2006 Cayenne S - No PWM signal to the air conditioning compressor - Duratech fault code 1299 Gateway Implausible Signal

[Two914s]

I have a 2006 Cayenne S without dual A/C and I am the only person that works on it.  (I suffer from "random-mechanic-phobia")  It has ~175,000 miles on it now.

 

So,  the A/C quit working last Fall,  ...and I diagnosed the problem as a stuck solenoid valve in the A/C compressor.   This is the valve that continuously regulates whether the compressor is pumping hard, or not doing anything except turning.  (there is no mechanical clutch on a Cayenne compressor) This is a common problem, apparently, and even though I could have just purchased one of those valves,  I decided to replace the entire compressor so all the seals would be fresh.  I did test this solenoid valve outside the compressor with a battery, and it did seem to be stuck.

 

 

Well 6 months later and it is getting hot here in Atlanta, and so I have now finally evacuated the system with a vacuum pump down to 400 micron (Hg) and am trying to fill the system with R134a.   I think I am well above the pressure needed to satisfy the low refrigerant pressure switch.....  But,  I now notice that I am not getting any PWM (pulse width modulated) signal from the "climatronic" control unit to the compressor.  (I have measured this with an oscilloscope.)   I do have +12 volts at the compressor from Fuse 11 in the engine fuse box on the red/blue wire, but I don't have the modulated ground signal that comes from the control unit (pin E4) on the violet/white wire.

 

So, I did some Duratech diagnostic scans and, after clearing faults, and re-scanning the AC system,  I get a persistent  "1299 Gateway Implausible signal" fault.

 

When I scan the Gateway, I don't get any faults except "459 PCM2" which I assume is because I have an aftermarket sound system installed.  (PCM = Porsche Communication Management)

 

What does this "1299 Gateway Implausible signal" fault point to?   What does it mean?   Is the "Gateway" the same as the CAN bus?  How does one normally interpret these fault codes from Duratech?

 

And,  how do I jumper the refrigerant low / high pressure sensor to make sure it isn't holding up the operation?   It is a three wire sensor, not a two wire sensor.   Pin 1 (brown wire) is connected to ground,  Pin 2 (yellow/blue wire) goes to the "climatronic" control unit (Pin C23),  and Pin 3 (Red/Green wire) is +12 volts from Fuse 10.   Does the yellow/blue wire have a connection to ground or +12 Volts when the system is in normal pressure ranges?

 

 

Thanks for any help on this!!

[JFP in PA]

The gateway is the CAN Bus system module, and it is seeing a signal that it does not recognize or understand.  You may need access to a PIWIS system to diagnose the gateway module issue further.

[Two914s]

OK,  after some more research I can answer more of my own questions.

 

I called an accomplished independent Porsche repair shop in my area and they said that they couldnt adequately diagnose problems with the gateway/CAN bus in my Cayenne S, nor did they know of anyone in the area (Atlanta, Georgia) who could.   They very sadly said that I must go to the dealership.  They said that the PIWIS systems weren't going to help me much.  But, I am not quite convinced.

 

And, I discovered that the 955 Cayenne AC system doesn't have a low / high refrigerant pressure switch like older cars, it has a SENSOR.  This sensor has three wires (as seen above).  The wire that returns to the "climatronic" control unit delivers a PWM signal that tells the control computer what the pressure is in the line.   The computer logic then decides if the pressure is too high or low.  So, it isn't a switch that can be bypassed with a jumper wire.  Here is a description from a Porsche manual...

 

 

[Nick Wallis]

Hi I have the same problem, did you ever manage to fix it? If so how?

[Two914s]

Hello Nick and everyone else,

 

After much frustration,  I took the car to the dealership and asked them to fix my problem.   I was thinking that something was wrong with the climate control unit.

 

Well,  the dealership got it working, but then I was embarrassed.   Instead of buying a compressor that was specifically for a Porsche Cayenne,  I bought one that had a slightly different electrical connector on it because it cost much less.   I bought part number  GPD 9641834    from Rock Auto for under $300.

 

Well, when I connected the wires with my own connector, I got them reversed, so that is why the compressor wouldn't come on.  Apparently when the wires were swapped back the compressor started working and the system was able to be charged.  I have had working A/C since.

 

I have checked the CAN bus and I still have the same "1299 Gateway Implausible signal" fault,  so that must not have actually had much to do with my A/C problems.  I still have no idea what is causing that code, or what it really means.

 

Sorry I couldn't help more.

 

 

[Nick Wallis]

17 hours ago, Two914s said:

Hello Nick and everyone else,

 

After much frustration,  I took the car to the dealership and asked them to fix my problem.   I was thinking that something was wrong with the climate control unit.

 

Well,  the dealership got it working, but then I was embarrassed.   Instead of buying a compressor that was specifically for a Porsche Cayenne,  I bought one that had a slightly different electrical connector on it because it cost much less.   I bought part number  GPD 9641834    from Rock Auto for under $300.

 

Well, when I connected the wires with my own connector, I got them reversed, so that is why the compressor wouldn't come on.  Apparently when the wires were swapped back the compressor started working and the system was able to be charged.  I have had working A/C since.

 

I have checked the CAN bus and I still have the same "1299 Gateway Implausible signal" fault,  so that must not have actually had much to do with my A/C problems.  I still have no idea what is causing that code, or what it really means.

 

Sorry I couldn't help more.

 

 

Thank you for the reply..... i am pretty sure the gateway fauly implausible signal is a red herring as I found it on cars with working ac....I like you have tried to save money and bought a recon denso....i wonder if my wires are crossed! Thx again