I've got this gremlin code 475 that my obd II reads. Says it's the exhaust back pressure valve. I've checked and replaced the exhaust back pressure tube and sensor (caked full of carbon). In the morning when the engines cold I can clear the code, run it and no check engine light. With the engine warm and consecutive starts I go to warm up the glow plugs and the engine light comes on throwing the same code on the OBD ( haven't even turned the starter over yet). It's like it runs a diagnostic with the engine warm and something says 475. My question is why does it only do it when the engines warm? Anything else I can do to trouble shoot and fix this problem?
Thanks
Mike

 

the valve is made in the turbo. Its the throttle plate piece mounted to the back of the exhaust housing. The actuator is in the pedestal.