alland

I'm still trying to resolve intemitent PCM failure. It seems to come in bouts and happens on smooth pavement or rough. The loss of audio (nav,cd, etc) is preceded by a brief, abrupt, loud zapping sound that is best compared to a sci-fi sound effect for a laser impact. It is not the ppping sound that I associate with an electrical short but, as I've never heard what a problem with fibre optic connections sounds like.... I'm guessing this is what it is. How would one diagnose/confirm this and what are the repair options? I'm about to install the itronic BT module so will be taking out te head unit this weekend. is there anything that I should check while I'm there?

The PCM display gives a message along the line of "CD, Nav, phone... not available" when this happens.

mudman2

Without a PIWIS to read any error messages and based on history I would say your Bose amp is biting the dust. This would be especially the case if the MY is 04/05/06

alland

I plugged the Durametric in and it gave the diagnostic code 778 "steering-angle sensor". Under the diagnostic menu it offered "calibrate steering angle" . Running the calibration option (not sure what this does) did not make any difference. The PCM still shows the error message "Navigation, CD, Amplifier.... not avaiable".

I'm taking it into the dealer on Thursday to have them take a look at it. With the fact that the problem became terminal after I installed the Mobridge BT module I'm anticipating that they will blame my installation. I'm also concerned that this may void my aftermarket waranty and so am considering taking the module out before I go in. Any thoughts?? Don't really want to spend the evening in sub zero temperature with a flashlight undoing something that is unlikely to be the cause. But if it is likely to void my warranty .... I'll do it!

Iloveheat

Hey, I don't know what vehicle you have, however: I have a 2004 Cayenne, and pretty much I have the same problem, the error message that says "...amplifier no available". the navigation works, but no audio at all. I disconnected the CD changer, and nothing changed, but the message that only says that the amp doesn't work. Now, it started with intermitten frequency, a day it was working, the other it wasn't. I turned off the engine and restarted it and it was working. Loud noise and stopped working, not working at all. Now it hasn't worked for a month, and yesterday once gotten to destination, I stopped the engine, removed the key, and thought to start the radio and ...bang, it worked! I repeted the experiment today after the 16 miles trip to the office and it worked again. So what the F... is going on? it's not the amp, it's not the optical cable in my opinion, it's not the fuse....what the heck is it?

alland

Ooops maybe this will be more helpful to anyone who's been reading my monologue. First time using the Durametric and I took the codes from the PSM when I needed to go under "Gateway" to get codes for the PSM. The correct error codes are 459 - PCM no signal, and 532 Power supply-short to ground/pos. I wonder if this means that the power connections on the Motronic are shorting?


Anyone know where you can get more info on these codes or further troubleshoot the problem without relying on the dealer?

Iloveheat

it's strange, but that what I thought too. I thought it could be a ground problem. Not at the battery though, I had the battery replaced a week ago, and thus (I want to hope) the job was done correctly and all nuts and bolts were tightened. so.... i checked the ground bolt in the rear of the vehicle, left and right in the trunk inside where you have those emplty spaces. they seem ok to me, so.... WHY WHY WHY all of the sudden? what is the cause? what is it?

mudman2

On the 04's there were software and firmware updates for the Bose amp which were supposed to correct that but a lot of time the amp had to be replaced

Iloveheat

Do you know where I can find this update? or is it somehting that eventually was done by the dealer?

mudman2

Its installed using PIWIS and in accordance with a TSB I seem to recall, sign up on Renntech and get access to the TSB's

alland

thanks Mudman

ltc

He did it on purpose ...

mudman2

OK No Fair ! a newby will NEVER get that one.

ALLAND, there is a rumour that a person of certain engineering acumen was involved in the design of the BOSE amp. Sadly that person died some years ago but still haunts our Obergrupenfuhrer down in his bunker.

It is also rumoured that the amp has some built in suprises to pay PAG back for being cheap. Of course PAG drive VW's so they never see the problem.

Iloveheat

Last update: it's sure and official now, the amp doesn't want to work unless the outdoor temperature is about 72 deg, and it doesn't rain. this is the true, I am not BSing. I refuse to replace the amp, when the amp itself does work, when it wants to work. What is it?

ltc

Early FOT (fiber optic transceivers) were incapable of running at rated temperature, so when the temperature began to rise close to 80degC, then a software controlled shutdown was initiated (with full shutdown at 85degC)

Also, the early FOTs were known to have a 'fogging' issue; this was due to outgassing, which was accelerated with temperature. There were both Tyco and Yazaki MOST FOTs....IIRC, Porsche required that only Yazaki FOTs be used in their vehicles across all MOST devices.

So, your 2 most (no pun intended) likely places to start:
1. the fan in the amplifier is failing or has failed.
2. the FOT has fogged/degraded.

The fan is easy to fix/verify...try driving with the passenger side rear cargo cover removed to verify fan operation at high volume/power dissipation/temperature.

The FOT is actually easy to fix as well, It is a thru hole device which can easily be removed from the PCB and a new one installed.

Iloveheat

WOW! thank you so much! One more quick question: where can I find the FOT? and furthermore, I used to "play" with amps and speakers when young, and i used to disassamble several trunks in several vehicles, but the cayenne's...one bitch! don't know where to start, it's either my age, or they really changed the way they build this side compartment covers...damn it. I think I am going for the FOT since the amp doesn't work if the temp is cool, and not vice versa, which is very common indeed (over heating protection). thank you again!