System Too Lean codes

A6 All/ S6 All
#1

I recently replaced the Throttle Body 6-pin connector (Bank 1/Passenger side). The car seemed to run fine for awhile, but now I’m getting the following codes for the first time:

  • P0171, P0174 System Too Lean Bank 1,2
  • P1075, P1077

How can I tell if this is related to the TB connector or a completely new issue?

Note: I’ve also been getting a persistent P0023 - “B” Camshaft Position - Actuator Circuit/Open Bank 2 fault which seems to be related to rough cold starts. Despite all these faults, the car engine runs very smoothly once it reaches temp.

Why the random codes/misfires–what is the cause?
#2

I went back to check the 6-pin electrical connector to the passenger side TB. It seems to be fine, but I also noticed the following issues:

There is a square vacuum hose lock ring that is broken. It connects to the lower of 2 outlets from the intake hose to the passenger-side TB.

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I also noticed a slight fuel leak on the the passenger-side HPFP at the electrical connector

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Could either of these problems be the source of the fault?

#3

I’m down to just these intermittent codes:

Basic OBD2:
P0171 (pending) - System Too Lean Bank 1
(confirmed) - System Too Lean Bank 1
P0174 (pending) - System Too Lean Bank 2
P1075 (pending)
(confirmed)
P1077 (pending)

I replaced the bank1 HPFP because it was obviously leaking, but held off on the bank2 HPFP because it was only occasionally “weeping” from the electrical connector side. Are there any other places to look before I get another HPFP?

BTW, the P0023 fault seems to have been fixed by securing the wiring harness on both ends with new zip ties.

#4

I had that same lock ring connector break on mine. Threw on some c clamps for good measure.

When I purchased the car, the throttle body had a hairline crack where the fastener that mounts to the Y plenum goes. Check those VERY carefully.

Also, I’m not sure a crack in the PCV breather line will throw a lean code, but mine was crack and brittle at the PCV end.

#5

I know its daunting. If you dont have a means to verify leaks with a smoke machine, you’ll need to systematically inspect nearly all the connection points on this diagram:

#6

I recently got rid of those same codes by replacing the PCV - again. I had replaced it about 4 months prior but with a cheapo from eBay. It was the only non OEM part I’ve put on the car and after reading this post I decided to replace it with an OEM one. May not apply to your situation here exactly but thought it was worth mentioning.

https://forums.ross-tech.com/index.php?threads/19440/

#7

NTYMI, I do have one of those hairline cracks by the bank2 TB, but it’s been there for more than a few years. Also had a gasket leak on bank1 that was replaced last summer. I used some RTV as a stopgap at the time and it seems to work. It might be good to try that again.

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