2012 GLK-350 bogus bad AFR/O2 sensor (P0135 code)
Thread Starter
Newbie
Joined: Jun 2013
Posts: 5
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From: Connecticut
2015 C300, 2017 GLC
2012 GLK-350 bogus bad AFR/O2 sensor (P0135 code)
Had a front driveshaft failure at speed and it caused other damage, as tends to happen. It hit the transmission hard enough to create a hairline crack and it took out the right side upstream O2 sensor and put a couple of dents in the catalytic convertor. Took it to non-Mercedes shop who were able to replace the driveshaft and the sensor. When they returned the car it was running again but still had the P0135 code for heater circuit on the upstream O2 sensor plus P0301, P0302, P0303 misfire codes as a result of the sensor apparently not working correctly.
I patched the hairline crack in the transmission with JB-Weld, and it seems to be working just fine, dropped the transmission pan, replaced the filter, filled the transmission to spec. Transmission is fine. Also replaced the right catalytic converter since it had some "deepish" dents.
Have spent a couple of weekends trying to diagnose the sensor issue. Swapped the sensor again just in case, nothing. Swapped sensors side to side and the issue stays on the right side.
Bottom line is if you reset the codes, the car drives perfectly for 10-15 minutes or 3-5 miles and the codes come back. Once the code comes back it starts running rough again. I checked the plug that comes down from the car's computer and there is indeed voltage across the heater circuit (Middle two pins) and there is plausible voltage on other pins. As far as I can tell there is no fuse inline to the sensor- plus if it was blown there would be no voltage across the heater pins anyway, right?
So hoping the fellow forum members can point me in the right direction.Nice car, would like to get it back on the road.
Thanks,
Joe L.
I patched the hairline crack in the transmission with JB-Weld, and it seems to be working just fine, dropped the transmission pan, replaced the filter, filled the transmission to spec. Transmission is fine. Also replaced the right catalytic converter since it had some "deepish" dents.
Have spent a couple of weekends trying to diagnose the sensor issue. Swapped the sensor again just in case, nothing. Swapped sensors side to side and the issue stays on the right side.
Bottom line is if you reset the codes, the car drives perfectly for 10-15 minutes or 3-5 miles and the codes come back. Once the code comes back it starts running rough again. I checked the plug that comes down from the car's computer and there is indeed voltage across the heater circuit (Middle two pins) and there is plausible voltage on other pins. As far as I can tell there is no fuse inline to the sensor- plus if it was blown there would be no voltage across the heater pins anyway, right?
So hoping the fellow forum members can point me in the right direction.Nice car, would like to get it back on the road.
Thanks,
Joe L.
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Joined: Jul 2012
Posts: 1,369
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From: WI
GLK 250
Maybe the wiring itself is damaged? The new sensor may be just fine, but if the plug/wiring is frayed somewhere and it makes intermittent contact to throw codes, you'll have the issue persist.
Or maybe the new sensor is supposed to be "learned" to the car, called an adaptation, which requires a MB Star or Xentry diagnostic tool/system.
How many miles on your 4Matic when this happened?
Or maybe the new sensor is supposed to be "learned" to the car, called an adaptation, which requires a MB Star or Xentry diagnostic tool/system.
How many miles on your 4Matic when this happened?
Thread Starter
Newbie
Joined: Jun 2013
Posts: 5
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From: Connecticut
2015 C300, 2017 GLC
> Maybe the wiring itself is damaged?
It "looks" fine, and there are plausible voltages (Around 10-12 on the heater pins, lower on others) at the plug. This plug would be a foot or more away from where the driveshaft was flailing about and the wiring doesn't look like it was yanked or stretched.
> maybe the new sensor is supposed to be "learned" to the car,
Was hoping someone could outline the steps to *verify* that the proper voltages are available at each pin on the plug coming down from the computer. Or perhaps someone would know if the new sensor needs to be trained. FWIW not seeing any mention of that on Google searches for the specific car, or similar mintage. Hopefully a forum member would know whether or not that was a required step.
130k on the car when the u-joint gave out.
It "looks" fine, and there are plausible voltages (Around 10-12 on the heater pins, lower on others) at the plug. This plug would be a foot or more away from where the driveshaft was flailing about and the wiring doesn't look like it was yanked or stretched.
> maybe the new sensor is supposed to be "learned" to the car,
Was hoping someone could outline the steps to *verify* that the proper voltages are available at each pin on the plug coming down from the computer. Or perhaps someone would know if the new sensor needs to be trained. FWIW not seeing any mention of that on Google searches for the specific car, or similar mintage. Hopefully a forum member would know whether or not that was a required step.
130k on the car when the u-joint gave out.
