Main Relay (Computer/Fuel System): Testing and Inspection

Main Relay Failure Symptoms





An open circuit in the Main Relay will result in no voltage to the EMS2000 and the other components as supplied by the Main Relay.

A permanently engaged Main Relay will result in an excessive closed current draw and will lead to a dead battery.

Main Relay activation is monitored by the EMS2000. Faults will be set if the main relay is energized and power is not received by the EMS2000.

Main Relay Testing



- Check Voltage Supply At Battery.
- Test for Voltage at Fuse 34 (With key on).
- Check Voltage at KL 30 of Main Relay.
- Check operation of Relay (Using relay adapter).
- Ground signal from EMS2000.
- Voltage Drops across Relay (Relay Energized and Not Energized).
- Perform TEST PLAN on Power Supply.


Special Tools
When testing the power supply of the EMS2000, the DISplus multimeter function or a hand held multimeter may be used. It is best to make the checks at the EMS2000 connection as this method tests the wiring harness. The correct V-Adapter Cables must be used to ensure the pin connectors and the harness will not be damaged. V-Adapter Cables for the EMS2000 are:

- 40 Pin V-Adapter Cable P/N 12 7 240
- 81 Pin V-Adapter Cable P/N 12 7 250
- Breakout Box (BOB) P/N 61 4 390
- Breakout box (BOB) P/N 61 4 380

When installing the BOB and V-Adapter Cables to the EMS2000 make sure the ignition has been switched off for at least 5 minutes or remove the Main Relay.

Grounds
Multiple ground points are supplied to complete the current path through the EMS2000. Grounds are supplied as constants to sensors or as switched grounds to activate components.

Pins supplying ground to the EMS2000 are:

X6000 - 61,62,80,81
X6004 - 114,115

Generator
A dedicated output from the Generator is provided to the EMS2000 to determine electrical load on the engine. When electrical loads are switched on the generator will require more electrical energy, which will in turn create a greater load on the engine. The output is a PWM modulated signal.

If the PWM signal fails the engine may exhibit poor idle speed stability as the electrical loads are increased.