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997-1: CEL Cooling system performance

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Hi everyone,


I’m new as a member to this forum, although I’ve been silently reading for years. I own a 99 Boxster and a 2005 997 Carrera S, both in midnight blue on tan. I used to also own a 2005 Boxster S, also midnight blue on tan, until I got rear ended on the highway.


My 2005 997 Carrera S is acting up and throwing error codes. I spent quite a while reading about what this might be and I’m running out of ideas, so I’m calling out to the community to see if anyone has any better idea worth exploring.


The facts:

- Check engine light with code P2081 (cooling system performance) and sometimes also P3081

- Most of the time, I get a CEL, and sometimes also the blinking red light by the coolant gauge, with the coolant gauge dropping to 0.

- Resetting the code helps for a few miles, then the codes come back.


When does this happen?

- I have noticed that this happens when the weather is colder. I live in San Francisco where the weather is a bit colder (55 degrees). I spent a week in LA where the weather was in the high 80s and did not get the codes until I got back to San Francisco.

- This started happening right after I did an oil  + air filter + cabin filter change + added some official Porsche coolant. Not sure what might have gone wrong in this process or if this is just a coincidence.


What have I tried?

- My mechanic has tried replacing the thermostat and the temperature switch, without much effect.

- I noticed that one of the vacuum lines going the the air box was unplugged. I just re-plugged it but it didn’t make any difference. I read somewhere that there was an issue with these codes and vacuum leaks on GT2 or GT3 but I’m unsure how to diagnose this further or what else to do besides re-plug that line.


Other symptoms

- Possibly related: it happened only twice, but I was on the highway and lost power for about 10s, then regained power and this issue never happened again for a while.

- Possibly unrelated: I recently got new issues related to the PSM (PASM failure and PSM failure). The codes are 000D, 000E and 000F (FR/RL/RR shock absorber valve)


Any suggestions is welcome. Thanks much!

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Are there indications of it overheating? If yes, have you tried ' burping' the system and was the Porsche coolant that you used to top-up the same as was already in there? You presumably did dilute it with 50% distilled water?


How many miles on the car, have you replaced the water pump and, if yes, was it with a Porsche original pump?


You may also wish to check your mechanic's work on the temperature switch.

Edited by wizard
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Hi wizard,


Thanks for your comments. I don’t see any indication that the car is overheating. Most of the time, the coolant temperature is right in the middle. It does take a while for the car to warm up though.


I did not try to burp the system but I’m guessing my mechanic did when he replaced the thermostat. I’ll check. The coolant was 50/50 diluted with distilled water and was the same original Porsche coolant as was in the car.


The car has 80k miles and the water pump has not been replaced as far as I know.

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1 hour ago, JFP in PA said:


Not sure, he could have replace the thermostat, which is different.


He replaced the thermostat first, then the problem came back and he replaced the temperature switch then, but the problem still came back.

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33 minutes ago, Enaifos said:


He replaced the thermostat first, then the problem came back and he replaced the temperature switch then, but the problem still came back.


OK, my next move  would be to have the car scanned with a Porsche specific scan tool and look at the actual coolant temperature values to make sure they are were they should be.  If everything is good, I would read and note all codes, then clear them and see if they return.


We have seen fault codes are P2181 (thermostat stuck open) and P3081 (engine coolant temperature implausible) on GT cars caused  is a blocked valve on the trans cooler (photo), but your car should not have that.



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