Ok so last year I replaced the passenger side exhaust manifold on my 1999 F150 5.4 4WD and just this past weekend I replaced the drivers side exhaust manifold as well as the EGR tube. Everything went very well for the manifold replacement.

After driving it for a few times I got a check engine light and scanned it out to get the code P1151 which is Lack of HO2S-21 Switch, Sensor Indicates Lean. So i cleared the light and it came right back that same day. I cleared the light again and it was gone for a few days so I thought I was in the clear but it came back on again....

The OBD2 Scanner that I have doesn't do live data (3100) so I took a trip down to Autozone and used theirs (Acutron 9580) *Birthday Wish list *

At Autozone I was going through the PIDs and found the voltages coming from the o2 sensors and noticed that the O2S21 (Bank 2 Sensor 1) was zero volts and once in a while would go up a tiny bit (0.020v max) but stay relatively close to 0 compared to the other 3 sensor voltages. (other sensors were at least 0.1v). I attached a picture of the Acutron with the voltages shown as the engine was running.

P1151 isn't a code specifically for an heated oxygen sensor and there are many things that can cause this code to come up such as vacuum leaks, EGR valve, leaking intake gasket and many other things but could be a bad o2 sensor. But I am thinking that I simply need to just replace the O2S21 sensor or maybe just clean the contacts on the connector?

Does this sound like I am headed in a good direction?

Thank you,
Ricky

 

The 1151 is specific to sensor 1 bank 2.
The code description tells you that. This is the difference between 1151 and 171.
Check the plugup by exercising the plug assembly.
If no hot output, replace the sensor or swap with the rear on that side.
With no output, the PCM uses a fixed fuel table in place of the sensor's output which makes that bank run on the rich side for fuel.
Good luck.