LML / LGH Duramax Diesel

(2011 - 2016)

Injector Return Line Plug

(Replaces GM CH-50377 / CH50377-A)

A GM Essential Tool for diagnosing low rail pressure

In the event of a rail pressure control issue (typically low rail pressure) on an LML or LGH Duramax, GM test procedure specifies that an injector return line plug (GM special tool # CH-50377) be used as part of the diagnostic process. One possible cause of low rail pressure is an injector that is returning too much fuel back to the return rail and fuel tank.

In the event of a no-start scenario with low rail pressure, GM recommends electrically unplugging each injector one at a time, removing the return line from the injector, plugging the open point on the return line with a return line plug, and then cranking the engine for 15 seconds.  If any fuel is observed to flow from the injector return port, the injector is recommended to be replaced.

In the event that the engine runs but actual rail pressure is less than desired, it is recommended to test for excessive injector return flow with the engine idling. In order to do this it is absolutely necessary to use an injector return line plug to seal any open connections on the return rail. LML/LGH Duramax injectors require a minimum of 43 PSI back pressure on the return side in order to function. If less than 43 PSI is present, the injector will not fire and the engine will not run.  The test is performed by using a graduate to measure the return flow from each injector while idling the engine for one minute. Any injector that exceeds the specified return flow volume or is substantially higher than the others should be replaced.