2500 8.1

pouly · November 1, 2001

was under truck today why is there 2 oxygen sensors

Shaners · November 1, 2001

pouly,

I only have the 6.0L in my HD, but I have 2 cat converters. I'm guessing the computer senses emmisions from each bank of cylinders...

raventai · November 2, 2001

I assume your 8.1 is identical to mine and the exaust dose not combine until the muffler (after the cat so to late for O2 sensor) to get an accurate reading u need both banks as Shaners said

chevy4x4trucks · November 2, 2001

my 4.8's got 2 cats on it

MemphisDoug · November 2, 2001

I might be wrong but I think if you look closer you might see that there are actually 4 oxygen sensors. There is one for each side of the engine both before and after each of the convertors.

CMNTMXR81 · November 2, 2001

Any GM engine after 1996 (1995 in California) runs on a system called OBDII (On Board Diagnostics System 2). This system monitors your emissions before the exhaust enters the catalytic converters and then after the catalytic converters.

The Purpose for this is for the PCM to see that the Cat's are working. The exhaust going into the cats should have hydrocarbon readings in the high .800's to low .900's in PPM (Parts Per Million) at WOT (Wide Open Throttle). The exhaust exiting the Cats and hitting that second set of O2 sensors should be less than the pre-cat readings 90% of the time. If not, it triggers a DTC (Diagnostic Trouble Code) therefore setting the SES (Service Engine Soon) light on your dash.

So if you have one catalytic converter, you'll have two O2 sensors and if you have two catalytic converters, you'll have 4 O2 sensors.

They are labeled as follows;

Driver's side = Bank 1, sensor 1 (before cat), sensor 2 (after cat). More commonly acronymed as B1S1 and B1S2

Pass side = Bank 2, sensor 1 (before cat), sensor 2 (after cat). More commonly acronymed as B2S1 and B2S2.

Other common measure taken off of the O2 sensors are the short term and long term fuel switches where the PCM tries to trim or richen the fuel mixture in both short and long term tables according to the readings generated from the O2 sensors.