car is an 04 mazda 6 v6 with 139k.
I've been throwing lean codes P0171 and the occasional misfire P0300 last week. I had a dealer tech install plugs and a PCV valve yesterday. Now, the next morning. After having driven ~200 miles I"m getting a CEL again.
p0171 and p0174, system too lean
p219702, sensor signal stuck lean.
From the driving I did last night, the car is definitely running smoother now. I was hoping to go to WI this weekend, but I can't risk being stuck in the middle of nowhere if this turns out to be serious.
I used a PCV from an 05 because I heard they were designed better, could a slightly larger PCV be causing these issues?
Any help is greatly appreciated.
Clear codes and retest?
You let someone else work on your car, perhaps they are trying to up-sell?
I would say the lean code is probably unrelated to the PCV since it was present before and after the new PCV. But just in case - did you change the PCV hose when changed the valve? Often times the old style PCV hose on these cars collapses and tears, and it's possible yours is worn enough to cause a lean condition. Also I don't think the old style hose fits the new style valve. I used the new style valve and hose when replacing mine and had no problems.
Is it possible you have intake leaks? Have you checked the air filter housing, ducting, etc for correct connections and worn parts?
I should add, the cracked/leaking PCV hose is not always obvious. It's often on the elbow and kind of easily concealed. With the car running you can poke at and flex the PCV hose and see if it changes sounds. If you didn't replace the hose I would strongly suspect that first.
Vacuum leak is the most likely cause, if its otherwise running correctly. Having both 171 and 174 imply something common to both banks. Check the hose from the air flow sensor to the throttle body. Spray some wd40 around at gaskets and hoses with the engine idling. If the idle speed changes, focus in on where you are spraying. Does that engine share the Fords badly sealed intake runner throttle (IMRC) shafts?
No leaks, start looking at MAF or fuel pressure
The lean code applies whenever the ECM has reached the limit of fuel enrichment. Something has been causing it to run lean (in reference to how the O2 sensors see things) so it adds more fuel. If the LTFT (long term fuel trim) reaches a threshold (let's say 20% fuel enrichment) and it doesn't solve the issue, it trips the code. So... either the engine is actually running lean, or the O2 sensor isn't working correctly.
P2197 refers to the Bank 2 sensor 1 (upstream) O2 sensor.
First things first: Check the intake boot for tears. Its pretty common for those to rot and get a tear in the bellows. With the car running (and all the pretty engine covers off) start spraying short blasts of brake cleaner at the MAF, hoses, where the intake meets the heads, etc. If any of the places you spray cause a change in the idle, you have a vacuum leak.
Check the wiring to the bank 2 upstream O2 sensor. If there is a faulty wire (particularly on the heating circuit) it will cause this code.
Check fuel pressure to make sure its within spec.
I think you would hear an exhaust leak in the manifold, but that would almost always cause this code.
If you don't want to throw expensive parts at it, try a junkyard O2 sensor to see if it changes/helps/eliminates the issue.
Bottom line, either the sensor is bad (unlikely since there are other misfire codes associated with it) or you have a physical failure causing A) too much air or B) not enough fuel.
Streetwiseguy wrote:
Vacuum leak is the most likely cause, if its otherwise running correctly. Having both 171 and 174 imply something common to both banks. Check the hose from the air flow sensor to the throttle body.
On my '03 Mazda6 V6 it was a tear in the elbow from MAF to TB. It was torn on the inside of the bend, from oil change jockeys leaving it attached to the air box lid and bending it way out of the way to show the PO how dirty his air filter was. I was setting both lean codes plus the occasional misfire.
It looks like my issue is the 'temporary' piping I used to connect the CAI to the TB, that I never got around to finding a proper tube to use. The car runs fine with the CAI hooked directly to the TB with some silicone tubing.
