service engine soon light

I recently purchased a 2000 S-10 Blazer that had a problem with the fuel guage. I replaced the sending unit (pump & sending unit are all in one) with a used one from the bone yard. That seemed to fix the guage problem. Now the service engine light is on and seems to be running rich. Been this way for 2 weeks now. The daughter drives the vehicle, so I had her swing by Auto Zone to get a read on the diags and was told that the o2 sensors are bad. I suspect I need to go down there myself to get the exact code. In the mean time is it possible that the fuel pump / sending unit replacement is in any way related to the 02 sensor problem?

Probably not.

Tell the Autozone guys to stop being so general and to tell her the actual code.

There are 4 O2 sensors on that vehicle.

You need to know the actual one that is causing the problem.

OK I got the codes, there were 4 codes and each one of them was in there twice. The codes were P0172, P0175, P1133, P1153. I understand that the P0172 & P0175 are right & left bank to rich diags which I suspect are precat o2 sensors. Any idea what the P1133 & P1153 diags are.

Here are the codes, they are interrelatied.

P0172 = Adaptive System too Rich (Bank 1)
P0175 = Adaptive System too Rich (Bank 2)
P1133 = O2 Sensor Fault - Insufficient activity (Bank 1 , Sensor 1)
P1153 = O2 Sensor Fault - Insufficient activity (Bank 2 , Sensor 1)

Both O2 Sensors in each manifold are bad.

One thing I need to ask, was the sending unit from the same year and model of truck?

Just so I understand, one sensor (or two sensors) in each manifold? I looked & only saw one on each side.

The fuel pump / sending unit appeared to be the same unit. If there was any physical difference it would've been slight & I didnt catch it. I could send an email to the place I bought it from and verify the year and model.

Lemme break it down for you.

You have four O2 sensors in your truck.

One in each manifold coming down from each side of the engine
One in front of the CAT and one behind the cat.

the two in the manifolds are the ones that are bad.

Awesome! Thanks spelling it out for me.

Is there reason for concern about the make & model of the vehicle the new / used sending unit came out of?

Yes, it does make a difference.

If it is from a different vehicle with a higher fuel pressure, it could cause this also.

What year, make and model did it come out of?

I'm told the replacement fuel pump is out of a 2000 Brevada. They assured me the parts are identical. Anyway to prove or disprove that?

Did you change the sensors?

Well, I put in both sensors prior to the cat. Drove it around the block about 2 miles and nothing changed. I put the original sensors back in, maybe theyll let me return 'em. I'm thinking about putting my original pump back in as this problem (check engine) didnt start till I put this new/used pump in. It appears that the sending unit can be swapped. I have it off except the wires at the feed thru connector. I'm thinking about cutting the wires & soldering. Will that hold up to the gasoline?

Did you reset the computer after you swapped the sensors?

No I didnt think to do that. How do I do it?

You remove the negative battery connection from the negative battery terminal for 10 minutes.

You ALWAYS reset your cmoputer when you do sensor swaps.

I reinstalled the new precat sensors and reset the computer this time. it took about a day but the light came back on. One more observation, the fuel pump is making a high pitched whining noise. It is not really noticeable unless the door is open.

Wierdest thing I've heard in a while. Unless I'm mistaken the fuel pressure is regulated at the fuel injector assy so the pump is not an issue unless it was a low pressure pump, not likely. Are these three wire O2 sensors? Getting power to them? Check fuses?

The sensors have four wires. Which wire should I expect to have voltage on it? If I remember what I've read on other posts that is a very low voltage, like a few hundred millivolts, yes?

I just did some research on your problem and the bank sensors reading rich is usually due to a MAF sensor going bad.

Have you descreened your MAF or installed a new K&N filter lately?

No, I havent owned the vehicle for long. It looks like I need to go & pick up a service manual as I couldnt tell you about either one of those things you mentioned. I know what MAF stands for but thats about it.

Yea, get a Chilton AND a Haynes manual.

Total cost $30 and well worth it.

Go to the wrecking yard and get another MAF sensor and see if it works.

Also, unplug the MAF and see if the engine runs worse or not.