O2 sensor

muddog · August 12, 2003

my truck:

1996 chevy 1500

4.3 v6 78k miles

auto

the problem:

the SES light came on and I got the codes read at Auto Zone. One of the codes was 172 I think, I looked it up online and it said "P0172 System too Rich (Bank 1)"....so should I just replace the oxygen sensor? And isn't bank 1 the left bank? Or is there something else that I should do? Thanks for all your help

frdfandc · August 12, 2003

Something is causing you to burn too much fuel. It does sound like an O2 problem. I would check out your plugs to see if they are starting to get fouled with fuel. And yes, bank one will be the engine bank on the drivers side.

CMNTMXR81 · August 15, 2003

I agree, it may be something else. HOWEVER, if this is the upstream O2 sensor (pre-cat), the PCM requires that it switch a certain number of times in order to maintain aas close to a stoich ratio as possible. IF it does not switch as much, or flat out is not responding, the PCM could be trying to compensate for it.

A way to tell if you sensor is bad is to hook a scanner to it select the O2 sensors to read the mV readings, switch the key on, and watch what happens. Within seconds (if not sooner) the O2 sensor should either jump past .700mV or drop below .200mV and continue to go down. If not, say if it remains stagnant in the .500's or .400's that may be a sign of a bad (slow responding) O2 sensor.

But I would find out first if this is the root cause. Otherwise, you'll end up putting in a new one, only to screw the new one up because you didn't fix the problem.

BDBWTE · August 16, 2003

I agree, it may be something else. HOWEVER, if this is the upstream O2 sensor (pre-cat), the PCM requires that it switch a certain number of times in order to maintain aas close to a stoich ratio as possible. IF it does not switch as much, or flat out is not responding, the PCM could be trying to compensate for it.

A way to tell if you sensor is bad is to hook a scanner to it select the O2 sensors to read the mV readings, switch the key on, and watch what happens. Within seconds (if not sooner) the O2 sensor should either jump past .700mV or drop below .200mV and continue to go down. If not, say if it remains stagnant in the .500's or .400's that may be a sign of a bad (slow responding) O2 sensor.

But I would find out first if this is the root cause. Otherwise, you'll end up putting in a new one, only to screw the new one up because you didn't fix the problem.

YEAH!

AZ1500 · August 17, 2003

Have you increased your airflow lately with a higher flowing maf or throttle body. I've seen some pcm's throw this code because of higher airflow mods which makes the pcm think it needs to richen the mixture.

CMNTMXR81 · August 18, 2003

With our TB's being electronic, I have not seen aftermarket larger units (that doesn't mean that there may not be any), so you'd have to home port yours which could also lead to potential codes thrown. Although this would nto be the case on his 96.

Rotorwrench · August 18, 2003

You can allways try swaping the O2 sensors from one bank to the other and see if the DTC chages to the other side too.

CMNTMXR81 · August 18, 2003

That depends. On some vehicles, the plugs are different. One is a 4 pin square pig tail and the other is a 4 pin flat pigtail. Some vehicle's both are the same though.

dreamer1q · September 17, 2003

Pull the sensor and swap it to the other bank. See if the problem follows the sensor. If it does replace it. If it dosent, start looking for nicks in the wiring. The O2 sensors are run at a certian Ohm. If that is disturbed, it will cause the O2 to tell the computer to dump more fuel, thus fouling the O2. I have chased this problem on my Camaro. At the same time, O2's are just like spark plugs, they wear out. Sometimes they do need to be changed.

Q

CMNTMXR81 · September 18, 2003

I have not been under a 4.3L truck in awhile, but I don't recall them having the dual bank setup for 02's similar to the F-Bodies, so switching B1S1 to B2S1 as you suggest may not be an option.