Fault Code P2198?
 

On our 2005 MPV, 78K miles, the engine lite came on, stayed on for a few minutes of town traffic, then went off. When I got home, I hooked up my OBDII unit and picked up stored code P2198 plus a bunch of "pending" faults around the emissions systems. I googled the code and came up with LOTS of possibles, but those were also for lots of different vehicles. Does anyone know a more specific diagnosis when applied to a 2005 MPV?

Kinda hate to start blindly replacing parts here, and the car needs to pass CA smog real soon!

Thank you!

I don't have access to MPV workshop manual, but I do have access to a V6 Tribute manual.

DTC P2198

Lack of HO2S-21 switch, sensor indicates rich

DETECTION CONDITION

• The PCM monitors HO2S-21 signal switching during over lean condition at PCM terminal 87. If the PCM no longer detects switching for calibrated amount of time, the PCM determines that HO2S-21 cannot switch from rich to lean.

POSSIBLE CAUSE

• Electrical components malfunction
- Short to power supply circuit in wiring between HO2S-21 terminal 4 and PCM terminal 87
- Water in harness connector
- Corrosion or poor mating terminals and wiring
- Damaged HO2S-21
- Damaged PCM
• Fuel system malfunction
- Excessive fuel pressure
- Leak in fuel injectors
- Leaking in fuel pressure regulator
- Vapor recovery system
• Intake-air system malfunction
- Vacuum leaks
- PCV system malfunction
- Improperly seated engine oil dipstick
• EGR system malfunction
- Leaking gasket
- EGR valve stuck
- Vacuum leaking at EGR valve diaphragm or EGR solenoid valve
• Base engine malfunction
- Oil overfill
- Cam timing
- Cylinder compression

What were your other codes? The O2 code could be the triggered by other failures and not necessarily be the O2. The other codes may help in getting you a little closer to the root problem. You'll most likely looking for something to cause the engine to run rich.

P2198 code diagnosis progress (2005 MPV)
 

So here's what I've got to date. In response to the questions about the other codes, they are "pending codes," which usually clear themselves while driving if the fault that set the code was actually fixed. At least that's been my experience. They included cat monitor, evap system monitor, O2 sensor heater monitor, and EGR monitor. I have no idea how essentially a vacuum leak would have triggered all of those, but since they show only as "pending," I'm hoping they'll clear after the obvious issue is take care of.

What I did find out for sure is that the pcv hose assembly was toast. It had a hole melted in the elbow right at the PVC valve, and the elbow at the back of the engine (what a sweet thing it is to disconnect that!) was collapsed to the point where it was almost completely closed off.

Since there were some comments on this forum about that hose assembly being a dealer part, I called (with a lot of trepidation; I loathe having do do business with auto dealers at any level) and was told the part was not in stock, but they would order it in for me. The part was $49.65 plus $12.00 shipping. OK, so I went on good old Rock Auto and the had it for about $10. It will be here in a few days.

I am so hoping that this will fix the issue. This has been a remarkably dependable vehicle. Only repairs to date (78K miles) have been coils, plugs, and the cooling fan temp switch assembly.

I'll post the results when I get the parts installed in a few days.

Thank you, all, for your assistance!

Awesome, glad you found it. Surprised there wasn't a lean code in the mix. Mazda did a revision on that hose that significantly reinforced the elbow to avoid reoccurrence of collapse. I'm not sure if the aftermarket hose will have that. If it doesn't, you will want to check it periodically to make sure it doesn't happen again.

Not fixed just yet; waiting for parts.
 

I'm still waiting for the parts which should be here tomorrow. I also used my phone to take some nice, clear photos down behind the engine where that PCV hose enters, and unfortunately, the elbow fitting there is collapsed, too, so I'm going to have to figure out how to work the clamp that secures it. So far I'm only succeeded in getting a bunch of scrapes and bruises on my arm. I was going to leave that fitting and I hoped that it was just the melted-through elbow on the PCV-Valve end. I may end up removing the intake plenum again. Just did a few months ago to replace plugs and coils. Why do I like old, RWD cars with the engines installed in the correct direction? :)

I'll post the results when it's all done.