1996 850 Bad o2 Ground?

TBrown00 · Post by **TBrown00** » 20 Jan 2015, 02:11

While playing around with my new scanner and its live data mode, I noticed that it was only showing one o2 sensor (B1 S1). It wasn't even recognizing S2 and no CEL codes have been generated.

I disconnected the rear o2 sensor's wiring harness and, using my multimeter, found that the car is supplying 12V to it. I used a grounding point in the engine bay for this test. I then tested the ground wire on the harness (black probe on harness ground and red on B+ terminal) and found the ground was bad. I also tested the resistance on the o2 sensor's heater circuit and it came back normal (~3.8ohms).

Looking at the 850 manual on this site and the engine performance wiring diagram, it appears that the front o2 sensor is grounded off of the fuel injectors. I can't seem to find anything about the rear o2 sensor though. Does anyone know if both sensors are grounded with the injectors? If not, where does the rear sensor's ground go?

Also, am I on the right track here or am I totally off base?

I won't have time to get back to this until Wednesday when I'll be able to trace the wires and hopefully solve this issue.

Post by **Ozark Lee** » 20 Jan 2015, 08:11

It might be more of a scanner issue than a real problem. The lack of a signal from the rear sensor will post an error code and light the CEL.

...Lee

Post by **tryingbe** » 20 Jan 2015, 09:47

I thought the oxygen sensor is 4 wires.

1. signal
2. signal ground
3. heater 12v
4. heater ground

There shouldn't be an additional 12v other the heater.

TBrown00 · Post by **TBrown00** » 20 Jan 2015, 13:29

Ozark Lee wrote:It might be more of a scanner issue than a real problem. The lack of a signal from the rear sensor will post an error code and light the CEL.

...Lee

Interesting. Ya I was surprised there wasn't a code if it wasn't sending a signal. It's an Autel AL619. It shows all sensors on a Lexus and a Chevy at my house. I don't remeber if both showed on my brother's 95 850.

tryingbe wrote:I thought the oxygen sensor is 4 wires.

1. signal
2. signal ground
3. heater 12v
4. heater ground

There shouldn't be an additional 12v other the heater.

Yes, there's 4. I used the heater 12v and ground for my testing.

TBrown00 · Post by **TBrown00** » 20 Jan 2015, 13:49

Also, one thing I should mention. The reason I was looking into this: the scanner is showing the fuel system in a closed loop-fault when warmed up.