981 Heater issues.

[deMort]

Boxster , Cayman and 991 all use this system .

Car came in with blower stuck on the screen .. unable to alter the temperature or get feet / dashboard vents to work .

Fault code readout showed no communication with the 5 motors that alter temp or allow the different motors to switch venting options .

We have a LIN bus failure ..

System is a 1 zone or manual climate control .

Can bus is all the control units in the car can communicate with each other ..

Ie .. Psm/Abs tells the vehicle speed to the control units that need it .. they don't have their own speed sensors .

Lin Bus is a master and slave system .. the master being the A/C control unit with the slaves being the motors that operate the temp and position flaps .

Slaves can only talk to the master .

Both systems are binary messages the same as you would get on an office pc networked system .

Whilst we cannot see these messages ( well i can't as no equipment ) we can scope the data lines and see a signal ..

This is a square wave on a scope and will be in the region of ons and offs between 11-1 volts ..

very little access to these with the dashboard in so i scoped the only one i could on the left side with the motors connected ..

4.5 volts and a pattern that was almost a complete line .. ok that's very wrong .. possible control unit fault .

I unplugged the sensor which stopped the Lin signal going to the other motors , see the wiring diagram .. second one in ..

10.6 volts and a sensible square wave .. ok so it's this motor or one of the others that's the issue ..

I unplugged the only one i could on the right side .. same result and the other motors are now working ... it's either this motor or the last one left .. far right on wiring diagram .

This was a bitch to get at but i unplugged it and everything other than this worked .

The fault is the fresh air flap motor or solenoid if you prefer .

This is available as a separate part .. the others seem to come with a complete heater box .. bit of a result that it was this one and that i could just about get at it with the dashboard still in !!

This is more for info if you happen to get this fault or for any mechanics searching .. its not really a diy job i'm afraid .

 

[Zingari]

Great work.

I'm aware that the fan blower can cause issues on the 981 where it 'sticks' and manually spinning the blades will get it going again, until the next time. Porsche know about it but won't replace the faulty part until it goes faulty :roll:

 

[Slayer]

Great work.

I'm aware that the fan blower can cause issues on the 981 where it 'sticks' and manually spinning the blades will get it going again, until the next time. Porsche know about it but won't replace the faulty part until it goes faulty :roll:

I had mine replaced after 2 attempts at re conditioning by OPC :nooo:

 

[basilbrush]

I had a stuck fan during the winter of 2019 on my 991.2 GTS I had to pull over due to the fact that the fan would not run at all, and the windows quickly fogged up due to the cold temperatures.. i was able to lift the scuttle panel in the frunk area and remove the lid of the fan housing cover and spin the fan by hand, (it didn't feel stuck as such) however it would not spin under its own power until i did this manual intervention.. touch wood its been fine ever since..

 

[Slayer]

I had a stuck fan during the winter of 2019 on my 991.2 GTS I had to pull over due to the fact that the fan would not run at all, and the windows quickly fogged up due to the cold temperatures.. i was able to lift the scuttle panel in the frunk area and remove the lid of the fan housing cover and spin the fan by hand, (it didn't feel stuck as such) however it would not spin under its own power until i did this manual intervention.. touch wood its been fine ever since..

Best to log in with the OPC if you are under warranty to avoid time wasting if it happens again.