Aftermarket Exhaust Incompatability With O2 Sensors?

[chewie303]

After getting an aftermarket exhaust (old one snapped) I consistantly get the check engine light and code P0125 (Insufficient coolant temperature for closed loop fuel control) after clearing the ECU. Took it back to the exhaust place (again! see below...) and they replaced my coolant temperature sensor, no effect. Took it to Toyota and they checked all the sensors resistance and they all look fine, their best diagnosis/guess was that the welded section of exhaust where the O2 sensors are screwed in is too thick so the sensor is not penetrating into the gases getting a good reading, and cos its aftermarket they cant help me any further except getting a toyota exhaust (£700!). So, if you want something done, do it yourself....

Bought my own scanning tool and one O2 sensor never seems to read a voltage above 0.060 volts, never mind 0.450! The other one seems to be ok, flipping between low and high voltages. It seems to me that if I somehow got a longer sensor it might penetrate further into the exhaust gases getting a better reading? Easier than shaving a bit off the wall of the exhaust ;) The car drives fine, getting maybe 5mpg less than before, presumably as its not getting into closed loop fuel control mode.

Would be grateful for any help or advice.

PS. Its a Yaris 1.0 2003 (Colour Collection)

PPS. I have had a dreadful experience with the exhaust people who shall remain nameless, they made a dogs dinner of a simple exhaust replacement 3 times and I have completely lost faith in their technical ability (but thats a different story and I shall deal with them soon), therfore I want to sort this out myself if poss cos they aint touching my wee car again!

[chewie303]

The voltage from the first lambda sensor (average 0.030 volts) is ridiculously low, doing a bit more research but different sources say different thing about what this means. The Haynes manual says this indicates very rich, but almost everywhere else on t'internet says this indicates very lean, anyone know for sure which it is?