Several weeks ago I had the catalytic converters changed out on my 2003 Land Rover Discovery 2. I'm located in Costa Rica and the local fix is to cut out the old ones and weld in universal replacements. After the change I was getting an SES light and my scanner said it was due to lack of signal on both front O2 sensors. I did a live test and the signal voltage on each was 0 volts and both banks were running open loop (OL). I disconnected each cable and sprayed with contact cleaner and reassembled - same test results. The mechanic didn't remove the sensors when he welded in the new cats so I figured they were damaged by the heat of the welding, and so I ordered new (Bosch) sensors from the states. Fast forward 2 weeks - suddenly my SES light went out and when I did a live scan I find that both banks are running closed loop (CL) and the voltage readings are fluctuating between normal values. Has anyone seen this before? Any ideas how this would happen? Should I go ahead and replace them anyway?

 

Nope, never seen anything like that before. Thought maybe he (mechanic) damaged the ECM by welding on vehicle without disconnecting battery. But, now that everything is working correctly, that doesn't sčem likely.

My next guess would be ground cables and terminals connecting to body. Maybe the welding caused a poor ground (corroded) connection somewhere to lose connection to battery, just enough to throw off the ECM? So, l would probably check those.

Brian.

 

Thanks Brian,

I didn't think about a ground wire. Is there a common ground wire connecting to both sensors? That might explain why both stopped working and restarted at the same time.