2003 Ford Crown Victoria
V8 Engine
Dual exhaust
2 cats & O2 sensors per side

Since some time last year I've been getting an error code throw up, with seemingly no regularity:

P2197 - O2 stuck lean - Bank 2 Sensor 1

First thought was to replace the sensor, so that's new but didn't fix the problem. It doesn't happen much when it's hot and dry, primarily when it's cold and/or damp out.

I recently picked up a bluetooth OBD-II live scanner, and looking at the values as I drive, I've learned that, when it does happen, the O2 voltages are pretty much normal, though they'll kind of "stick" on B2-S1 to a number (different each time) whereas B1-S1 will fluctuate normally. I've seen anywhere from .06v to .94v

At the same time, the short-term fuel trim will lock even tighter to a number, and stay that way until it all clears. Most common is 32.8%, but there is some variance from about 30% - 55%.

It'll start normally, then within about 10-30 seconds lock onto these numbers, stay that way for about a minute, then return to normal ranges for both voltage and trim. If the car is started cold then it won't throw a code, but if it's still warm then it will often trigger the MIL and store the freeze-frame data.

Any ideas on what's actually wrong, how to fix it, or more diagnostics to do?

My #1 thought is a vacuum leak somewhere, and I have an idea of which chunk of hose it might be, but I haven't had a chance to find a new one to replace it with. My other thought is the computer having some values stored wrong that I would need to reset (just disconnect the battery). I only thought of this one a day ago and haven't had the time to do it yet and still go on a long enough drive to relearn shift points.


From everything I see in this paper, it seems that it may be related to a vacuum leak.

tl;dr - Check your vacuum lines and make sure none of them are cracked.

P2197 Page 1 P2197 Page 2 P2197 Page 3

Here are some more ideas from here:


Lack of HO2S-21 Switch, Sensor Indicates Lean Detailed Description A heated oxygen sensor (HO2S) indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time.

Possible Causes:


  • Short to VPWR in the harness or HO2S.
  • Water in the harness connector.
  • Open/shorted HO2S circuit.
  • Corrosion or poor mating terminals and wiring.
  • Damaged HO2S.
  • Damaged powertrain control module (PCM).

Fuel System:

  • Excessive fuel pressure.
  • Leaking/contaminated fuel injectors.
  • Leaking fuel pressure regulator.
  • Low fuel pressure or running out of fuel.
  • Vapor recovery system. Induction System:
  • Air leaks after the mass air flow (MAF) sensor.
  • Vacuum Leaks.
  • PCV system.
  • Improperly seated engine oil dipstick.

EGR System:

  • Leaking gasket.
  • Stuck EGR valve.
  • Leaking diaphragm or EVR.

Base Engine:

  • Oil overfill.
  • Cam Timing.
  • Cylinder compression.
  • Exhaust leaks before or near the HO2S(s)
  • If it's just on a single bank, vacuum leak is the first place to look for sure. Oct 31 '12 at 16:38

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