O2 sensor help (94 k3500)

[chris032188]

Does anyone have wire diagram for O2 sensor for this truck? I tried searching but finding conflicting information if it's a 1 or 3 wire. Just picked up truck and there's no o2 sensor in and i can't find the wiring so I'm unsure. Forgot to add 5.7 4x4 manual transmission

 

[movietvet]

RA says it is a 3 wire sensor. https://www.rockauto.com/en/moreinfo.php?pk=991564&cc=1053324&pt=5132&jsn=965

RA also offers a 1 wire sensor. https://www.rockauto.com/en/moreinfo.php?pk=1323881&cc=1053324&pt=5132&jsn=961

Can't find wiring? No pigtail hanging there and cannot find it cut off at the harness?

 

[chris032188]

Truck was finger f'ed heavily. I'm sure it's there just don't know what I'm exactly looking for.

 

[movietvet]

Well, it is either a 3 wire or 1 wire connector or cut harness. Good luck.

 

[someotherguy]

If you check the factory service manuals (available here free to download, check the sticky'd posts at the top of this section) - there are wiring diagrams for each possible drivetrain combination in each year.

While heated (3 wire) O2 sensors were first seen on these trucks in 1994, and I've had them with the 3 wire.. I am fairly sure your manual transmission model had the non-heated (1 wire) O2. You should confirm with the factory service manual, though.

Richard

 

[Road Trip]

Does anyone have wire diagram for O2 sensor for this truck? I tried searching but finding conflicting information if it's a 1 or 3 wire. Just picked up truck and there's no o2 sensor in and i can't find the wiring so I'm unsure. Forgot to add 5.7 4x4 manual transmission

Greetings chris032188,

The 5.7/manual trans is a good starting point, but the model year of your vehicle can be a big clue of how
it came off the assembly line. The early GMT400s were using the single wire (unheated) O2 sensors,
but GM upgraded to the 3-wire (heated) O2 sensors when the emissions were tightened and they
needed to clean up the engines during the 'warm up' period.

Please reply back with this info, and this will help us help you.

EDIT: I missed the info I was looking for in the title. My bad. D'oh!

BTW, Welcome to the GMT400 forum. And don't be bashful, pics
of your ride is the currency of this forum. Doesn't have to be a
immaculate trailer queen, we appreciate them all -- especially the ones
still earning their keep on the road. :0)

 

[chris032188]

If you check the factory service manuals (available here free to download, check the sticky'd posts at the top of this section) - there are wiring diagrams for each possible drivetrain combination in each year.

While heated (3 wire) O2 sensors were first seen on these trucks in 1994, and I've had them with the 3 wire.. I am fairly sure your manual transmission model had the non-heated (1 wire) O2. You should confirm with the factory service manual, though.

Richard

It's a 94. Is the 1 wire black?

 

[Road Trip]

It's a 94. Is the 1 wire black?

Here you go. Taken from the '94 "Driveability, Emissions, Electrical Diagnosis Manual".
(Which I downloaded from the the links in this thread: '88+ GMT400 FSMs)

You must be registered for see images attach

When trying to identify individual wires, it helps to clean those wires carefully
and use plenty of light when viewing. NOTE: Sometimes it helps to view the
insulation color up at the PCM pin for a visual clue of the shade to look for if
the wires underneath are discolored from oil leaks, heat, etc.

Hope this helps. Definitely arm yourself with all the '94 manuals from the link
above in order to give yourself an unfair advantage getting your GMT400 back
to 100% functionality.

Cheers --

 

[chris032188]

Thanks ! I actually downloaded them yesterday. Saved this wide girl from going to the scrap yard. Was a work truck it's whole life, I can tell most of the work done on it was by people other then mechanics. Trying to un f' what everyone half assed. Knock sensor wasn't connected, coolant sensor wasn't connected. Currently battling a hard start / rough idle when warm. Replaced both temp sensors (redoing tho because I made mistake of using Teflon tape on the threads), replaced the IAC. Now trying to figure out the O2 sensor situation so I can get that sorted and better start to rule things out.

You must be registered for see images attach

 

[chris032188]

Here you go. Taken from the '94 "Driveability, Emissions, Electrical Diagnosis Manual".
(Which I downloaded from the the links in this thread: '88+ GMT400 FSMs)

You must be registered for see images attach

When trying to identify individual wires, it helps to clean those wires carefully
and use plenty of light when viewing. NOTE: Sometimes it helps to view the
insulation color up at the PCM pin for a visual clue of the shade to look for if
the wires underneath are discolored from oil leaks, heat, etc.

Hope this helps. Definitely arm yourself with all the '94 manuals from the link
above in order to give yourself an unfair advantage getting your GMT400 back
to 100% functionality.

Cheers --

I seen the diagram also you posted, but I was still confused on which is should be. I'm thinking single wire since it's a dually full size?