I have been getting a P2000 check engine light on my '05 Honda Civic Hybrid and I have two questions:

I am not sure what the code means. ALL (4) of my scanners (An Auto Xray, CarCode Serial Logger, PLX Kiwi Wireless and DashHawk) all say it means NOx Trap Efficiency Below Threshold. Which directs me to look at the O2 sensor outputs which are alarming...voltage levels on O2 sensors are high for rich, low for lean. Sensor 2 is between the cats, Sensor 3 is aft of the second cat. My second sensor is chronically higher voltage (by 50mv or so) than my forward sensor. When I warm the cats up (spirited driving, etc), it goes way beyond that.

Now the OBDII reports a short term fuel trim capability for both the second and third O2 sensors and the second fluctuates mildly between -2 and 2, probably normal. The third is pegged at 99%.

So I'm guessing due to it registering more rich than the two in front of it, that it has failed and that the failure mode is to do something that the computer will see and flag (like fail rich). The cat isn't rattling or anything so I don't suspect it at this point.

The rub in this while dilemma is that a few places online show a P2000 code as a 'Hybrid Battery System Voltage High' code.

Is anyone here a shop tech who can help me out to either validate my assumption here about the tertiary O2 sensor or verify/deny the P2000 code as a 'Hybrid Battery System Voltage High' issue?

Thanks,

Jason

 

The P2000 code description is NOx Adsorptive Catalytic System Efficiency Below Threshold. The third O2 sensor should be pegged lean (if the cat operating correctly) therefore making the STFT (short term fuel trim) for the third sensor be at 99%. So that part is normal, however, the first cat which breaks down the NOx into nitrogen and oxygen seems to have failed which set the code. So with all that said i'm afraid that you have to replace your first cat.

 

Ahhhh, good point. The 99% would be pegged lean indeed if we look at this using the % system that a primary O2 sensor uses. But why the higher voltage numbers on the third vs. the second sensor? That would indicate that the second sensor is seeing less fuel than the third. And my local stealership (gotta get the right guy on the phone) shop manager says 4 out of 4 techs say they fix that code with replacement of the secondary cat. Took him three days to get back to me, but he was astoundingly helpful knowing I was going to fix it myself.

I know I can get the second cat for a very reasonable price...

97, what made you think the primary was the NOx scrubber??

Jason

 

Ya thats my bad, the second cat is the NOx adsorptive cat. I was thinking of traditional cars having the NOx reduction catalyst before the HC and CO reduction catalyst. The civic hybrid kind of does it backwards though. So the second cat is indeed the NOx reduction catalyst.