P0136 code following spacer installation at second O2 sensor to kill P0420 code

[jkhattra]

Installed an L-shaped spacer (3 x 3 inches) at the second O2 sensor on a 2000 Forester, to lay to rest the P0420 code that has been coming on weekly for the last five years! Now I'm getting a P0136 code. My understanding was that the O2 sensor distal to the cat served no critical purpose, other than to warn of poor emissions. But some P0136 code explanations suggest that the ECU may interpret P0136 as a lean fuel/air state. Is this true for a 2000 Forester? Should I shorten the spacer to avoid a P0136 call? Both original O2 sensors were replaced with new ones a couple years ago.

Edited April 23, 2017 by jkhattra

[WoodsWagon]

A single drilled out spark plug anti-fouler is enough of a spacer to fool it, and it only pulls the sensor back enough so the tip is flush with the hole in the pipe. I don't see why you'd want a 3" long spacer? You need some exhaust flow going by or the sensor will just sit in a pocket of air left from when the engine was off and always read lean.

[Fairtax4me]

Either the sensor was damaged during the work of the connector isn't plugged in all the way.

[jkhattra]

Thank you! Will shorten the spacer and doublecheck for sensor/wiring damage.

Cheers

[GeneralDisorder]

If the spacer is properly installed into the REAR O2, it cannot cause the P0136 code. The rear O2 does not affect mixture control except on '05+ models. 

 

GD