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My wife's 2012 Audi Q5 has recently popped its check-engine light, and my scan tool reports:

  • "P2177 SAE System Too Lean Off Idle Bank 1"

She says that it appears to run & drive without issues and in the 30-min drive I took it on it seemed to behave fine to me, and it doesn't sound any different to before when idling or revving while standing still.

I have put 2 bottles of SeaFoam fuel injector cleaner thru it over the last week, but this doesn't appear to have made any difference - I can clear the code and it just comes back again.

What are the next most likely culprits for me to start checking?
Fuel filter? Fuel pump?
Any ideas most welcome ...

brhans
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2 Answers2

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A lot is required. Use a dealership level VW scanner, read the live data to deduce why the cylinder 1 is running lean, is it a fuel delivery issue, spark plug issue, bent air intake valve, ignition coil issue, or fuel rail nozzle issue. Could be any of these parts are malfunctioning, but you’ll have to find out why and either fix or replace. Sometimes the connectors or terminals are bad for electronics, so swapping the parts will not help. This suv needs full diagnosing, physical and computerised. I recommend you let the dealer diagnose it and you later work on the fix.

Since you possess a vcds, perhaps you can get on with it and see how far you can diagnose the aforementioned issue. I think you’ll be able to fix this, it is just a matter of time.

Lawyer Aidroos
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It appears that the root of the problem was the fuel pump - specifically the high-pressure mechanical pump on the engine and not the low-pressure pump in the fuel tank.

I had originally misinterpreted the diagnostic code "P2177 SAE System Too Lean Off Idle Bank 1" as Cylinder 1 being too lean (as did Lawyer Aidroos in his answer) which is why I thought that it might be a problem with the injector for that cylinder. But "Bank 1" does not refer to only "Cylinder 1".

After replacing the pump and clearing the codes I took it for a half-hour drive (which was enough to get all but one of the test readiness flags checked off so I could take it for its annual emissions test).
To my frustration, the CEL came back on again a few days later while my wife was driving, but within a day or 2 (before I got around to plugging the scan tool back in) it went back off by itself - so whatever it was seems to have cleared itself, and it's been good for about 2 weeks since then ....

brhans
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