Hi,

New to forum, just registered today. Ran across this website by Googling.
1991 Pontiac Bonneville LE 3.8L

I'm having trouble figuring out why I am still getting these codes. I have changed the oxygen sensor on the manifold between the firewall & the engine. I believe 26 is the code for the oxygen sensor, but don't know what 12 is. Hope someone can give me a clue. Or point me in the right direction. Is there another O Sensor, that I can't find?

Thanks,

RRR

Here are some OBD1 codes relative to your post:

26 quad-driver module (computer) circuit #1 fault
12 System normal
13 oxygen sensor circuit open
44 oxygen sensor lean exhaust
45 oxygen sensor rich exhaust
63 oxygen sensor right side circuit open or map sensor out of range
64 oxygen sensor right side lean exhaust indicated
65 oxygen sensor right side rich exhaust indicated

Code 26 is related to a failure in the ECM, which is related to a device (such as a sensor) the ECM controls on circuit #1. You don't want to replace the ECM until you find out what caused the failure.

We will need someone with a 91 FSM to tell us what devices the ECM controls on circuit #1.

What operating problems are you having with your car?

Please add your year and trim of your vehicle to your signature line. That way when you start asking questions in other areas of the forum, we all have a better idea on how to assist you. Click on "Quick Links" above, go down to "User Control Panel" and then click on "Edit your Signature" It'* pretty straight forward from there.

Not really having any operating problems with the car.

The inspection sticker is expiring at the end of this month. The "Service Engine " light is on. And it won't pass inspection if that is on.

What is a 91 FSM? And something tells me a dealership is the only one that would have one.

FSM = factory service manual ... Someone in the forum will have one for a 91.

Did you check for codes, or did someone pull them for you? Do you know how to check for codes? Read this thread:
https://www.gmforum.com/t278820/

That is how I got those codes. Using a jumper wire and reading the flashes.

Thank you.

I will post a request on the forum for the manual.

Not necessary. This thread will alert people to what we are looking for, and if we don't get a response I will send PM'* to a few people.

Does someone have a '91 FSM to help us to understand what a failure on circuit #1 on the ECM could be related to?

Circuits on QUAD #1 are they canister purge sol per Alldata
pin YC3 Dark Green with Yellow tracer.
and YC11 Brown with a White tracer. I would try unplugging the purge sol and see what happens.

I forgot Pin YC2 Dark Green With an Orange tracer. It is for the low speed fan relay.

New to the forum. Sorry about that.

I posted a new thread requesting FSM. Should have kept it all together...so it could be followed easier.

Should the battery be disconnected before I pull anything?