brock911

Identified a "0234" fault code today... "Turbo - Super Charger Overboost condition".

Did a search on this forum and came up empty on results.

The car runs good without hesitation upon acceleration and no odd behaviour.

I did have a CEL diagnosed by the dealer as 0491 and 0492 relating to SAI system but I'm not sure if the two are related, any ideas what I might be up against?

Online search reveals the following...

OBD Code P0234refers to
The PCM disables (bypasses) the supercharger boost and sets a diagnostic trouble code (DTC) to keep from damaging the powertrain (engine or transmission) during potential harmful operating conditions.

Symptoms
Possible sumptoms of OBD code P0234
- Engine Light ON (or Service Engine Soon Warning Light)

Causes
Possible causes of OBD code P0234
- Brake torque (brake on and throttle at wide open). - Transmission oil temperature (TOT) exceeds calibrated threshold. - Engine over temperature. - Ignition misfire exceeds the calibrated threshold. - Knock sensor (KS) failure

Possible Solutions
Check for other diagnostic trouble codes accompanying P0234, or check appropriate and available PIDs related to the above possible causes.

dubyaTT

Is that the only code stored or pending?

brock911

The 3 codes were, 0491,0492 & 0234 stored now cleared.

jpflip

You got a vacuum line going to one the waste gate or going to the n75 valve leaking. 0491 is also related to one of the vacuum line leaking.

brock911

Thanks J.P., is it possible that the 0491 & 0492 are related to the 0234 being a vacuum leak and is this also related to SAI?

When the dealer diagnosed the 0491 & 0492 codes a few months ago there was no mention of the 0234, this must have developed recently but didn't throw a "new" CEL because I was already getting one.

First, how will I be able to tell if its one of the waste gate lines or the n75 valve (not sure what this is) and can you share with me what is involved in repairing this, is it easy enough for me to do or a dealer repair?

Thanks again for your help,
Mike

jpflip

Mike, all three fault codes can be related. The problem is you got a lot of sense lines on the TT and it goes from the secondary air pump to the diverter valves and switch over valve etc.... One of these line must be leaking. I would start with a good visual inspection of all the small black plastic line and their rubber attachment (after airbox removal or better, intake removal). Also, if you are equip to do it, a boost leak check can also help a lot since you are pressurizing the intake and at the same time the sense lines connected to the intake manifold.

brock911

Thanks again JP, I was reading about the gauges being made to pressurize the system post MAF to identify leaks in the system, unfortunately I'm not equipped to do this.

If there is anybody in the Niagara area of Ontario that has done it or can provide some assistance please let me know?

Thanks again for the help,
Mike

Kevin

Mike, what did the dealer fix when you had the previous codes? Did they replace anything??

Here is the factory DME troubleshooting for your CEL.. I recommend that you check your wastegates on your turbochargers to make sure that they are moving, check your actuators so that they can "move" the gates. I am seeing seized wastegates due to corrosion. It's a turbocharger replacement if that is the case. The last thing to check after you have verified your wastegate movement is your N75 frequency valve which supplies pressure to your wastegate actuators..

P0234
Boost Pressure Characteristic, Upper Value Exceeded
- Above Limit
Diagnosis conditions
• Charge pressure control active
Possible fault cause
♦ Leakage at pressure hoses from frequency valve to the bypass
flaps
♦ Frequency valve faulty
♦ Vacuum modulators for bypass flaps leaking
♦ Bypass flaps incorrectly adjusted
Affected terminals
Diagnosis/Troubleshooting

brock911

Hi Kevin, thanks for your input on this. I checked out your website and appreciate your advice.

When I had the dealer diagnose the CEL as a SAI system issue and being told this is not a performance affecting matter and only an issue at time of emission testing, (which the car passed only a month or so before) I didn't authorize any repairs because they couldn't say for certain what the actual problem was. I get sensitive when I'm expected to pay for the service technician to go to "school" on my cars.

I'm not the DIY kind of guy so would like to learn more about the issue, I now understand that it may not be the SAI pump itself and could be related to a leak somewhere etc. The engine had been removed in the past by the dealer for other repair work (prior to my ownership) so it may be related to an improper re-install, poor connection perhaps but can't be certain of this?

I believe this "new" fault code is related to a recent test drive (car is for sale), when the prospective purchaser got on it a few times, the car performed fine, at least I didn't notice a problem as the passenger but then this code was diagnosed following the test drive. He brought along his own $29.00 diagnostic tool and checked it, this is when 0234 showed up.

What is involved with checking the wastegates on the turbochargers and approx cost to identify and repair?

If it is the turbocharger/s would the car still perform well?

Also, if it is the N75 frequency valve can you give me an idea of cost to replace?

Very much appreciate your opinion.

Regards,
Mike

Kevin

The tests on the wastegate and actuator needs is not intended for a non DIYer.. You will have to get your hands dirty for these checks and the car up in the air or on blocks..

The info that I posted is right from the Porsche DME diagnostics.. If I was to bet on the issue I would be looking at sticking wastegates, next is the N75... Basically your engine is not controlling boost, and you are getting boost spikes...

You will have to spend some money at the dealer for the diagnostics and the physical checks that need to be examined. You can print out my post and hand it to the Service advisor..

jpflip

Mike I encourage you to take a look at your engine. Just remove the air filter box and you will get a better view to some of the sense line and the N75 valve which is attach at the right side of the intake assembly. Some of those sense lines get detach easily and you just have to reposition them into their connector. Replacing the N75 (part#996 605 155 00) valve is also easy and really cheap, only about $25.00....

993GT

Hey Mike, why not swing by Auguste's and have him figure it out?
Cheers,

brock911

Hi Rob, hope all is well... Congratulations on the new acquisition. I was speaking with Darrin and he shared the news, pretty amazing ride isn't it?

Give my regards to your dad,
Mike

adam_

Others will correct me, but this code is more likely to be set when the car is operated at or new full boost mode. At the boost builds and the DME sends commands to N75 to control (ie 'dump') excess boost...but it cannot due to the leak..the boost then builds and goes over limit, tripping the code.

The test drive didnt 'break' anything, just uncovered it. IMO

You want someone to just go through the vacuum lines between the wastegates, N75 and manifold, and test the N75. Couple of hours? The problem of course is finding someone knowledgeable that wont take advantage of your lack of DIY skills/knowledge- perhaps pad the effort or worse (if they arent that knowledgeable) chase issues that arent...


GL

A

993GT

Hey Mike,
Thanks! It's good to hear from you, it's been a while!
Still have to show Darin the new car, it's an absolute machine!
Are you still running Autosport?
My Dad and I (and maybe Darin?) will have to meet up with you one of the times I'm down in your area with the GT2.
Cheers,