Hi, I've got the following error codes coming up on a Ford Focus 2005 Mk2 1.6Ti VCT:

P0036 - HO2S Heater Control Circuit (Bank 1 Sensor 2)
P0056 - HO2S Heater Control Circuit (Bank 2 Sensor 2)

P0136 - Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
P0156 - O2 Sensor Circuit Malfunction (Bank 2 Sensor 2)
 

Running Torque I looked at the sensor voltages (see attached screenshot) with the engine at idle. B1S2 is top right, B2S2 is bottom right. Both appear to be reading about 0.35V and this appears to be reasonably steady whether the engine is just idling or revved at 2500rpm for a few minutes.

I presume this means I need to replace the two O2 sensors after the cat but it seems a little strange to me that they seem to have both gone together so wondered if there's anything else I should be checking first? I inherited the car from my girlfriend's brother for £100 rather than him scrapping it and although it doesn't seem to have anything major wrong it wasn't very well looked after so I don't really want to end up spending £80-100 on a pair of O2 sensors if there's something simple I might have overlooked.

Any help and advice appreciated. Particularly whether anyone has got any opinion on whether to get cheapie OEM sensor replacements for £20-30 each or whether I'd be better paying double the price for branded.

heater side of one of your sensors has probably broke and gone short circuit blowing the fuse that supplies both heater circuits of the sensors. 

17 hours ago, iantt said:

heater side of one of your sensors has probably broke and gone short circuit blowing the fuse that supplies both heater circuits of the sensors. 

Thanks for the quick reply. I'd already done a quick visual check on the fuses for the O2 sensors and they looked OK. Just continuity checked with a multimeter and the fuses are fine. Just been reading up and consensus seems to be that cheap eBay sensors are probably not worth the saved money so I guess I'll have a look for a couple of branded ones :/

Did you get this sorted? I have a p0156 fault. Think the rear O2 sensor I had fitted probs caused it?