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On my recent drive from Ohio to Florida, I encountered rain ( a monsoon) for about 7 hours. In the aftermath, the car developed a fault in an electronic change-over valve (or as I call them, vacuum solenoid actuators). There are several in the car (doing various functions controlled by vacuum) and on PDK cars, there are two that control the flow of coolant to the PDK water to oil heat exchangers, one for ATF and the other for the gear oil (there is one for the single heat exchanger on a manual transmission). Apparently the bad valve (or valves) filled with water.

In research, there have been many variations of this device over the years. By their design, when the actuator closes, it must open the controlled device to atmospheric to relieve the vacuum so the device will return to the normal position. In any case, over the years, Porsche has tried several designs, mostly with protecting the atmospheric port from water, as once water enters the atmospheric port, the change over valve is toast. Other places that this actuator is used is on the intake plenum flap for S and GTS models, and to reroute warm or cold air to the air filters. Apparently the computers can detect when the valve fails as it logs as an error via CANBUS, which is what happened to my car.

The replacement actuators are cheap, under $40 each, but the PDK ones are under the Y hose that connects to the throttle body, so you have to remove the engine lid to fix. I didn't have inclination to do so on the trip, but would have done so if an over temperature warning occurred (I was having the 3rd radiator kit installed at the time).

From what I have read, the first 991s were recalled under campaign W43 to have up to 8 valves per car replaced, but the 981 actuator design has protected the atmospheric port better than the original 991 design. In my case, the valves appear to be stuck to let coolant flow full time, which increases the warm up time. I did not receive an instrument cluster warning, only a scan by a PIWIZ detected this.

Anyone else have to replace one? Just reinforces my desire to only run the car when it is nice out!
 
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