Help with intake leak code

[Jons1001]

Hi all, the following code keeps coming back on my mk5 gti.

P2279 - Intake air system leak

Car seems to be driving fine, boosts normal and mpg is ok.

I did the dipstick test and it definitely doesn’t sound right

Does this point to Pcv valve?

Pcv was changed approx 30k miles ago and diverter valve 40k miles ago.

Any further tests I can do to single out the issue or should I take it to the garage for a smoke test?

Thanks

[GVK]

Smoke test if you can get it done locally

[Jons1001]

Update:

Took it to the garage for a smoke test and they found that a screw was missing from the MAF sensor (should really have spotted this myself!) and a blanking cap was missing from the vacuum line. This was sorted and a second smoke test showed no leaks however 2 days later the code is back along with others.






Does anyone have any ideas of what I could do next to check what is causing this? I’m going to take it back to the garage to get their opinion but don’t want to start throwing money replacing DV, PCV, MAF sensor etc if there is a way of narrowing it down.

I have obdeleven if that helps with any diagnosis.

Cheers

[mjmallia]

Sounds like PCV to me as pulling the dip stick out would make the car almost stall and hate that it was even turned on.

Was it an original PCV as I once used an aftermarket one that failed within a year, put an original on and its been fine for much much longer since.

[Jons1001]

Sounds like PCV to me as pulling the dip stick out would make the car almost stall and hate that it was even turned on.

Was it an original PCV as I once used an aftermarket one that failed within a year, put an original on and its been fine for much much longer since.

Hi yes it was a genuine PCV. I'm edging towards maybe changing the PCV & possibly DV aswell and see if that solves it.

[mjmallia]

The corrugated plastic hoses also crack and become brittle (age and heat cycles).  I replaced both of mine due to cracks that I could not see......the two from the PCV.

[Jons1001]

The corrugated plastic hoses also crack and become brittle (age and heat cycles).  I replaced both of mine due to cracks that I could not see......the two from the PCV.

Thanks for the info will check. Is it possible that a failing PCV wouldn't show anything on a smoke test though? as they reckoned everything was good with no apparent leaks.

[mjmallia]

You can take it off and blow into it.  Air should be flowing one way and not the other, via the valve.

[ZoliWorks]

Pcv sounds fine to me. Pulling the plug, the engine clearly start going rough but it stabilizes itself and increases the rpm. Thats normal. If the pcv was bad, you'd get misfires, running lean codes and the engine would tend to shake at idle, especially after starting.

On the other hand, if there's a vacuum leak, what will happen is the engine will stabilize itself after 2 minutes or so and then if you pull the dipstick or take the oil cap off, it will make no difference. This means there's a constant air leak in the system.

But yeah, if it hasn't been done, it's worth replacing. Another thing that went bad for me was the brake booster vacuum hose. The plastic hose that goes from the check valve to the vacuum pump cracked and created a constant leak.

[Jons1001]

Pcv sounds fine to me. Pulling the plug, the engine clearly start going rough but it stabilizes itself and increases the rpm. Thats normal. If the pcv was bad, you'd get misfires, running lean codes and the engine would tend to shake at idle, especially after starting.

On the other hand, if there's a vacuum leak, what will happen is the engine will stabilize itself after 2 minutes or so and then if you pull the dipstick or take the oil cap off, it will make no difference. This means there's a constant air leak in the system.

But yeah, if it hasn't been done, it's worth replacing. Another thing that went bad for me was the brake booster vacuum hose. The plastic hose that goes from the check valve to the vacuum pump cracked and created a constant leak.

Hi thanks for the reply. Just got back from the garage and they are saying the second code is pointing towards the lambda sensor (post cat). I think the plan is to replace the PCV, and then do a continuity test on the lambda with a view to possibly replacing that if it is showing as bad. Thing is i had the same lambda issue 2 years ago when i went back to the mapping company to get the map tweaked after fitting a sports cat.  They said the lambda was damaged and they replaced it. A week or so later the code was back. However this code only seemed to appear every 500-1000 miles after clearing, which i put down to the map. The code relating to the vacuum leak won't go away. 

They are telling me after the second smoke test there were no leaks showing, so either it is the lambda sensor causing it, or something that wouldn't show in the smoke test (PCV, Diverter valve?) or they have missed something e.g very small leak from a hose - possibly obscured if it was resting on another hose etc.

Very frustrating!

[ZoliWorks]

Well if you have a sports cat, the post cat lambda reading is way out of factory spec because a sports cat flows better than the 2 stock cats. It filters out less so the lambda read different values. You either need to get the 2nd sensor mapped out / adjusted via the map or you use a spacer to space out the sensor from the downpipe, making it read closer to factory specs. It will start popping up more and more frequently cause sports cats are cheap and way lower quality than factory cats so they burn out sooner and their efficiency decreases. Some guys here replace them once every 2-3 years cause they no longer pass inspection. I've only had mine for half a year and the tone of the engine changed drastically since I first fitted it. I'll likely have to replace it next year if I want to pass checks.

[ZoliWorks]

Also, about P2279



https://www.obd-codes.com/p2279

[Jons1001]

Well if you have a sports cat, the post cat lambda reading is way out of factory spec because a sports cat flows better than the 2 stock cats. It filters out less so the lambda read different values. You either need to get the 2nd sensor mapped out / adjusted via the map or you use a spacer to space out the sensor from the downpipe, making it read closer to factory specs. It will start popping up more and more frequently cause sports cats are cheap and way lower quality than factory cats so they burn out sooner and their efficiency decreases. Some guys here replace them once every 2-3 years cause they no longer pass inspection. I've only had mine for half a year and the tone of the engine changed drastically since I first fitted it. I'll likely have to replace it next year if I want to pass checks.

Thanks, the sports cat already won't pass an mot as of last year...

It's good that you mentioned the two different readings as the mechanic was saying he read mine and they were different which points to a bad sensor, however i now know that it is just the map. I asked them (remap company) about this when i got the map tweaked - guess they just sold me a Lambda sensor when i may not have needed one. Surely an established mapping company like they are would know to map out the lambda sensor though 

Still a bit stumped then, probably going to fit a new PCV and go from there.

[ZoliWorks]

I'm not sure exactly if the 2nd sensor is just a check sensor or if it actually influences the fuel trims in anyway. On the forums I've heard it's only there to test the cat efficiency and doesnt actually influence fuel trims but one of my mechanic buddies claims it does influence trims.

If it does influence trims, then it needs to be mapped out or spaced out to get rid of the error/CEL. I'm not actually sure if mine is mapped out or I just got lucky and it hasn't thrown a cel but I'm leaning towards the fact that it's mapped out since I did specify to my mapper that I have a sports cat.