JCB Tier 4 Engine – Start Relay High Voltage and Current Above Normal

This guide provides steps to resolve high voltage and current issues related to the start relay on JCB Tier 4 engines, specifically for fault codes SPN 1321, FMI 3 and FMI 6 at start-up.

Related Contents:

Start Relay High Voltage Above Normal

Description:

The start relay voltage is detected above the normal operating range.

Possible Causes:

  • Faulty wiring of the start relay.
  • Defective start relay.

Engine Control Module (ECM) Response:

  • The fault code (FC) is stored.
  • The warning light is activated.
  • The CAN bus sends a message indicating an active error.

Solution:

  1. Save and clear the error log.
  2. Restart the ECU.
  3. If the fault reoccurs in the next drive cycle, follow these steps:
    • Inspect the wiring, connectors, and pin contacts for the start relay (look for oxidation or damage).
    • Test with a known-good relay to verify if the original relay is faulty.

Start Relay High Side Current Above Normal

Description:

The start relay’s current is detected above the normal operating range.

Possible Causes:

  • Defective wiring of the start relay.
  • Faulty start relay.

ECM Response:

  • The fault code is saved.
  • The warning light is illuminated.
  • The CAN message indicates an active fault.

Solution:

  1. Save and clear the error log.
  2. Restart the ECU.
  3. If the fault reappears during the next driving cycle:
    • Inspect the start relay wiring, plugs, and pin contact surfaces (oxidation could be an issue).
    • Test the start relay by replacing it with a known-good relay.

By following these steps, you can diagnose and resolve start relay voltage and current issues on JCB Tier 4 engines.