P1606

SteveSAS

I've seem relays cause issues when they are loose in the car and bouncing around. The shock on the relay will cause the contacts to open for a few milliseconds but is enough to trip a error code. Other cases with age the electromagnet isn't strong enough and any little bump with cause it to open. Easy to find by tapping with a large screw driver with car running. Sometimes corroded connector or faulty crimp. could be many other reasons.
No easy way to fix, you just need to keep looking and rule things out.
At least you now know the area where the issue maybe.