I am having a problem with a check engine light fault code p1151, lack of upstream heated o2 sensor switch, sensor idicates lean, bank 2. At first I thought it was a bad o2 sensor and replaced it out. Now I am finding that not the case. The sensor seems to be getting little signal(from my airfuel gauge which could indicate lean or something else wrong). The truck idles rough but runs ok once I get going. What could be wrong?

 

Have you replaced an air filter or installed an FIPK as of late ?
The reason I ask is if you replace your air filter, when putting back together the intake, the PCV hose can fall off of the intake, which causes un-mettered air into the engine, and can through off the idle on the truck, or the other hose by the T/B or maybe the MAFS is not sealed correctly or the Intake Air Temp sensor is not seated well, and any of these let in un-metered air.

Another is is you have a filter similar to a K&N filter and just cleaned it, and maybe over oiled it and the MAFS is dirty from the oil ?

If you look at the PCV hose, where the 90 leaves the back of the throttle body, are there cracks in there ? This can be common to have happen on older trucks ( don't know your year ).

Have you isntalled an xhst system as of late. Leaks near the O2 sensors can cause codes to be set. Maybe a weld that was marginal let loose ??? Or the harness ( truck side of plug ) got trashed by the O2 sensor from it being up against a new system ??

Maybe a vac hose leak ?? On older trucks the vac lines have a tendancy to crack and cause problems, and this can cause problems. These are usually right by the battery box for some reason, but it could be anywhere.

All of these are swag, and questions right now thought I would get you going in the correct directions by asking some questions.

below are the sections from the manual, so you know where I am getting some of this from, if you do not have a manual handy.

Let us know what is going on, and some back ground info and we'll see about getting you on your way. We're open 24/7

DTC
P1151 - Lack of HO2S -21 Switch, Sensor Indicates Lean
Description
A HEGO sensor indicating lean at the end of a test is trying to correct foran over-rich condition. The test fails when fuel control system no longer detects switching for a calibrated amount of time.
Possible Causes
See Possible Causes for DTC P1130

DTC
P1130 - Lack of HO2S -11 Switch, Fuel Trim at Limit
Description
The HEGO Sensor is monitored for switching. The test fails when the HO2S fails to switch due to circuit or fuel at or exceeding a calibrated limit.
Possible Causes
Electrical:
- Short to VPWR in harness or HO2S
- Water in harness connector.
- Open/Shorted HO2S circuit
- Corrosion or poor mating terminals and wiring
- Damaged HO2S
- Damaged PCM
Fuel System:
- Excessive fuel pressure
- Leaking /contaminated fuel injectors
- Leaking fuel pressure regulator
- Low fuel pressure or running out of fuel
- Vapor recovery system
Induction System:
- Air leaks after the MAF
- Vacuum Leaks
- PCV system
- Improperly seated engine oil dipstick
EGR System:
- Leaking gasket
- Stuck EGR valve
- Leaking diaphragm or EVR
Base Engine:
- Oil overfill
- Cam timing
- Cylinder compression
- Exhaust leaks
- before or near the HO2S(s)