Hi Guys,
My 1125r has developed a fault.
After starting up and just after the cold light goes out (2/3 mins), the engine light comes on, and stays on, with the following...
REAR 02 SYS ERR
This message goes off after 3 secs and returns to GEAR etc;
The bike runs, but can suddenly cut off without warning?? usually at low revs...

Any ideas?

Thanks in advance

If the wires on the O2 sensors are the same length swap the front and rear sensors over and see if the fault swaps to the front ............... if it does it confirms the sensor is toast.

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2001 X1 2009 1125CR 2006 Uly X3 2010 Uly a fully Maz'd S1 and a 1991 RS1200 Westwind.

Sorry for being a bit green! but does this mean oxygen sensor in the air intakes?

No ........it's the sensors in the exhaust headers.

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2001 X1 2009 1125CR 2006 Uly X3 2010 Uly a fully Maz'd S1 and a 1991 RS1200 Westwind.

OK, I have managed to remove the rear sensor, I was unable to try to swap the wires without a major strip down,
I have measured the resistance across the terminal to it's earth using an ohmmeter, and I get zero readings even at a 1000 ohm's.
I reckon this is a duff sensor, what do you think anyone?

The sensor doesn't work like that, it is essentially a fuel cell, it contains a catalyst that helps any unburned hydrocarbons turn themselves into CO2 and H2O and in doing so create a Voltage output.

You get just under 1V when you run richer than stoichimetric, and 0V when you run leaner than stoihiometric.

Bottom line is that a resistance test is not going to show if it works.

I think you are looking at a harness or connector fault rather than a sensor fault. Sensors do fail, but chaffed wires and corroded contacts are more common.

I would check resistance from the O2 sensor connector to the ECM plug as a starter. I would also check the state of the connectors and the harness. If that didn't show anything I would swap the sensor out (borrowing one if I could).

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08 Specialized Langster

OK thanks Proff!!
Will do a more detailed check/test of the wiring harness, and will report back.....

PS may take a couple of days, as loads of other menial home tasks to do!!

OK, I have tested wiring from the rear 02 connector to the ECM and I am getting a full loop,
so I can discount any fault in the wiring harness, without having a spare sensor, I may bite the bullet and buy one, have looked on ebay, and notice one is going for £38!

I will have a look to see if I have one I can lend you to try. PM me your address.

PS. Did you check for a short to ground?

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08 Specialized Langster

Drat! I did not check for the possibility of a ground fault, will report back shortly.....

Right, I've double checked wiring, full loop and no sign of a ground leakage...

Maybe you can swap the signal wires on the ECM connector to perform the test which Kevmean told you. With a little luck the wires are close together on the same ECM connector.

Have considered this, however the time it would take to dismantle the harness, disconect the leads, reverse them, then having to put them all back again, and sods law, you can never get it back to it's original state, and knowing there was nothing wrong with the wiring in the first place!!

swap the 02 sensors totally ie put the front one in the rear header and the rear in the front header ..... if the problem goes to the front then you know the fault is the sensor ............ if it keeps showing the rear then you know it's some other fault

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2001 X1 2009 1125CR 2006 Uly X3 2010 Uly a fully Maz'd S1 and a 1991 RS1200 Westwind.

It seems easier to me to go for a ride and log some runtime data, which will most probably show what seems to be the trouble ...

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"It is often said that before you die your life passes before your eyes. It is in fact true. It's called living."
Terry Pratchett