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Upstream o2 sensor harness side wire hunt

Chumpy

Member
Joined
Apr 4, 2024
Messages
7
Location
Kansas City, Missouri
Hi all. Just got my hands on 1410. Check engine light is on. When I put it on the lift to start going though the car fist thing I noticed was the upstream o2 sensor is missing its wiring. I've got an o2 sensor replacement ordered but for the life of me I can't find where on the harness the o2 connector/wiring is. Two part questions:

Can anyone make my life easier with a picture or a general description?
And I'm thinking that the o2 sensor is the cause of the check engine light. Does that sound about right?

20240407_170748.jpg
 

Chumpy

Member
Joined
Apr 4, 2024
Messages
7
Location
Kansas City, Missouri
Update: Digging around the forums I found the maintenance manual. That says that the upstream o2 sensor is plugged directly into the exhaust manifold. Makes since, and I did find what looks to be an o2 sensor up there. That brings me to the next question. What is the sensor upstream the cat in the picture above? An EGT?
 

mitsuturbo

Well-known member
Joined
Jun 2, 2008
Messages
3,551
Location
Near Seattle, Washington
There is no "upstream" or "downstream" o2 sensor. There's only one on the car, and it's not in the exhaust manifold on a stock VR4. It's in the O2 housing, which is bolted to the turbine housing with 4 bolts.
That there does not look like any o2 sensor i've ever seen.
I think VFAQ or the FSM likely have the procedure documented for checking CEL codes with an analog multimeter or a test light. Pull the code.
The o2 sensor harness/plug typically connects right under the thermostat housing and is held to the water tube that goes to the heater core with a small metal bracket.
 

Chumpy

Member
Joined
Apr 4, 2024
Messages
7
Location
Kansas City, Missouri
Thanks for the info. Looking at the manual your right it only lists a heated (I have the bad habit of calling that one the 'upstream' on any car) O2 sensor.
1712951596865.png A search though the maintenance manual also didn't show any exhaust temperature sensors. I wonder if this is an exhaust system from a different car with a 4g36t and that sensor was used to plug a hole.
I found the procedure for pulling the code. I'll see what the computer has to say.

Thanks again.
 
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