Rear O2 sensors off with stock tune

[Edqe]

Smog testing is right around the corner. Had a CEL recently for Evap. Replaced the Evap cleared the code and all was well. Several months later another CEL. Scanned for codes and all 02 sensors were triggered. 12v to all sensors. Remaining 3 wires to O2’s ohms out to ground, telling me there’s no break in the circuit. Replaced all O2 sensors, same issue. Bought a blue driver scanner, all O2 sensors seems to be reading fine. Did a complete drive cycle and passed all emissions readiness on the scan tool then shortly after O2 light comes on again. I’m like WTF! So I returned the tune to stock and noticed with stock tune it was only registering the front O2 sensors on the blue driver scan tool. Anyone can confirm if stock tune only reads the front O2 sensors? It reads all 4 when I load 93 Brenspeed tune just fine.

View attachment 93426

 

[stkjock]

did you do another full drive cycle (per the specifics in the manual) after you loaded the stock tune?

these cars have a cascade effect with the readiness on the sensors. I had the issue on my 06GT with a custom tune and needed a full drive cycle to reset all.

 

[Edqe]

did you do another full drive cycle (per the specifics in the manual) after you loaded the stock tune?

these cars have a cascade effect with the readiness on the sensors. I had the issue on my 06GT with a custom tune and needed a full drive cycle to reset all.

I’m working on that now. 60miles driven since returning to stock. Still shows not ready. You have the drive cycle steps to cover?

 

[stkjock]

I’m working on that now. 60miles driven since returning to stock. Still shows not ready. You have the drive cycle steps to cover?

I do not, but it's in the manual, if you have it, take a look, otherwise it can be found online, it's not about miles, there's a very specific sequence to follow

 

[moooosestang]

Can't see how the stock tune would have the rear 02s off since it's something you used to have to ask for in a custom tune, but i know brenspeed turns off long term fuel trims, at least with their supercharger tunes. My rear o2's have been turned off in the tune for years. Are you able to read LT and ST fuel trims?

 

[07 Boss]

Can't see how the stock tune would have the rear 02s off since it's something you used to have to ask for in a custom tune, but i know brenspeed turns off long term fuel trims, at least with their supercharger tunes. My rear o2's have been turned off in the tune for years. Are you able to read LT and ST fuel trims?

It might not be the stock tune.

 

[moooosestang]

It might not be the stock tune.

Good point. the car might have had an aftermarket tune on it when he bought it

 

[Edqe]

Good point. the car might have had an aftermarket tune on it when he bought it

Probably, I bought it used.

 

[Edqe]

Update: unsure of what adjustments were made on stock tune I went ahead and reinstalled the 91 Bren tune and did a drive cycle. Couple concerns I noticed. 1) Evap triggered a pending code, then went ready shortly after. 2) O2’s went ready, then triggers a pending code. Catalyst still not ready though, but currently have 2 pending codes that I know will soon go active and I’ll be back to square 1.

 

[Edqe]

Also, I’ve replaced the Evap canister and gas cap.

 

[moooosestang]

Also, I’ve replaced the Evap canister and gas cap.

There's a lot of crap in that evap mess that can go bad. the purge valve under the hood, pressure sensor under the trunk. I removed all mine because no inspections.

 

[Edqe]

Final Update****THE FIX!

After much thought and searching of similar issues. I decided to dig a little deeper into the Evap system. Aside from Evap purge valve located under the hood on the driver side, P0443 can also be triggered by the VAPOR CANISTER VENT SOLENOID. This little trouble prick is located under the trunk on the driver side. Ok to summarize the functions of these two parts. Evap valve dumps gas vapor into the engine. Vapor canister draws in air. While I was opening up my fuel cap I notice it was under vacuum and hissing while I was opening it. That’s where my search started and led to the Vapor Canister being the culprit.

Changing the part took no more than 15min. Did a quick KAM reset. Next I did idle relearn. Followed by a drive cycle. All emissions test went ready within 15 miles of driving! Boom! Hope this helps others experiencing the same issue with codes: P0443, P0053, P0054, P0059, P0060.