[470MR10]

I know this is more of a mechanical maintenance question, and i did post there, but just wondering if someone has a dedicated track car and bypassed the emission codes / CEL.

TL;DR - I live in a state that doesn't have emissions laws/doesn't check emissions. Is there a reversible bypass for CEL on for emissions codes? (mechanical or coding)


Note: All codes were read using Veepeak OBDCheckVP01 and OBD Fusion for IOS by OCTech.
Codes were looked up on the following website, as it was the most informative and consistent I could find for the codes I have been getting:

https://bimmerguide.de/p-code-fehler...gstabelle-bmw/

(No, I don't speak German, so I translated through google)


In January/February, my CEL came on and I got the following code:
• U029F Loss of communication with tank ventilation system leak diagnosis control unit

in combination with any of these following codes:
• P147D Tank Vent System Leak Diagnostic Module Circuit - Malfunction or open circuit
• P147E Tank Vent System Leak Diagnostic Module Circuit - Low
• P147F Tank Vent System Leak Diagnostic Module Circuit - High


In late March (while I was waiting for an open slot at a well recommended mechanic), the check engine light went away. Occasionally it would pop up if I parked under a roof (e.g. in a service garage for tire rotation, or in a parking garage anywhere but top floor.

In mid June, I got a stage 1 tune installed at Dinan, and on the 5 hour trip home, drove through 3 or 4 massive rainstorms. The CEL came back on and stayed on with the following two codes:
• U029F Loss of communication with tank ventilation system leak diagnosis control unit
• P147D Tank Vent System Leak Diagnostic Module Circuit - Malfunction or open circuit


To be sure I was looking in the right place with the DMTL, I unplugged one of two sensors on fuel vent valve assembly and received the following code in addition to the U029F and P147D:
• P0444 Tank Vent System Purge Valve / Tank Vent Valve Circuit (Bank 1) Open circuit

I plugged the sensor back in, unplugged the other sensor, and the P0444 code was replaced by the following code in addition to the U029F and P147D:
• P11C6 Tank Vent System Differential Pressure Sensor Circuit - High

I plugged second sensor back in, unplugged DMTL, and received no additional codes aside from the U029F and P147D.


So in early July, I replaced the leak diagnostic pump. However, the check engine light remains on with the following two codes:
• U029F Loss of communication with tank ventilation system leak diagnosis control unit
• P147E Tank Vent System Leak Diagnostic Module Circuit - Low


After a month of trying again to get a slot with that mechanic, he finally had availability that I could stop in for a quick diagnostic. He read the codes, agreed that it was the DMTL, and suggested a few things. One was that I may have gotten a faulty part as my replacement, another was that he could do a smoke test, and finally that it could be one of two wires shorting to ground.

If checking the replacement DMTL and the smoke test both turn up nothing, then he can get under the passenger rear quarter panel and check the shorter length wire. If there are no problems there, he won't bother checking the long wire, but instead will just run a new wire from the computer back to the DMTL.

Assuming any of these things work, I already threw $200 at this CEL, and it looks like I'm about to throw another $300 to $500 or more. And I live in a state that does NOT do emissions checks, so I'm paying out a few hundred just to turn of a POS light bulb. And what's worse is it could still come back on any time for another trigger happy emissions related sensor (this has been my luck with other cars).

If I lived in an emission checking state, I'd pay for the maintenance and shrug it off, knowing that I was paying all this money to satisfy a state regulation. But as it stands, the money I'm shelling out has zero regulatory impact. And as I've come to understand, the only thing the CEL does by itself is tell me emissions problems. As I understand it, iDrive and my OBD reader have me covered if any real mechanical issue was to arise.

All of this is to ask, is there a fuse I can pull, or a setting I can change to make this eyesore CEL (and any other emissions code that is of no consequence in my state) go away? I only want something reversible, in case my state passes emission standards laws, I move to a state that has them, or when I sell the car.

I don't want to break any laws, I just don't live in a state where these laws exist, and turning off a bulb seems like wasted money.

[cooolone2]

Why don't you just smoke test your car and fix the evap leak?
Sure, a PITA, but doable...

It seems you're trying everything but...

And shotgunning parts at a problem is not how to fix it either. You're taking the long hard road! Especially dropping a tune while there is a physical malfunction present.

I HATE evap leaks as they can be anywhere, a vac line, a sensor, a small, unseen hairline crack in something... But SMOKE will show what, where. That's it! Just be patient and test a few times to make sure that's where the leak is.

If you don't want to do it, take it to a mechanic and they'll smoke test it and tell you where the problem is. Then if "you" want to fix it you can. That is easier than finding the leak yourself. It's my opinion that this is a leak as you've already played with the parts...

Good luck!

[470MR10]

thanks for the quick feedback.

i have an appointment with the mechanic on thursday. he’ll do a smoke test, but he already seemed certain it was a grounded wire, which i’m afraid means removing body panels.

i had second thoughts about tuning with this going on but
1) the code had been clear for 2 months before
2) the code was only emissions related and had no effect on engine performance
maybe not the most prudent decision, but i’d like to think i didn’t make it with reckless abandon.

and on the similar point of misguided maintenance diy: with all 4 codes specifying the DMTL, i figured that was a reasonable wager and an easy part for me to replace before dropping my car off with the mechanic for the better part of a week while i borrow my in-laws mazda 3 (a solid commuter, but a less than engaging drive)

please understand i am not trying to counter your points. i’m just wanting to mend my wounded pride and defend my decisions XD

but again, solid advice and very much appreciated. having patience is not always easy, and so a friendly reminder to is always welcome

[470MR10]

for those who care, the mechanic found a broken wire going to the evaporative unit. i assume this not the plug that connects to the leak detector pump as i checked those wires well while under the car and replacing that pump. he sent a pic: