The Bosch diesel injection pumps used by VW in their ALH TDI engines have a fuel shutoff solenoid (N109) which is supposed to cut off fuel to the engine. The engine has been setting a DTC
17946 - Fuel Shutoff Solenoid (N109) P1538 - 35-10 - Open or Short to Ground - Intermittent
This has been a real puzzle to me, I'd assumed that the fuel shutoff solenoid was used to shut down the engine, and the engine has always shutdown reliably. Today I was setting the IQ (injection quantity) in my on going effort to solve the engine's smoking problem (nicotine patches don't help…). As I watched the IQ drop to 0 when coasting in gear it got me thinking – is the fuel cutoff solenoid used to implement the coasting fuel cutoff? Does anybody know?