'97 FS Chevy failed emissions

[SCCA1995]

Ok, so I have a 1997 Chevy 2500 LD (6-lug 2WD) Cheyenne with the 5.0L Vortec V8 with the 4-speed auto. It doesn't have a "Check Engine" light on when I went to the vehicle inspection station. Once there, the guy said & printed on the page that it shows *No MIL at key-on/engine-off*. He had to start the truck to attempt to read the computer & it registered a P0141 O2 sensor heated circuit malfunction in Bank 1, Sensor 2. I'll admit, I know the basics about the OBD-2 setup, but I'm wondering if there is a common repair for the trouble code (readout makes it seem like a sensor replacement--simple, maybe not cheap). Also, is there something simple that someone else could have done to disable the MIL at the key-on/engine-off cycle? I know what the k-o/e-o means, because my 2 previous GM cars with OBD-2 could be read without starting the vehicle. I did just buy this truck on Ebay, so this explains how something might not throw a check engine light (someone trying to sell it without raising an issue). I got the truck cheap enough that a minor amount of investment may not hurt me.

[MrCritical]

Most likely a bad o2 sensor or catalytic converter. Ck wiring going to sensor to be sure, though.

The simple thing someone could have done was to pull the bulb in the instrument cluster so you don't get the ck engine light.

[TheBUC]

The code posted tells me you have a bad O2 sensor, heated circuit is not working. This will cause your fuel milage to drop alot. Replace it and clear the codes have a good long drive to get some cycles in your ecm and then get it tested again.

[SCCA1995]

I spoke to a mechanic who said the same thing. I'll check that after Let's Make a Deal goes off. Thanks.

[68haywagon]

The p0141 is the code for the downstream O2 on the passenger side. This sensor will not effect fuel economy, it is there to make sure the catalytic converters are working correctly. Simple replace, clear, and drive.

[SCCA1995]

Passenger's side? I thought the driver's side cylinders would be bank 1. Just by crawling underneath it, I can only find one cat (& 1 after cat O2 sensor). My county requires emissions testing, so no computer codes are allowed. Otherwise, the truck drives fine.

[TheBUC]

It is the left side, drivers side, bank 1 and sensor 2 is the back O2 sensor. When any of the O2 sensors brings up a code your fuel milage goes south.

[SCCA1995]

So far, I still only see 1 catalytic converter. The pipes from each bank of cylinders merge ahead of the 1 cat. I have only seen 1 O2 sensor after the cat. Unless there is a second cat hiding under there, this should point to the only O2 sensor behind the cat. I have a new sensor & I'll double check for more than 1 cat. Unless someone has some kind of diagram to show a second cat.

[SCCA1995]

In case anyone else has a problem like this, I found the 4th O2 sensor. It's still only got one cat converter, but 4 O2 sensors One is located in each pipe coming from the exhaust manifolds (B1S1 & B2S1). Then there is one behind the cat which is actually B2S2, which I replaced. After replacing it & clearing the codes, it came back. So today, I went back under & traced the wiring thinking I may have a broken wire. When I traced the wiring harness up to the B2S1, I saw another O2 sensor within 6 inches. This must have been the elusive B1S2 I hadn't seen yet. After replacing it, I've cleared the codes again & I will see if it comes up again or if it's finally gone. Damn EPA making cars & trucks use so much more crap.