Fuel Trim Deviation (1 Viewer)

[lehiguy]

I know just enough about the electronics of these rigs to be dangerous. Does anybody know how much positive fuel trim a 100 series will tolerate before tripping the CEL? I'm driving an '06 with 205K. My long-term trim numbers are +7.8 on one bank and +6.3 on the other. I'm getting a repeated P0420, which I know is related (and not likely the cats as the code indicates). I'm thinking I may have a vacuum leak that I can't yet find. The exhaust system is as tight as a drum.

 

[jerryb]

35-+

 

[white_lx]

P0420 will not be set based on fuel trim. It would result in a P0171/P0172. See the link below for how to diagnose a P0420.

Code setting criteria for a P0420/P0430:

After engine and catalyst are warmed up, and while vehicle is driven within set vehicle and engine speed range; Waveforms of rear HO2S alternates frequency between Rich and Lean (2 trip detection logic)

Code setting criteria for a P0171/P0172/P0174/P0175:

If the total of the short−term fuel trim value and long−term fuel trim value is within +-35 % (engine coolant temperature is more than 75C(167F)), the system is functioning normally.