Problem: The vehicle died while driving on
the highway and was towed to the shop.
Details: When the vehicle was brought into the
shop, the engine would crank over but not start. The tech checked
fuses and found fuse #17 in the engine compartment had blown.
When he tried another fuse, it immediately popped – there was a
dead short to ground. He connected a scan tool to pull diagnostic
trouble codes (DTCs) and found that there was no communication
with PCM, but he could communicate with the TCM. He pulled DTC,
U0100 – Lost Communication with ECM/PCM “A”.
The tech checked the W/R wire for a short circuit – it was good.
He noticed that the main relay was not clicking on or off. After
removing and reinstalling it, the relay began working properly.
Confirmed Repair: The tech replaced the
main relay and #17 fuse, cleared the code and retested. The
engine started right up and did not die on the test drive. When
he checked again after the test drive for DTCs, there were none.