Ok so i have a re occurring sms light and my scanner says its the 02 sensor 1.... i put new brand new oem equivalent bosch 02 sensors in both the number one and two positions.... cleared codes..... after driving about 30 miles the next day when i started the car the sms came back on.... i bought a diagnostic scanner and the code sure as **** read o2 sensor 1 fault..... when i check the "running live data" i notice sensor 2 voltage is pretty steady at .785 plus or minus a bit.... but sensor 1 is fluctuating from .045 to .800 and mostly at .045 and only occasionally above that.... jumping usually from .045 straight to .800 then returning to .o45...... this is true even after i clear the fault and if i run a new check of course it says no fault listed.... because it hasnt gone through a drive cycle yet i gather.... is it normal for the number 1 sensor to be like that and the number 2 be pretty steady? Its definitely running rich the exhaust pipes are black as soot...

 

i have never had any luck with bosch o2 sensors

scott

 

ok i will give you that , however just to point out i had the fault before changing to the bosch and yet the symptoms remain the same.... i will however buy the NTK oem sensor made by NGK.... actually i already ordered them.... but to further explain.... both sensors run about .800v or bit higher at idle or steady throttle.... or even when pushing down on the throttle.... but when i let off the gas , the first 02 sensor drops volts way down to .04 or less if only for a couple of seconds while the second sensor stays pretty consistent maybe from .750 to .800 Its always at idle when the actual fault code trips after tapping the gas and returning to idle... at the same time the voltage suddenly drops.... i assume due to a sudden lean out in the pipe.... here is the info captured at time of fault on my actron OB ll:

Eng Rpm = 772
Calc. Load = 36.9
Map Hg = 14.6
Coolant Temp = 167
IAT = 135
IGN ADV = 4.5
ST FTRM 1 = 2.3
LT FTRM 1 = 6.3
02 sens s11 = .045
02 sens s12 = .785
Veh Speed = 0
Fuel Sys 1 = Closed

could this be an exhaust leak since it only goes dead lean (extremely low voltage) on sensor 1 when i let off the gas.... followed by considerable crackling and odor from the exhaust. But overall sensor two reads rich?

 

i don't have access to mini maintenance manuals, but i do for my 1997 sonoma

on the sonoma, both o2 sensors are supposed to be about .45 volt if all is well and running at constant speed, the one before the cat cycling between .8v (rich) and .1v (lean) as the fuel injection computer varies the mixture with varying load, but should definitly go to .1 volt or less when the throttle is shut as the computer turns the injectors completely off under a coasting no throttle condition, the after cat o2 sensor should remain close to .45V all the time

i believe the mini does the same, turns off the injectors when coasting (the instant mpg goes to 99.9 in the tach display while coasting)

if o2 sensor s12 is the after cat sensor, it is reading very rich and you may have a cat problem as it should be about .45 volt

other mini experts probably know a lot more than i do, hopefully someone will chime in

scott