P0172

[phmichel]

Hey guys. Happy New Year.
Driving today and CVTz50 showed a little yellow warning flag saying "DTC: ENG". Ran the CVTz50 code scan and it showed P0172 (Fuel system rich - Bank 1). What's odd it that the ETC light on the dash never lit up.
2013 Rogue with 171k miles. I've never cleaned the throttle body yet but inspected it a couple months ago. It was a little dirty but not too bad IMO. MAP sensor was cleaned early last year and was not dirty. Any ideas? Thanks...

[VStar650CL]

P0172 is an unusual code. Vacuum leaks and other induction problems usually cause a P0171 lean code. P0172 basically means the ECM has run out of downward adjustment on the amount of fuel being injected. There aren't many things which can cause it besides leaky injectors, a bad front A/F sensor, or (indirectly) a bad rear HO2S. It's a 2-trip code, so it won't light the MIL until the ECM detects a second occurrence.

[VStar650CL]

PS - Also check for pinhole exhaust leaks in the immediate vicinity of the A/F or HO2S sensors. The easiest way to locate small leaks is to have an assistant block the tailpipe with a shop rag, the blockage will turn any pinholes into peashooters that will make an audible snapping or puffing noise.

[V6er]

or MAF "shows" waaaay too much air?
or there is some hole in intake after maf sensor...?

[VStar650CL]

The MAF way overindicating is a possibility, but a hole in the intake would cause underindication (unmetered air), which the ECM would treat as lean and adjust richer. In this case you have the opposite, your ECM thinks there's not enough air and is adjusting leaner. There aren't too many things which can cause that. Leaky injectors or high fuel pressure cause unmetered fuel, which the ECM tries to compensate by adjusting lean. An A/F sensor which is reading artificially lower voltage (richer) than the actual mixture can also cause it, as can a pinhole leak in the exhaust which skews the A/F readings.

[phmichel]

I think I found it. One of the tabs on the cleaner housing cap had popped loose. Would that be enough pressure loss to trigger this? And if the air filter was loose in the housing, wouldn't it run lean and not rich?

[VStar650CL]

The air filter is upstream from the MAF, so if the MAF is healthy it won't even care if there's no filter at all. Whatever goes through the MAF is by definition "metered" air. However, it's possible the loose filter let something get into the MAF, and that's a different story. The ECM is completely dependent on the MAF telling the truth, so all it takes is a piece of lint or butterfly wing in the wrong spot to cause a world of problems. Get some intake cleaner and spray through the MAF thoroughly.