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O2 Sensor Replacement Question


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Anyone ever had their's replaced on their KRS? I've been told that I may need one to correct a throttle problem. So I'm just wondering what the problems were with your bike prior to installing a new one.

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As far as I know (not sure), a bad O2 sensor causes the engine to run in 'open loop' mode, which is like if you were at sea level (just like a carbureted bike). The higher you live, the richer the mixture would get, causing sluggishness and excessive fuel consumption. And more importantly, that'd fry your catalytic converter pretty quickly.

Emissions related hardware are warranted for 100K miles on cars; I'd ask your dealer (or check your warranty manuals) about your bike, since I understand BMWs comply with 2008 standards, and might not be forced to cover these components. Please let us know; it affects all of us.


Finally, don't you have one of your idiot lights lit up? I'd assume the ECU throws a code when a sensor fails. I'm assuming here you have your bike properly tuned-up; it not, I'd start there.

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A bad O2 sensor will, indeed, cause the ECU to go "open loop". However, that has no bearing on the altitude correction, which is handled by the barometric pressure sensor built into the circuit board of the ECU. What you won't get is the slight mixture correction, actually a hunting from rich to lean, at low throttle openings and RPM. It is actually the cause of surging on the boxer motors. Your bike will run fine without it as its sole function is to keep the catalytic converter in a happy range. In fact, removing the cat code plug and disconnecting the O2 sensor will give you a European motorcycle, so long as you remove the cat as well. They have some pretty impressive mountains over there, and don't run rich at elevation.

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Paul Mihalka


We are talking K1200RS. All these bikes worldwide have the cat and oxygen sensor. I don't know how it will do open loop with a o-sensor defect code, but I guess the altitud adjustment will keep on working.

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Calvin  (no socks)

I work on cars and the technology is the same... The 02 can in fact cause a stumble when accelerating. Easy to prove the diagnosis, change it out, stumble gone, fixed...Well... maybe, what was the root cause of the failed 02 sensor...Contamination? Fuel or Coolant? Or just a bad sensor? A repeat will require further invesitgation. eek.gif

Who is the diagnostician?

Test with voltmeter while in operation at temperature. It should fluctuate between 0.2 and 0.8 volt.

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My bad,


In that case, you need the O2 sensor to protect the cat. Too rich and you will hurt it, too lean and it won't stay lit and will wind up clogged. Its not quite the same issue and the altitude correction will still work. I'm pretty sure you could still remove it and the cat and the bike will run fine. I'm not so sure about which cat code jumper would be needed, if any.

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OK Guys, Here's the situation.

98 KRS with 18,000 miles. While deacelerating or holding the throttle at a constant RPM the bike seems to hunt causing the bike to buck. This is can happen while deacelerating into a turn and then rolling the throttle back on in the turn while going downhill. It also happens while I'm in traffic at slower speeds.

This isn't just engine braking as far as I can tell. A few techs think it's the sensor or the ECU. I can pick up an O2 Sensor for half the price that BMW charges but if it's a ECM that's almost a $1,000.00 uninstalled. frown.gif


O2 Sensor

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Dennis Andress



I feel that a bad ECU would be intermitent or just plain inop. A lean, or rich, condition like you're describing would have to be a sensor of some kind. It's an electronicaly controlled engine, there's only so much you can do to it.


Try this:

  • Fix all vacuum leaks. On a `98 that means making sure the joints where the intake stubs seal against the head aren't sucking air.
  • Clean all the electrical connectors with contact cleaner.
  • Disconect the battery for 10 or 15 minutes. On Vics' site they say to turn power on and cycle the throttle full open three times after reconncting the battery.
  • Change the plugs.
  • Replace the O2 sensor.
  • Then think about changing the water and air temp sensors and the TPS, all of which made a big difference in my 91.

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My '99 KRS used to do that every so often. My take was a bad HES or wiring. If its constant, I'd be thinking ignition. Maybe a coil?


Does it only happen during the transition from trailing throttle into acceleration? Never mind, I just re-read your post.


That is surge you are describing and your tech is probably correct. It is either the O2 sensor or the ECU. That Beemer Boneyard guy has good prices on O2 sensors. I'd pick one up.


A really careful inspection of the wiring to/from the sensor might be in order as well. Lots of folks unscrew these things without removing the tank and unplugging first. They wind up damaging the wiring harness. An hour or so to raise the tank, it doesn't actually have to come off, unplug the sensor and remove it to inspect the wiring with a buzz box might provide a cheap solution.

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  • 2 weeks later...

The O2 Sensor was in fact bad, so the problem has been solved with installing a new one along with a new set of plugs.

Thanks everybody.


P.S. When Brown's BMW had the bike hooked up to their testing computer, the O2 Sensor tested OK. It wasn't until the tech tested each sensor at it's connector that it was discovered to be bad.

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