I'm diagnosing an O2 sensor fault code as mentioned in another thread. Car is a 1991 190e 2.6L with a factory installed manual transmission (717.432)

I've found a couple thorough test procedures online and have begun testing with my multimeter...But before going too far I wanted to think of any obvious causes to the problem and something came to mind.

I got the check engine light and fault-code for the o2 sensor after doing some repairs to the car. While replacing the flex discs and support bearing I pulled the entire exhaust out (leaving the manifolds attached at the head). Catalytic converter was rusted out so I cut it out and replaced it with straight pipes from the downpipe to the muffler. I also installed a new o2 sensor.

I'm assuming the o2 sensor grounds to the exhaust, and I'm now wondering if its possible I disrupted the ground. I did not notice a ground strap as I was uninstalling the exhaust.

Could I have shorted the ground to the O2 sensor? I'm assuming the ground is completed simply via the block-to-manifold-to-downpipe connection. All three are securely connected, but I'll be putting the car up on stands again to inspect.

Any input would be greatly appreciated. I'll update this thread as I conduct the tests and solve the issue, so it's useful for future visitors.


Thanks!
Roland