Kubota P0687 – Engine Control Module (ECM): Power Relay Coil Short-To-Power

The Engine Control Module (ECM) detects that the voltage on its own power relay control circuit is higher than expected. This indicates that the relay is locked in the closed position (staying active longer than 1 second without a command), the relay pull-in coil is shorted, or there is a short to voltage in the relay driver circuit wiring.

• V3800-CR-TE4
• V3800-CR-TIE4B
• M108X
• WG1605
• WG1605-G-E3
• WG1605-L-E3
• WG1605-GL-E3
• WG-972
• SVL97-3

1. 1

   Swap the main power relay with a known-good relay of the same type from the fuse box to see if the fault clears

2. 2

   Turn the ignition switch to RUN and measure the voltage between terminals 1 and 3 on the relay connector side (or input terminals 4 and 6 on the ECU side) — it should equal battery voltage

3. 3

   Turn the key OFF, disconnect the harness from the ECM, and measure the resistance from the relay output to ground using a multimeter to check for a short

4. 4

   Inspect the relay control circuit wiring between the relay socket and the ECM for chafing or contact with a constant 12V supply

1. 1

   Replace the Power Relay

   If the relay swap test proves the relay is faulty (welded contacts or shorted pull-in coil), replace the ECM/PCM power relay.

2. 2

   Repair the Wiring Harness

   If the voltage is abnormal during testing, trace the wire harness between the relay terminals, the battery, and the ECU. Repair or replace any sections of the harness that have open circuits, damaged insulation, or shorts to voltage.

3. 3

   Clean Ground Connections

   Inspect the main ground connections for the ECM and relay circuit. Clean and tighten any loose or corroded grounds to ensure proper voltage balance.

4. 4

   Replace the ECM

   If the relay is functioning properly, the wiring harness has no shorts or opens, and the voltage reading at the ECU remains abnormal, the ECM's internal relay driver circuit has likely failed. The ECM will need to be replaced and reprogrammed.