Hello all. This is my first post. I recently purchased a 1998 Subaru Legacy Gt. I recently replaced the head gaskets, timing components, etc.. Anyways.. The car fires up and runs, however, it idles a little low and the motor has some hesitation. I recently read the code and it was for bank 1 sensor 2. When I took sensor out I went ahead and bench tested it and it was producing voltage just fine.I also checked the wiring harness and it was fine. Now my question is, what would cause the downstream 02 sensor to trigger a check engine light. Is there an exhaust leak between the two cat converters?

What is the code? There are a half dozen different codes for the O2 sensors.

 

The rear sensor won't cause any hesitation or low idle. That is usually a vacuum leak or if it has a MAF sensor could be a dirty MAF or an air leak into the intake tube between the MAF and the throttle body.

Also check the vacuum hose on the fuel pressure regulator for fuel.

p0141. there is a bit of a humming sound coming from the the MAF sensor area. I tested both of the o2 sensors and connectors with a multimeter. They both produce voltage when heated up. I did spray some MAF cleaner in the sensor. Must be air leaking that I might be hearing.

Edited December 20, 20169 yr by subarusubarusubaru

Apparently I just can't read today...

 

Anyway

P0141 is a code for the heater element in the sensor. The heater element has probably burned out. Replace the sensor and should be fine. But as I said before, that won't cause your rough idle.

 

If that car has the big air box on top of the engine make sure the bottom section of the box is clamped together properly. Also make sure the gasket that runs around it is in place and isn't dirty or split anywhere.

So the wiring harness to the o2 sensor wasn't seated properly, hence the code. The rough idle was coming from an air leak right where the intake manifold meets with the cylinder head. I found it by spraying carb cleaner around until I found the leak. I was careful to spray little amounts while the engine was cold to prevent a fire from starting. After replacing the intake/exhaust gaskets, she is running great and up for sale finally!! :D