Just put a new exhaust on my 01 5.9 and started to run rich. Replaced o2 sensors because I thought they were bad but didn’t help. Has been throwing high voltage and heater circuit codes for the o2 sensors. Any ideas? Are these two connected?

 

Could be if the heater voltage bleeds onto the sensor signal wires. Did you get the DTCs before changing the O2 sensors ? Federal or California emissions ?

 

yea the codes were thrown before. That’s why I thought the sensors were bad. Also it’s federal emissions

 

Did you clear the codes after installing them?

 

Yes I did. Came back on the next day

 

More questions : The problems started after putting the exhaust on ? What kind of exhaust, catback or everything including cat ? Or in other words, did you touch the O2 sensors ?

IIRC federal has one O2 before the cat and one after, and no mini-cat in the downpipes. There is a chance to reverse the O2 connections, so the PCM reads the after cat O2 as before cat and vice versa. That causes the PCM to read lean and add fuel. Could also be that one of the connections is just bad and it runs default tables.

 

I did a custom exhaust with high flow cats. It is now a true dual system. Yes I had to touch the o2 sensors and I do have a bung welded before and after one of the cats

 

In that case have a really close look at all the wiring. There are four wires in the O2 connectors. From the harness side: dark green/white is 12V for the heaters, brown/white is the heater control from the PCM, black/light blue is the sensor ground (common between both sensors). Tan/white is the upstream sensor, orange/black is the downstream sensor.

 

So are you thinking that I somehow switched the o2 sensors? Because that could make a lot of sense

 

I am pretty sure they are keyed so you can't switch them