of its (many) functions is to emulate all of the high-speed GMLAN modules on the Class 2 serial data circuit. It transmits multiple Node Alive messages using source IDs that reflect each GMLAN node, which includes the ECM. The ECM monitors all engine-related sensors, performs diagnostic checks, and alerts the driver by illuminating the Multi-Function Indicator Lamp, (MIL) while setting a Diagnostic Trouble Code (DTC.) The MIL command is passed to the BCM via GMLAN, then placed on the Class 2 bus for the Instrument Panel Cluster (IPC) to display. --This is the nominal path.

The BCM only responds to commands (data request/acknowledge/DTC/Health & Status) in this regard. (It deals with power distribution control too, but that isn't the issue here.) There is no King, per se. Just data packets gathered by controllers monitoring specific functions and passing them to the BCM for display on another bus. While this architecture uses the CAN, (Controller Area Network) it also has to work in tandem with the slower Class 2 bus, on which the BCM serves as an arbitrator.

In complex digital systems, there are soft faults, (produced by glitches and timing errors and are usually intermittent) hard faults, (that set codes and can be more easily resolved) and system anomalies (persistent/un-resolvable and cause no system degradation, --just operator annoyance.)

In this case, with an illuminated MIL and no DTC, a system tech needs to look at the operating parameters of the engine to ensure its within specs to determine whether the ECM is seeing a potential fault or flagging the bus with a non-existant error. A sensor on the very ragged edge could conceivably trigger the ECM's diagnostic parameters without setting a DTC, but I think this car is pretty well engineered (diagnostics-wise) and since the vette electronic systems shares so many similarities, (They even share the same module IDs on their respective GMLAN and Class 2 buses.) bad parameters would be more evident on the combined production of both vehicles, --especially with the larger number of vette's produced. Being a distant cousin has some benefits. Glitches found on the higher-production vettes may trickle down as future firmware updates for us.

The ECM and BCM are both suspect. Come to think of it, the the IPC could be erroneously turning on the MIL; weirder things have happened. Since I've heard of the BCM fixing the problem with the same symptoms, I'd give it a 1% differental between the two (ECM/BCM.) Of course, this is all speculative on my part. I'm just some knucklehead, sitting around in my boxers, swilling beer when I should be in bed, sleeping fast for my day job. I'm not sitting in the car with a Tech 2 plugged in to see for myself. If the problem gets resolved and we get feedback, then we'll know for sure, and can place the fix in the knowledge base and our collective noodles.


:cheers CC
 

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Discussion Starter #11
Just a clarification based on AzGeo's comments. The message is Service Vehicle Soon in the DIC, not Service Engine Soon, and there is no engine light. That basically eliminates some of the engine operations and emissions systems as the culprit according to my dealer's technician. He also told me, though the message appears at start up, that doesn't necessarily mean the code was not set previously. Apparently some messages appear immediately and others don't? I'm not a mechanic but that seems strange to me, however it was the case back when I was having mass air flow issues earlier in my ownership. Then again there are no codes being set in this instance, so who knows what this car is thinking. It's been two days since I heard from the technician or my service rep, so that may not be a good sign.
 

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Just a clarification based on AzGeo's comments. The message is Service Vehicle Soon in the DIC, not Service Engine Soon, Thank you, I stand corrected. However, I do (now) understand your terms, such as "GMLAN" or "Class 2 Bus". We have different names for the "Bus circuits" but it is the same basic system. (GM designed) When I mentioned "King" refering to the ECM, I was speaking about the overall control it has over the entire system/vehicle. Redundancy and self diagnosis are the key factors within all of the ' classes of Bus systems'. Since all of the different components of this multiplexed system run on the same 'speed and signal language', the different levels of systems do speak to one another all the time. The BCM feeds info to the ECM as it is programed to do, and the ECM 'looks at all the functions of the engine and body' constantly. With an operational ECM, but a non-operationl BCM the car will start and run. But, if the BCM is functioning and the ECM is not, the car will not run. The ECM can also transmit incoming data/responce on any bus and transfer that data to another bus. The ECM can also search thru all the bus systems to find 'missing data' from a malfunctioning bus circuit. Redundancy. Also the BCM gets it's 'wake up' from the ECM turning on the main power relay (s). I'll bet the throttle activation is part of the 'class 1 bus', but has an override built into the 'class 2 bus' (in the stop lamp or cruise control off circuits) Redundancy for partial failures too. We have only 4 levels of 'bus class' in the marine side, does this car go on with other 'bus class' levels ? (5/6/7.....)
 

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AzGeo,

XLR has two distinct buses tied together by the BCM. A failure in either the BCM or ECM can prevent ignition. The Distance Sensing Cruise Control module/Engine Control/Transmission Control/Electronic Brake Control modules are tied into the high-speed GMLAN bus due to their critical time-sensitive, integrated functions.

If the DSCC module see a target within it's range gap, it places a "Warning Will Robinson!" message on the bus. This would qualify as a top priority flag. The TCM may downshift, the TCM may slow the engine revs and and the brakes may be applied, depending on range rate (opening or closing) and distance to the target.

One of the few redundancies within the network is the BCM. If the RCDLR fails (can't see a fob to let the BCM know it's time to start the car) the limp-home antenna is wired to the BCM.

The ECM doesn't look at body functions, it just processes engine-related sensor data and accepts throttle control commands.

All kinds of data is placed on the network for any module that needs it. Ambient air temp sensor data may be required for the HVAC module to cool the car to a set level at ignition; if the cabin microphone noise level gets to a certain point, it's value will be factored into the noise compensation adjustment to the sound system --if that feature is enabled. If the window position count doesn't correspond to them being fully lowered when commanded, the Folding Top Control module won't permit the top to move. The list is mind-boggling.

One purpose of the BCM is to ensure both buses are getting messages back and forth to whatever module needs it. It monitors status and health from each module which is transmitted at regular intervals.

You're right, the ECM can transmit data to either bus, but it has to go through the BCM to do it. There is no Class 1 bus however. I'm sure you have other names in the marine world for the different buses used. For XLR, it's two: GMLAN and Class 2. Both are integrated into a Controller Area Network, which is why a CANDi module is required with a Tech 2. I hope I'm explaining this in a way that makes (some) sense.

:seeya CC
 

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Thank you !

AzGeo,

XLR has two distinct buses tied together by the BCM. A failure in either the BCM or ECM can prevent ignition. The Distance Sensing Cruise Control module/Engine Control/Transmission Control/Electronic Brake Control modules are tied into the high-speed GMLAN bus due to their critical time-sensitive, integrated functions.

If the DSCC module see a target within it's range gap, it places a "Warning Will Robinson!" message on the bus. This would qualify as a top priority flag. The TCM may downshift, the TCM may slow the engine revs and and the brakes may be applied, depending on range rate (opening or closing) and distance to the target.

One of the few redundancies within the network is the BCM. If the RCDLR fails (can't see a fob to let the BCM know it's time to start the car) the limp-home antenna is wired to the BCM.

The ECM doesn't look at body functions, it just processes engine-related sensor data and accepts throttle control commands.

All kinds of data is placed on the network for any module that needs it. Ambient air temp sensor data may be required for the HVAC module to cool the car to a set level at ignition; if the cabin microphone noise level gets to a certain point, it's value will be factored into the noise compensation adjustment to the sound system --if that feature is enabled. If the window position count doesn't correspond to them being fully lowered when commanded, the Folding Top Control module won't permit the top to move. The list is mind-boggling.

One purpose of the BCM is to ensure both buses are getting messages back and forth to whatever module needs it. It monitors status and health from each module which is transmitted at regular intervals.

You're right, the ECM can transmit data to either bus, but it has to go through the BCM to do it. There is no Class 1 bus however. I'm sure you have other names in the marine world for the different buses used. For XLR, it's two: GMLAN and Class 2. Both are integrated into a Controller Area Network, which is why a CANDi module is required with a Tech 2. I hope I'm explaining this in a way that makes (some) sense.

:seeya CC
I do thank you for some insite as to how this car works, but it seems to me that all of this still backs up what I have stated above. As you point out "the BCM is the junction box for all of the data (body function data) being processed on the line. Your "GMLAN" is just called "can one" in marine use. Let's try to simplify what is going on here. At the press of the GREEN LIGHT, the ECM TURNS ON THE MAIN POWER RELAY, correct ? This in turn turns on all the other BCMs and control modules within the car, right ? Did you know that we have 'joy stick controls' in our marine electronic systems ? These contols can actually PARK a twin engined boat at the dock without steering input ? Our cars are complicated, but the boats I work with use the same exact electronics and they are far from simple. YES, there are a great amount of electronics envolved in these cars, but taken 'ONE BY ONE' each system can be broken down to it's simple basic roots. "It's only 1's and 0's !"
 

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"At the press of the GREEN LIGHT, the ECM TURNS ON THE MAIN POWER RELAY, correct ?"

---No. Pull the toe board cover back on the passenger side. That is the BCM. It contains numerous relays and fuses (in addition to the UBEC under the hood.) The ECM only deals with the engine.


"This in turn turns on all the other BCMs and control modules within the car, right ?"

---No. There is only one BCM. and yes, primary power is applied to all modules at power-up.

"YES, there are a great amount of electronics envolved in these cars, but taken 'ONE BY ONE' each system can be broken down to it's simple basic roots. "It's only 1's and 0's !" "

---Absolutely! The old adage, "How do you eat an elephant?" "One bite at a time." certainly applies with integrated systems.

:cheers CC
 

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Discussion Starter #16
Another BIG difference between ECM vs BCM. The programming that controls the ECM can be flashed and updated by the Tech when necessary, and there have been some mandatory updates to the 2005. According to my Tech at Cadillac, that's the big problem with the BCM. It's programming is burned in, and not updateable; that's why it quickly becomes the culprit in investigations, and is only resolved by replacement. There was an issue years back when the BCM flooded the system with voltage fluctuation codes and the driver could not get the car in gear, a failsafe system in the program. Turning off and restarting with stop the flood of codes and the car would start. The only solution was to replace the BCM. Obviously not my problem, I get no codes; but that problem brought to light the fact that the BCMs programming could not be updated. Still waiting for a response from my Service Rep and Tech. Starting to get my pressure up, oh well :cheers
 

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I've had an ongoing issue that has my GM XLR-Certified Master Technician mystified. I have an 05 XLR 30K miles that randomly displays the "Service Engine Soon" light in the DIC when I start it. This weekend it came on and I went directly to the dealership, message displaying in the dash. trouble is there are no codes whatsoever in any of the computers. I was told that for a message to display a code needs to activate it, but not in this car... This has been continually happening for several months, but no codes. Has anybody seen this before, or are there any ideas? My tech is stumped.
There has been a lot of discussion on this, but you don't seem any closer to a solution.

A couple of questions:

1/ Do you have an actual text message telling you to get your XLR serviced, or is it the amber engine shaped light (called the Malfunction Indicator Lamp - MIL) that is on (or both)?

2/ Have you tried a different Tech-2?

The fact is that if you get that light you either have a fault code somewhere or you have a fault in the wiring. Are you sure you don't have U1000 or something?

The most common reason I know of for no fault codes (when there should be codes) is that they have been reset, usually through a power failure (i.e. a loose connection or similar).

If it is the MIL lamp that is on and no message, then a short to ground in the lamp wiring is indicated. There is a section in the workshop manual on that. Start with the index under 'MIL always on' and go from there.

I have a 2004 XLR, these notes are taken from that w/s manual.

As a summary, the opening move (after a basic check) is to disconnect the ECM. The MIL is an LED and is grounded by the ECM on C1-24. The good news is the signal passes through the underhood fuse block (don't know why), in my manual it comes in on C3-C2 and goes out on C2-F1.

If you have the service engine lamp lit (and it is down to a fault code), then it should be an emissions problem and that can be scanned by any old scan tool (isn't that the point of the standardised codes that came with OBD-II in 1996?).

BTW, if the MIL is flashing, the fault is serious and you should stop driving.
 

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Discussion Starter #18
The only message is the "Service Vehicle Soon" message in the DIC, the engine light does not come on, no codes in any of the memories, ECM, BCM, TCM. Had codes in the past, all were resolved an cleared with prior repairs. This is something new and produces no codes.

Don't know if my Dealer technician has tried another Tech2, but it works on all his other cars and repairs.

There are also no symptoms with the car. I'd just ignore it, but according to the manual the SVS message is serious and the car should be brought to the dealer. The message appears every couple of days or so when I turn on the car. Unfortunately the dealership wants nothing to d with the car unless the get a code. I've stopped by several times, with the message in the DIC and without the message, so far no codes. If I press reset, or restart the car the message goes away.
 

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The only message is the "Service Vehicle Soon" message in the DIC, the engine light does not come on, no codes in any of the memories, ECM, BCM, TCM. Had codes in the past, all were resolved an cleared with prior repairs. This is something new and produces no codes.

Don't know if my Dealer technician has tried another Tech2, but it works on all his other cars and repairs.

There are also no symptoms with the car. I'd just ignore it, but according to the manual the SVS message is serious and the car should be brought to the dealer. The message appears every couple of days or so when I turn on the car. Unfortunately the dealership wants nothing to d with the car unless the get a code. I've stopped by several times, with the message in the DIC and without the message, so far no codes. If I press reset, or restart the car the message goes away.
According to my 2004 w/s manual, "Service Vehicle Soon" on the DIC is raised by the ECM for a non-emissions related problem.

This means that you can get it for about three reasons I can think of:

1/ You have a non-emissions related fault code in the ECM
2/ You have a faulty IPC (i.e. it is making it up)
3/ You have some other problem.

Of these I lean towards 3/. Given you can't find any fault codes stored in the ECM, I am thinking you might be having power problems, either during crank or shortly afterwards (these could cause the ECM to erase a stored code).

1/ I would have the ECM connectors removed, cleaned with contact cleaner (DO NOT USE WD-40) and firmly push them back into place

2/ I would look really closely at the battery performance, including proper terminal cleanliness.

Put a data logger on the battery cables and measure voltage (not on the actual battery terminals), or perhaps measure voltage in the cigar lighter. Watch the voltage during crank. You really don't want to go much below 12v, maybe 11v. 9.5v is the absolute minimum, but a good battery should do better than that.

Can you confirm that when you switch off after driving, the odometer displays for around 20s?

I would then get your dealer to loan you an ECM. I don't understand why they refuse to diagnose an XLR arriving at their service center displaying the message that the ECM is reporting a non-emissions fault. Seems pretty basic to me.
 

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Thanks for the analysis. Had battery issues a while back, now its a new battery and I checked the terminals to ensure they are tight and clean. The tech did check the battery and voltage was great according to his reading and seems fine any time I check it. All looks good in that area. I know the RAP system works, retained power seems OK, I'll look for the specific odometer reading you've indicated.

Know idea about the ECM. Next time it's in the shop I'll ask the tech to more thoroughly explore the specific areas you've identified. As I've said he seems o lean to the BCM, but without any real solid reasoning, other than there have been some problems in the past due to programming (though the symptoms are far from mine) and there is no way to reprogram it, it must be replaced.

Thanks again for your thoughts and research. I appreciate your help and the other is this forum as well.

Steve
 
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