O2 sensor trouble

[Tdean91491]

Good news is the cats definitely needed replacing, they were almost completely stopped up. Cleared the code & drove it for a while yesterday. Bad news is the code came back. Could someone point me in the direction of what wires to test at the ECM?

 

[df2x4]

Could've told you the cats weren't the issue... The O2s would have thrown a different code. No activity code is pretty much always the sensor or the wiring.

EDIT - In the interest of being helpful though, what year is the truck and what engine?

 

[Jesse_Wenting]

I've started having this issue recently. P0140 was expected as I replaced the factory 5.7 style dual cat with a 5.0 style Y pipe to single cat, so I only have one post cat O2 sensor. Not sure why I'm getting P0160 though.

Does a downstream sensor "failure" affect my fuel consumption or anything like that? IIRC I read somewhere that only upstream O2 sensor failure will put the engine into limp mode?

Edit: thought I'd throw out there that I wasn't getting any O2 sensor codes before the exhaust work. Cat was replaced simply because it was close, never used, factory style, and the price was really good. Sensors were preventative maintenance while I had everything apart

 

[RichLo]

I've started having this issue recently. P0140 was expected as I replaced the factory 5.7 style dual cat with a 5.0 style Y pipe to single cat, so I only have one post cat O2 sensor. Not sure why I'm getting P0160 though.

Does a downstream sensor "failure" affect my fuel consumption or anything like that? IIRC I read somewhere that only upstream O2 sensor failure will put the engine into limp mode?

Edit: thought I'd throw out there that I wasn't getting any O2 sensor codes before the exhaust work. Cat was replaced simply because it was close, never used, factory style, and the price was really good. Sensors were preventative maintenance while I had everything apart

You are correct that as long as there are no codes for the upstream O2s your truck will run and drive fine. But you shouldn't have codes for the downstream since you replaced them and have new cats in there. Maybe you could try cleaning out the plug connectors with some MAF sensor spray cleaner and put some di-electric grease on them.

 

[Jesse_Wenting]

You are correct that as long as there are no codes for the upstream O2s your truck will run and drive fine. But you shouldn't have codes for the downstream since you replaced them and have new cats in there. Maybe you could try cleaning out the plug connectors with some MAF sensor spray cleaner and put some di-electric grease on them.

I have a feeling it's gonna end up being some kind of wiring problem yeah. What's interesting is that P0140 is a pending code, while P0160 is an active code. Gonna do some a voltage test and probably end up making a custom O2 sensor harness. End goal is to redo all the wiring in the truck anyways so

 

[RichLo]

Thats a pretty ambitious goal. Has the truck been trouble with the wiring already? Mouse damage or flooded??

 

[Jesse_Wenting]

Thats a pretty ambitious goal. Has the truck been trouble with the wiring already? Mouse damage or flooded??

Nah, not that I know of at least. Just want that peace of mind that comes from replacing wires that are older than me lmao. Gonna stick with metripack connectors for all the factory connections, and use deutsch style for anything I add.

I'll be doing the engine/trans/transfer case harness and everything in the engine bay when I drop in the 350 I'm currently building up. Tbh after that there's not much left; I have to take the dash out to replace the heater blend doors anyways so that harness will obviously happen at the same time. A mild sound system upgrade is on the list (50w speakers, nothing crazy) so I'll do the harnesses that runs down the driver side interior and up the rear pillar then as well. Pretty sure that only leaves the harness that runs down the frame to the rear of the truck, I'll do that whenever I feel like it since it's so easy to access lol

 

[Jesse_Wenting]

Well that's just great. So the wire that runs from the 02 sensor(s) to the harness above the transmission/transfer case is fine. So I'm gonna have to chase this through the engine harness

 

[GoToGuy]

Do you have a 96 or later obd2? With obd2 you have upstream sensors for fuel trim and aft sensors to monitor cat health. Do you do anything ECM wise to overlook the sensor losses? As in bank 1, bank 2 upstream, same downstream codes?

 

[Jesse_Wenting]

Do you have a 96 or later obd2? With obd2 you have upstream sensors for fuel trim and aft sensors to monitor cat health. Do you do anything ECM wise to overlook the sensor losses? As in bank 1, bank 2 upstream, same downstream codes?

98. Not getting any problems with either upstream sensors, just with sensor 2, bank 2. P0140 is because the downstream sensor from bank 1 doesn't exist any more.

Anyone know what pins on the ECU are for the downstream O2 sensors?