Lean codes on both banks JHM 93 car

B6/7 S4/RS4
#1

Hey guys, a friend of a friend of mine recently picked up an 05 B6 tip S4. The car has 44k miles on it or something like that. He bought the car with a JHM tune on it as well as Fast Intentions catless downpipes and cat back.

He contacted me because he has a check engine light. The shop he took it to says he needs a new ECU but they’re an APR dealer so they probably are biased towards the idea of selling him an APR tune. Its been a while.since I’ve had my S4 so hopefully you guys can help me lead us in the right direction.

Lean codes on both banks on a JHM tuned car seem a bit odd to me. I seem to remember all JHM tunes being catless ready. Hopefully this is just a case of sensors failing after going catless because I know that happens a lot too.

He has had the car for a couple weeks and says that he has used 93 octane from a few different stations so we could probably rule out fuel quality.

Here is the VCDS printout.


http://i183.photobucket.com/albums/x59/joec1992/Mobile%20Uploads/imagejpeg_0_zpsuobayrgn.jpg

#2

check vac lines. I got lean codes from a boost leak on both banks.

#3

Double check that the 5 mm allen bolts for the intake manifold are tight. Very common and very easy to check.

#4

Great info already, I also got a lean code on my S4 because the DP flange was not completely sealed and I believe was letting false air into the system.

It’s weird how fucking shitty shops say stuff like…“you need a new ECU” How about you troubleshoot the fucking car based on the matrix in the Bentley manual.

SAE VAG Description
P2098 18530 Post Catalyst Fuel Trim System Too Lean Bank 2

Fuel Trim, Post Catalyst, Too Lean

Check oxygen sensor and oxygen sensor control behind catalytic converter
Intake system for leaks (false air) checking
Oxygen sensors and oxygen sensor control before catalytic converter checking

SAME for 2096

#5

Thanks guys

Wouldn’t the primary sensors monitor air/fuel? Seems weird for the secondary sensors to monitor that.

I’ll check the intake manifold bolts. Completely forgot about that and I’d bet that is it since it would cause lean on both banks must likely.

#6

Yeah I’d expect the primaries to trip for air leaks. One important note, the O2 sensor measures O2 concentration only. Afr is correlated, hence why incomplete combustion (eg bad coilpack) shows lean codes, O2 concentration is higher than usual b/c the O2 is elemental and not reacted with C/N. The sensor itself functions via an oxygen fuel cell.

#7

Exactly. What a joke.

#8

Lots of great advice. Since its both banks check pretty intake and pcv system. The codes came at cruising speeds. So there is a chance it happened after a long trip. First start with clearing the codes and checking to see how quickly the codes come back.