Thanks, I've been racking my brain all day to what is causing this. I don't think the sensors are at fault. Its got to be something to do with the wiring since it was fine before I cleaned them with electrical cleaner but I don't know what. I don't want to replace both sensors for the fault to stay.

the issue may not be with the one you cleaned, as unless you did the exhaust side, you may find it is just that one sensor?

I didn't remove the sensors from the exhaust just cleaned the electrical connections. So just unplugged the plug connectors and cleaned them, then refitted them. Dont know why it's now coming up with both o2 sensor faults.

could be that its not really making a good connection, best bet is to try and clean the sensor heads themselves.

Yeah might have to try that, as a Ford o2 sensor Is £199! These Ford parts aren't cheap. Wish I never touched them now, but I dont know how disconnecting a plug and plugging it back on could causes this unless its coincidence that one sensor has gone down. It's really bugging me now!

short of breaking an already bad connection theres little than can be done.

I think the broken wire probably already existed to be honest, you just brought it to light.

Yeah, maybe the sensor was on its last legs anyway and moving it around just finished it off. Think the best thing to do is try a new upstream sensor and see what happens. I can buy a NTK one for £79 so might try that.

still check things like continuity, resistance etc and see if there can be any improvement.

I've checked as much as I can and everything seems normal. My brother has a mk1 focus 1.8 and I think the o2 sensor uses the same connector. So probably going to try that on my one and see what happens.

fingers crossed it works out as a simple error!

Thanks, I hope so. Will update Wednesday when I try my brothers sensor.

I drive mk2 focus 1.8 duratec and have been experienced with pinking noise and i do a carbon clean to the engine and the pinking is gone. Hope it'll help.

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I replaced both o2 sensors and the fault codes have gone now. The electrical cleaner must have shorted out the sensors.

Knocking on uneven roads could be drop links VERY common problem :D