Snap-On code scanner save code?

[Lsxtrucker]

So I was having a random multiple misfire in my '03 silverado the other day so I took my truck to my mechanic friend. He scanned it and said I needed a 02 sensor according to the scan.

So I bought 2 new delco sensors but he didn't give me the code, and I'm unsure whether I need to replace the upstream or downstream sensors.

Will his Snap-On code scan tool save the code he found so I can call him and find out what it was even after he cleared it in my truck? I'm just trying to figure out which set to replace. 

Thanks

[davester]

It'll be the upstream O2 sensors (the ones between the engine and the cat's).  They are the only ones that are used by the ECM to control how much fuel to inject in normal operation.

 

The downstream O2 sensors (after the cat's) are only used to determine if the cat's are still functioning properly.

[Lsxtrucker]

27 minutes ago, davester said:

It'll be the upstream O2 sensors (the ones between the engine and the cat's).  They are the only ones that are used by the ECM to control how much fuel to inject in normal operation.

 

The downstream O2 sensors (after the cat's) are only used to determine if the cat's are still functioning properly.

Thanks. I do appreciate your help!