2.2.278. SPN 520202, FMI 3, ECU internal main relay: Relay1 Short circuit to HIGH SOURCEΒΆ

Description

The high and low power outputs of the ECU are supplied via the main relays (the FET transistors). When a short circuit to ground or battery is detected, the main relays (MR) will automatically shut off. To ensure whether the short circuit to GND or bat is either temporary or permanent, the MR shall be reactivated after the delay time. If the monitoring system detects a continuous short circuit to ground or bat, the MR will be shut off.

Reaction in EEM

The FC is stored and the warning lamp is activated. The CAN message indicates an active fault.

Solution

First save the error log and then do the procedure that follows:

  • Check the DEF heater relay operation.
  • Measure the voltage between the DEF heater relay (the terminal 86) and the engine ground, to see if there is a short circuit to bat.
  • Measure the voltage between the DEF return line heater and the engine ground, to see if there is a short circuit to bat.
  • Measure the voltage between the DEF suction line heater and the engine ground, to see if there is a short circuit to bat.
  • Measure the voltage between the DEF reverting valve (the supply module pin 11) and the engine ground, to see if there is a short circuit to bat.
  • Measure the voltage between the DEF pump motor (the supply module pin 9) and the engine ground, to see if there is a short circuit to bat.