Subaru won’t start

Diagnose and fix Subaru won’t start conditions

If you encounter a Subaru no start issue, start by checking for trouble codes. Shops are finding a wiring harness chaffing issue that can result in this condition. If you check for trouble codes and find a U0100 Lost communication with ECM, this may be the fix. But you also find no trouble codes stored.

Check fuse 25 in the underhood fuse box

Fuse 25  powers the ECM, Leak Check Valve, Fuel Injectors, Mass

Anti-abrasive woven polyester electrical tape

Air Flow and Intake Air Temperature Sensors and Purge Control Solenoid Valve. If the fuse is blown, chances are the wiring harness is shorted. The correct way to check is with a multimeter in current draw mode while wiggling the engine harness. However, many time you can simply check the wiring harness where it touches the aluminum engine coolant crossover pipe. There’s a splice in the harness and it can rub through and short.

If you find the chaffed area, open the harness, repair the damage and wrap several rounds of  woven polyester tape around the harness before securing it. Replace fuse 25 and test for cranking and starting.

©, 2019 Rick Muscoplat