O2 Sensor
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Cruiser
Joined: Apr 2015
Posts: 186
Likes: 14
From: Lost Wages, NV
O2 Sensor
I recently moved into a new place and for the life of me, I can't seem to find my FSM so I'm coming to you guys for a little help. Bike is a 2015 Street Bob that has been popping and backfiring some. Pulled the codes and got all kinds of **** that lead back to O2 Sensors. So, I started the bike while checking sensor data on both O2 sensors. At idle, my forward O2 Sensor is reading 0.8 volts while my rear is reading 4.9 volts. Obviously, one of the sensors took a crap but without my FSM, I don't know what the actual reading should be. Anybody able to help me out a little?
Cruiser
Joined: Apr 2015
Posts: 230
Likes: 25
From: Pacific Northwest
Which codes did you pull? With AFR set at 14.6, O2 sensor voltage should be about 0.45 volts. Your rear O2 could be the culprit. But remember an O2 sensor is just that, a sensor. There could very well be another problem and the sensor is working as designed.
Last edited by dlporter; Mar 26, 2018 at 06:23 PM.
Stellar HDF Member
Joined: Feb 2016
Posts: 2,066
Likes: 259
From: Northstreet, michigan
It isn’t likely that both of them are bad but one of the ways I diagnose o2s is by taking a propane or map gas torch, and connecting a hose from the end of the torch to the air intake then turning the gas on slightly while the bike is running. Since the gas is occupying the space of air, your bike should run lean and your o2 voltage should go low. Then if it changes, remove the o2 sensor, and run the bike while slowly moving it away from the o2 bung. Now the voltage should increase.
It’s not nearly as much work as it sounds, and it’s an easy way to determine if they’re fun ruining correctly. Both o2 sensor readings should be close to the same. If you do this, and the o2s respond correctly, you’ll want to start looking at your injectors. I like to swap injectors and see if the bad o2 reading switches cylinders. Sorry for the long reply, hopefully this helps a little
Cruiser
Joined: Apr 2015
Posts: 230
Likes: 25
From: Pacific Northwest
i could be wrong, but I was under the impression they should read between .5-4.5 volts. I’m a Chrysler tech and automotive o2s read in millivolts, but all other sensors normal range is between .5v and 4.5v. Generally less than .5v and above 4.5v is when there’s an issue.
It isn’t likely that both of them are bad but one of the ways I diagnose o2s is by taking a propane or map gas torch, and connecting a hose from the end of the torch to the air intake then turning the gas on slightly while the bike is running. Since the gas is occupying the space of air, your bike should run lean and your o2 voltage should go low. Then if it changes, remove the o2 sensor, and run the bike while slowly moving it away from the o2 bung. Now the voltage should increase.
It’s not nearly as much work as it sounds, and it’s an easy way to determine if they’re fun ruining correctly. Both o2 sensor readings should be close to the same. If you do this, and the o2s respond correctly, you’ll want to start looking at your injectors. I like to swap injectors and see if the bad o2 reading switches cylinders. Sorry for the long reply, hopefully this helps a little
Stellar HDF Member
Joined: Feb 2016
Posts: 2,066
Likes: 259
From: Northstreet, michigan
The 0.45 volts number came out of the electrical and diagnostics manual. The manual makes the assumption that the AFR is set at 14.6 at idle, which I believe the stock maps probably are. The manual has a progression of troubleshooting methods to determine if there is a ground, then to check the operation of the sensor. At the end of the troubleshooting progression, assuming you rule out other mechanical issues like fuel injectors or intake leaks, harley has you either replace the O2 sensor or the ECM depending on what the sensor voltage is reading.
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Cruiser
Joined: Apr 2015
Posts: 186
Likes: 14
From: Lost Wages, NV
I don't remember what all the codes were. They all had to do with cylinders running rich or lean and one for an O2 sensor voltage. I cleared them and then started the bike while watching the sensor data. I know that it may not be the sensor at all but they are relatively inexpensive and pretty easy to change so I'll change it and if the problem persists, go from there. Thank you for taking the time to look for me.
Last edited by Andy02; Mar 27, 2018 at 10:35 AM.
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