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Help…I may have done something stupid! loss of PCM functions.(long

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When I got my car, 2005 997.1 Carrera 2S RHD (UK) it had the 2004 Nav disc. I obtained the required discs and updated it with and 000.044.901.40 then inserted the 2008 disc 000.044.901.40 and then the 2012 disc 997.044.903.50 and it all worked OK. I didn't use the as I could not determine if I had the Motorola phone module or not. Went away on holiday and the stereo, trip etc all fine but the Nav said that the disc was unreadable. Got home and tried to load the disc as I thought it might have been that, it said loading phone etc but halted on the progress bar and stopped there. I removed the CD from the Nav unit and re-booted and now I have 'System Error, Amplifier, CD Player, Nav System, Phone not available' I disconnected the battery for 30 minutes, reconnected and removed and checked fuses C F2,F8,F9,F10 D F9,F10 all OK. Reset everything with Durametric and it tells me that errors C203 PASM 'fault steering wheel electronics control unit (drive) and Air Conditioning C141 ' communications PCM display' and C131 'communication gateway control unit CAN comfort no signal communications' they will not clear.

Pressing MAIN and TRIP simultaneously gives me Soft Ware versions 3.0 then two triangles below with 'unknown' next to them.

When I check on the software status of all units I get:-

Unit :- Amplifier

Target:- 000 17500/3504

Actual:- ---/----

Entered:- Yes

Found:- No

Unit:- CD Changer

Target:- C38/3003

Actual:- ---/---

Entered:- Yes

Found:- No

Unit:- Navigation System

Target:- ---/---

Actual:- ---/---

Entered:- Yes

Found:- No

Unit:- Phone

Target:- 05034 B54/0305

Actual:- ---/---

Entered:- Yes

Found:- No

Unit:- PCM

Target:- 05024 AD1/0205

Actual:- 05024 AD1/0205

Entered:- Yes

Found:- Yes

Unit:- System Software

Target:- 04364AD1/3604

Actual:- BOL03AD1/4303

Entered:- Yes

Found:- Yes

Sport now fails to come on and I get PASM failure and PSM failure.

1,4,8 reboot no change to anything, Nav DVD and amplifier have the optical signal to them as I can see the red light!

Abject apologies for this being so long but HELP!

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Hi jl,

My guess is your PCM control unit is bad. This is a tough situation. The various control modules in the car are in an electronic chain of command at the hub of which is what Porsche calls a gateway module. The PWIS diagnostic testor will report a failure of this module if just about anything downstream goes wrong. When my PCM unit failed the car reported a PASM failure and the PWIS first said my gateway module failed. After replacing that it reported a failure of my instrument cluster. $9000 later the tech disconnected the PCM unit and everything went back to working just fine. The PASM did have to be reprogrammed. It can be very difficult to determine which device has failed and if you get your Porsche specialist going he will start replacing one after another at huge expense. Fortunately, I had my car certified so this was all covered under warranty.

I would start by disconnecting the PCM control unit. You might try pulling fuse F8 in Row C which should disable the PCM and see what happens. If your PASM starts fuctioning again you know for sure it is the PCM unit. If not then you will have to involve somebody with a PWIS tester. If the PASM can be reprogrammed and made to fuction then you are back to a bad PCM. You need to figure out what you are going to do about the PCM unit. My advise is to junk it. Get a NAV TV MOST head unit replacement module, a double DIN replacement kit with factory finish and a new NAV from either Kenwood or Alpine. I like the Alpine INE 927 HD. You will get better sound, a MUCH better NAV with Bluetooth and great iPod integration thrown in. Getting the Alpine will not cost you much more if not even less then replacing the PCM. My car has the Bose upgrade in it and with the Alpine's digital equalization and time correction sounds way better than stock. Good luck!post-89070-0-80969900-1370223142_thumb.j

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The PCM message is typical of what happens when there is a break in the MOST loop. The 'System Error, Amplifier, CD Player, Nav System, Phone not available' messages are all from devices connected by this fibre-optic loop. Hence you can see the software versions of the devices in the head unit, but none of the external devices.

Just a thought. Can you eject the CD changer cartridge? I saw one last week where the internal fuse in the CDC had blown, and it had all the PCM error messages the same as yours.

Also, there is a possibility that the failed phone update has caused the PCM unit to lose its coding. I have seen this happen before too.

I don't think either of these would explain the PSM/PASM error messages though. As has been suggested, a diagnostic check is the starting point for troubleshooting problems like this.

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Thank you both for the replies. I thought for a while I was alone with this, it seems not!

As you both say, it appears to be a software issue in one form or another. Will do more investigation and see if I can make sense of it. Will report back success or failure or in-fact if I decide to junk it in favour of replacement route.


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  • 1 year later...

Here is the short version.  I had the same message come up. ( System error: Amplifier, CD Changer, Navigation System not available.) It turned out to be a bad amp.  I replaced it ($1400.00) and everything works like new.

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  • 2 years later...

A good way to troubleshoot is to get a MOST loop connector so you can bridge out each component in the MOST chain one by one until the error goes away. I found similar errors when I removed my factory CDR24 headunit and fitted a Pioneer AVIC-7200NEX headunit. Got loads of fault codes until I coded the radio out of the system with Durametric and fitted a MOST loop connector onto the loose MOST plug.


most connector.JPG

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