My 2011 f150 with 3.5 ecoboost check engine light came on after a couple of hard accelerations with misfires last night. I have never had a code before but have noticed some misfires form time to time under hard acceleration. The scan tool says it has code P0151 which is "oxygen sensor circuit low voltage bank 2 sensor 1". Which o2 sensor is this and how do I find it? Is there any other possible causes? Truck has 52K on it and so far has run good except for the occasional full throttle misfire.

 

Are you running a tune, if so dose it do this on stock tune?

 

Plugs? Have you drilled cac?

 

No it is all stock.

 

Original plugs and nothing drilled yet. Should I start with replacing O2 sensor? Where is bank 2 sensor 1?

Thanks

 

dmarkjohn1, I recommend you do a very systematic approach.

On new electronic controlled systems you have diagnose what caused the fault code and conditions. Based upon what you posted, you may have two separate conditions:

1. Misfire under acceleration. The trend I have seen here in this forum is the OEM Motorcraft platinum plugs do not make it anywhere near there supposed 100K service life interval. The 3.5L turbo-charge motors appear to shorten their life considerably. I have seen recommendations to change then every 50K miles. For this problem I would recommend you remove and replace the plugs with Motorcraft SP534 plugs and gap then at .030 to .032 inches.

2. code P0151 "oxygen sensor circuit low voltage bank 2 sensor 1". This appears to be A low voltage for O2 sensor heater. According to the Ford ODB II diagnostic system description in the link below, the PCM only samples the heater voltage one time per drive cycle so keep this in mind when troubleshooting.


https://www.motorcraftservice.com/vdirs/diagnostics/pdf/OBDSM1300.pdf

To determine where and which sensor, look at the info posted in the link below:
http://www.f150forumz.com/showthread.php?t=524


Good luck!

- Mike

 

That is the drivers side sensor in front of the catalytic converter. My truck threw the same code earlier in the fall. Replaced and no more code. I don't think it's coincidence this is happening on the drivers side bank because that's the side that always showed issues with plugs and coils from the moisture ingestion, and that's the side where the cats were getting knocked out from moisture ingestion.

I haven't been able to confirm 100% but I believe the cats are clogging up from this moisture ingestion causing misfires, limiting exhaust flow and causing the sensors to get plugged up, throwing this low voltage code.

 

Thanks to all who responded. Here is an update-
I replaced drivers side upstream O2 sensor and the check engine light went out. I was still getting misfire and flashing check engine light at hard acceleration. Last night I changed plugs and plug boots to the SP534 plugs gapped at .030. Also I removed the CAC and cleaned about 2 oz of brown gunk out of it. Took for test drive and now it runs like new with no problems.

My problem was likely the plugs were bad which fouled the O2 sensor. I'll be keeping an eye on things to see if any problems return but I am thankful for those on this forum who helped me get this fixed without having to take to the shop and likely saved a large repair bill!

 

I'm not familiar with the acronym "CAC", can someone explain? Thanks

 

Charge-Air-Cooled (aka intercooler)