Check Engine Light All Code H

[RICK'S C5]

I am a bit perplexed.......got a check engine light after standing at a downward angle with the engine running for a few minutes....won't go away. All gages look great.......under hood....no detectable problems. Fluids are all in order. The codes all read "H" for history. Any suggestions? Bad fuel? Bad O2 censor? I do notice a slight miss at idle cold. I let her set for a few days.......light won't go away.

(1998 C5 40,000 odometer)

 

[c4c5specialist]

HI there,
please post your codes and we might be able to help.
Allthebest, c4c5

 

[RICK'S C5]

HI there,
please post your codes and we might be able to help.
Allthebest, c4c5

I put some Sea Foam in the tank.........drove it to work. Called the local dealer who said bring it in only $80.00 for diagnostic ...it applies to any repair.....On the way there the light goes off. Water in tank?

 

[caddy]

02 sensor?

 

[RICK'S C5]

02 sensor?

My Son suggested that also.................but which one would be the most likely culprit?