A clogged tube can cause headaches with intermittent and sometimes unwanted EBPV operation. The tube is fairly easily removed (it snakes out from under the alternator fairly easily). You can unstop it with some wire rope chucked in a variable speed drill and some carb cleaner. Use the drill and wire rope just like a plumbing snake. Cheers!EPR
The exhaust back pressure regulator (EPR) output from the PCM controls the EPR when the engine is running and engine oil temperature is below 75°C (167°F) and ambient air temperature is below 7°C (45°F). The EPR operates a butterfly valve which controls exhaust back pressure. The back pressure will be controlled during low-load, low-speed conditions. At high-load, high-speed conditions, the back pressure system is disabled. The valve is cycled on/off for every start-up to help prevent sticking of the butterfly valve.
The exhaust back pressure (EBP) sensor measures the pressure in the exhaust system downstream of the turbo outlet and upstream of the exhaust back pressure butterfly valve. This sensor is used in conjunction with the EPR to form a closed loop exhaust back pressure control system. The exhaust back pressure is controlled to make the engine run hotter and thus provide more heat to the coolant for cab heating in cold climates during cold engine operation. Additionally, the EBP sensor is used to diagnose excessive back pressure, for restricted exhaust system concerns.
Engine oil pressure is used to control the butterfly valve position via the closed loop control.