Ive had this problem for a good year now, finally found this thread and acted on it. Did the three things suggested here... new check valve, cleaned corrosion from the ground contact, and cleaned contacts on the RCM.

Has anyone else noticed this is related to humidity? I swear when i wash the car or it rains it triggers this code.

I havent driven much since i worked on it earlier this week; ill report back in a week and let you knwo the results up to that point.