P0234 after going Stage 1

[keithk831]

Hi folks,

I just bought my 2014 A4 2.0T about a month ago. About two weeks ago I went with a Unitronic Stage 1 (91 octane) tune. Everything has been fine up until now, however today while driving with the family my EPC light came on and my car had very little power, especially above 2000rpm. I figured it was in limp mode so I drove home and hooked up my OBDII scanner. The only code was P0234, which appears to be an overboost code.

I also noticed that my engine bay was REALLY hot. Like, I half expected my exhaust manifold to be glowing.

Anyway, I cleared the code, checked for boost leaks and went for a drive. The car's power seems to be "normal". I'm a bit nervous about this. Any suggestions?

[van462]

Look at the wastegate actuator on the turbo. The factory one will be a matte silver. If the one on there has been swapped out to an after market one like forge or chinabay then the spring rate of the wastegate may not match what the ECU expects. Also check the hose going from the actuator to the n75 valve is not cut or cracked. Overboost is a very uncommon fail on this car. The wastegate not opening to allow the turbo to slow down is usually the culprit or a DV not opening to bleed off boost when you let off the gas.

[The Infiltrator]

http://www.audizine.com/forum/showth...ault-Code-List

[keithk831]

http://www.audizine.com/forum/showth...ault-Code-List

So this is what's listed in the link you provided: 16618 P0234 wastegate: the output of the control range (greater than the upper limit)

So it sounds like the wastegate is the issue?

[keithk831]

Look at the wastegate actuator on the turbo. The factory one will be a matte silver. If the one on there has been swapped out to an after market one like forge or chinabay then the spring rate of the wastegate may not match what the ECU expects. Also check the hose going from the actuator to the n75 valve is not cut or cracked. Overboost is a very uncommon fail on this car. The wastegate not opening to allow the turbo to slow down is usually the culprit or a DV not opening to bleed off boost when you let off the gas.

I'll go check in a bit, but i'd be shocked if there's an aftermarket part on this car. It was completely stock (to my knowledge) and there didn't appear to be any evidence of current or former mods.

By the way, the EPC light came on again on the way home today. Same code.

[keithk831]

Looked under the hood again. I didn't see any issues with the wastegate actuator (from what I could see), or any disconnected or damaged hoses around the turbo...

[Alex1188]

Check the n75 valve, it could be stuck in a shut position. To check just disconnect the electrical connector on it and it should default to the open position allowing you to run off Watergate pressure only, meaning you should only be able to make like 6psi of boost. If you still make a shit ton of boost with it disconnected the n75 is bad.

[keithk831]

Check the n75 valve, it could be stuck in a shut position. To check just disconnect the electrical connector on it and it should default to the open position allowing you to run off Watergate pressure only, meaning you should only be able to make like 6psi of boost. If you still make a shit ton of boost with it disconnected the n75 is bad.

Thanks, i'll give that a shot.

I contacted Unitronic today and they said that it's a well-documented issue on these engines to have the wastegate actuator go out of alignment, resulting in an over/underboost condition. They suggested I may need to have the wastegate/turbo rebuilt...

[keithk831]

Update: I bought a new N75 sensor and plan to replace it Saturday morning. We'll see what happens. Last weekend I removed my Stage 1 tune (back to stock) and for several days didn't have any CEL issues. On Tuesday I put the tune back on the car and today driving home the EPC light came on. I was accelerating at about 1/2 throttle when it came on. P0234 again.

I also noticed that the car has some hesitation when boosting/under load. It's there regardless of whether the stock tune or the stage 1 tune is on, but it's more pronounced with the stage 1 tune.

Any other thoughts? Does this reinforce any previously suggested ideas?

[keithk831]

Another update: This morning I replaced the N75 sensor, then went for a drive. No EPC light (though it hasn't always come on). Still a little bit of hesitation, though that could be attributed to the ECU re-learning. Also, there was a tiny bit of oil in the old N75.

One significant observation though: Before replacing the sensor, I never heard the diverter valve do it's thing before. At the end of my test drive, I heard it for the first time. I'm also hearing more of the turbo "whoosh" than I did before. Perhaps something was wrong with the N75?

[Alex1188]

Another update: This morning I replaced the N75 sensor, then went for a drive. No EPC light (though it hasn't always come on). Still a little bit of hesitation, though that could be attributed to the ECU re-learning. Also, there was a tiny bit of oil in the old N75.

One significant observation though: Before replacing the sensor, I never heard the diverter valve do it's thing before. At the end of my test drive, I heard it for the first time. I'm also hearing more of the turbo "whoosh" than I did before. Perhaps something was wrong with the N75?

Hard to say unless you get another code or do some Data logging. But if the car feels better that was my guess from the beginning was the n75. Oil could have possibly killed it but hard to say.

[keithk831]

Well, the bad news is I don't think my problem is fixed. I've replaced by N75 sensor and diverter valve.

I've noticed that my car has some hesitation around 50-75% throttle in the mid-rpm range. I assume this may be related.

Other ideas?

[nycaudi]

Throttle body adaptation . Liquid moly fuel injector cleaner in a quarter tank, then drive it like a racecar

[sparkster]

Well, the bad news is I don't think my problem is fixed. I've replaced by N75 sensor and diverter valve.

I've noticed that my car has some hesitation around 50-75% throttle in the mid-rpm range. I assume this may be related.

Other ideas?

You find the cause and solution?

[keithk831]

Not yet. I replaced the spark plugs and the car drives a little better, but the hesitation is still there. No CEL though.


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[sparkster]

thanks for update. Just got the P0234 code, haven't troubleshooted yet, but going into limp mode when I push it recently.

[kdaffy]

i would also check for leaks, make sure your PCV is in good shape and see if there is any play on your wastegate as well. also check the feeds into the N75...if any of them are cracked/faulty, could get this fault.

On the Ross-Tech site there is some more info:

16618/P0234/000564 - Boost Pressure Regulation: Limit Exceeded (Overboost Condition)
Possible Symptoms
Malfunction Indicator Light (MIL) ON
Boost Pressure too high
Reduced Power Output
Possible Causes
Hoses incorrectly connected, disconnected, blocked or leaking
Boost Pressure Control Valve (N75) faulty
Boost Pressure Sensor (G31) faulty
Turbo Charger stuck/faulty
Possible Solutions
Check Charge Pressure Control System
Perform Output Test (to check the Turbo Charger)
Perform Basic Setting (to check the Charge Pressure Control)
Perform Pressure Test to locate Leaks
Check/Replace Boost Pressure Control Valve (N75)
Check/Replace Boost Pressure Sensor (G31)
Check/Replace Turbo Charger


Do you have a boost gauge? what are you boosting to? I'm guessing you are pushing boost close to 30psi if your engine is getting that hot. can you put in stock mode or flash back to stock and see if the problem persists?

just my .02

[keithk831]

I don't have a boost gauge. I'm only at stage 1 for now. The problem is still there when I return to stock, but it's just not as pronounced.

I checked (visually) for leaks and didn't find any. N75 hoses are fine (I checked them when I replaced it). I'm about to take it to a shop to diagnose.

[jcun]

Keithk, how many miles did you have on the car before going stage I? I just recently purchases a 2014 a4 and am on the fence about upgrading the ecu.

[keithk831]

My car had about 52k when I did the tune just a couple months ago.


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[keithk831]

Well, i'm bringing this back from the dead again. I finally got my problem fixed!!!!

Took it to a reputable shop in West Jordan, UT that specializes in our cars. He spent a few days with it, took a bunch of logs with with a VAG-COM cable, and determined the hesitation was caused by a bad MAF sensor. It was throwing off my fueling and making me run slightly lean (but not lean enough to trigger a CEL). Also, my fuel pressure wasn't hitting it's target values. With the new MAF sensor in place, it's running smoothly.

Hope this helps someone else out.

[van462]

Than you for coming back with an update on the fix
That makes since for the overboost code. THe MAF told the ECU that less air was moving thru the turbo. The pressure sensor detected the "extra" air and since the ECU always trust sensors over hardware, it pointed to overboost. It would have been nice to have seen the long term fuel trim data, I am guessing it would be a farly high positive number, but as you stated just below the limits to prevent a lean code. The fuel pressure also makes sense, the ECU controls the fuel pressure regulator based off of its data. The maf reads low then the ECU doesn't command the regulator to feed as much fuel into the pump. if the fuel trim is also adding more fuel to meet O2 sensor requirements it would lower the pressure a bit more.
This is alos why I tried starting a basseline reading thread so that different data could be captured at different altitutes so that MAF issues would be easier to identify. it never caught on. No one want to gather data when their car is running good. Its a step that bites them in the ass later.