2000 Alero 3.4 Heat Circuit Sensor 1 Bank 1

My SES light just came on and the code came up as a malfunction with the heat circuit in Sensor 1 Bank 1. Any and all info would be appreciated. Specific answers I'm looking for are, whereabouts is sensor 1, bank 1. Has anyone else had this issue? If so, did repairing the sensor fix it? Not that it matters as much but, are there any specific pitfalls to lookout for, special tools necessary?

As always...Thanks for your input!

It would help to post the specific code. P0135?

The bank 1, sensor 1 02 sensor (pre-CAT converter) is located on the exhaust system, rear bank exhaust manifold where the downpipe connects.

You can check the 12 volts and ground at the 02 sensor electrical connector used for the heater element. If that is good then most likely the 02 sensor.

To remove all you need is a universal 7/8" 02 sensor removal socket/tool.

Thanks for the quick reply. Yes it is P0135. Do you recommend using a GM O2 sensor if that is the problem, or will an a/m one suffice in this application?

On the 02 sensor I would stick with the AC Delco, part number AFS109.

Some members used aftermarket brands like Bosch and the results were mixed. Some premature failures and biggest complaint was fuel economy was down using that brand.

I'll stick with the AC Delco then. I'll be sure and post results.

Thank you sir, your advice on this forum has helped me more often than you know.

I replaced the O2 sensor with a Bosch Universal unit. I reset the SES light, and within two hours, it's back on throwing the same P0135 code. I reset it again. Same thing happens. P0135 sensor 1 bank 1. Where do I go from here?

Bosch universal 02 sensor?

The next step would be to check the heater circuit input voltages to the sensor at the electrical connector and if that is good 02 sensor activity at the output.

When testing the inputs and outputs, how many of the four wires should have power? I had previously tested the two black wires on the input plug. Only one had power coming from it. I tested from the female connectors on the inside of the plug. Once I establish whether the correct power is getting to the the output plug, what am I looking for to happen on the other end? I mean, which wires will be powered up at that point on the output side?

When testing the inputs and outputs, how many of the four wires should have power? I had previously tested the two black wires on the input plug. Only one had power coming from it. I tested from the female connectors on the inside of the plug. Once I establish whether the correct power is getting to the the output plug, what am I looking for to happen on the other end? I mean, which wires will be powered up at that point on the output side?

You know a crazy thing happened. The SES light went out today. Will it stay out? Who knows? I'd still like to know the electrical testing procedure. Thanks.

I've got a wiring diagram showing the heated oxygen sensors, I'll be glad to email it to you if you PM me an email address. It looks like the brown wire should have 12 volts when the key is in run. Also, check the ERLS 10 amp fuse in the underhood fuse block, that is where the brown wire gets it's power.

New issue to throw on the fire. I pulled up a P0131 "Low Voltage" code. The P0135 still exists as well. Any thoughts?

So I decided to get the factory ACDelco O2 sensor. Disconnected the battery, installed the new O2 sensor, let the car sit for an hour, connected the battery before I started it I plugged in the scan tool and without touching a button it read "Pass, no codes." Ordinarily it would immediately tell me if there were an issue. I then started the car and immediately noticed a difference. First the SES light was off then the idle was back to normal. So I'll keep my fingers crossed and cycle the ignition a few more times before taking her in to smog, but so far so good...

To put an end to this saga...I wanted to let whoever is interested know that my car passed the CA. Smog test with no problem!

Hi- I have a 2000 Alero 3.4 with the same problem.

P0131 O2 sensor circuit low volts (bank 1 sensor 1).

Any chance you have the part number or anything for the AC Delco O2 sensor? Was it before or after the cat converter? I really appreciate the help.

Thanks again-

Nick

Hi Nick,
I'm sorry I don't have the part # but I will tell you that I purchsed it from the dealer, because I wanted the ACDelco unit. I tried a Bosch one from a local parts store, and it didn't work. So in the long run it actually cost me more.
The one I had to replace was before the cat, located on the rear exhaust manifold (the one closest to the firewall). Pretty easy to remove, even without an O2 sensor socket.