CEL on an 02 Nissan Quest

[Wile E Coyote]

Quests have the same 3.3l as some Frontiers.
Alright, as you can expect, not much real tech on quest-specific forums, but this is moderately generic, so here goes.

CEL lights up, I get the codes for knock sensor and rear O2 sensor. Replaced the rear O2 sensor, and reset the codes.
Very soon, CEL is back, but now I can't read the friggin codes. The reader (Actron borrowed from Autozone) powers up, but never gets further than 'attempting to communicate". I know the data link connector gets power, as the reader does not have an internal battery. Getting power to/through all the fuses, and the van is not running in limp-home mode as one would expect a vehicle with a dead ECU to do. So, next thing would be to check voltage and resistance at selected pins on the ECU, right?

As lame as it sounds, I can't get to the ECU fully, as I can't get the dash around the glove box to come off.
What would any of you fellow stubbornly DIY folks do next in my shoes? (Spooky, no, you can't do that in my shoes ya freak)

 

[Gumby]

I would double check the reader first. It might also be good to get some data stream instead of just codes. If the O2 code that you're getting is a "HO2S B1S1 (or B2S1) too lean" (P1131 or P1151) then you could very well be experiencing a vacuum leak. That particular engine has a problem with the upper intake plenum leaking at the gasket.

If it is and you change it out, do the plugs at the same time. You can't get the rear ones out easily without removing the intake any way.

 

[Wile E Coyote]

I would double check the reader first. It might also be good to get some data stream instead of just codes. If the O2 code that you're getting is a "HO2S B1S1 (or B2S1) too lean" (P1131 or P1151) then you could very well be experiencing a vacuum leak. That particular engine has a problem with the upper intake plenum leaking at the gasket.

If it is and you change it out, do the plugs at the same time. You can't get the rear ones out easily without removing the intake any way.

Thanks for the help. My code was for the O2 heater circuit. You aren't kidding about some of those plugs. I did em at around 60k miles, and it's just hit 100k, so it wouldn't hurt. I'd also be able to do the knock sensor with the intake off. Usually however, the knock sensor isn't bad, and thrown codes tend to come from other primary reasons, ya know.
As far as a data streaming reader, I'll have to look into that one. I'd rather not spend the $ required for a good reader, as I just dropped $11k on other crap last month. This is one poor coyote, and Acme done dropped my line of credit.

 

[Gumby]

Not too often the heater circuit code is anything but the HO2S.

 

[Wile E Coyote]

Not too often the heater circuit code is anything but the HO2S.

Agreed, which sparks my interest further as to what the latest code (and inability to read) is all about. It's been on long enough, and came back on after resetting (batt disconnect) that it's likely not a simple loose gas cap syndrome.
Thanks for the continued attention.
It's gonna bug me long enough that I'll have to go get my own code reader. That'll have to wait, I have to fix the clothes dryer today.

 

[35inchoverdrive]

Don't rule out a malfuntioning code reader(as mentioned above). I was trapped in the parts buisness for a couple of years, and we had 2 or 3 code readers crap out. I never got the "attempting to comunitcate," but they did often fail to power up. Drive to the next Autozone(probably .5 miles away from the one you got the code reader) and get the sales drone to pull the code with the store scanner. Be sure not to mention anything about having trouble with another scanner, as most of them don't deal well with 'additional information'. I only say that, because I was trapped in a store with them.