Need A Little Trouble Shooting Help Please

[Wingnutt]

The truck: 1999 Silverado 1500. 5.3 auto, 4wd

 

The problem: Bank 2 lean code

 

The issue: O2 Sensor test shows all sensors OK However…..

Live data scan on scanner is showing bank 2 sensors very lazy.

Readings from .14mv to .28mv

 

Bank 1 sensors reading: .08mv to .84mv

 

 

Even though the O2 test is showing all sensors OK I am still getting a lean code. I cleared the code and then drove the truck 40 miles without the CEL coming on. I stopped in at a store and shut the truck off. When I left the CEL came back on before I was out of the lot. I have checked for vacuum leaks and can’t find anything and a laser thermometer on different areas of the engine confirms the 195 degree reading that the scan tools shows. So with all that out of the way, other than replacing the lazy O2 sensors, does anybody have any other suggestions? TIA!

[Draenor]

Swap sensors, see if the condition occurs on the other bank. An exhaust leak can also cause a lean code.

[Wingnutt]

Thanks, I didn't even think about an exhaust leak. I saw evidence last night of a leak at the flange where the "Y" pipe connects to the pipe leading to the muffler (downstream of the O2 sensors). I'll throw a gasket on it tonight and see what happens.

[Wingnutt]

SOLVED!

 

What looked like an exhaust leak was a very tiny one, but there is no gasket on that joint. It's like a ball and socket joint. When I purchased the O2 sensors, I also bought a can of Sea Foam and put in the tank. I had gone less than a 1/2 mile when I noticed that the CEL had gone out! Then I remembered that a malfunctioning gas cap vent can cause either a lean or rich code. I turned around, returned the O2 sensors and went to the local dealer and bought a new gas cap. The CEL has not lit up since.