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:
- Save and clear the error log.
- Restart the ECU.
- 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:
- Save and clear the error log.
- Restart the ECU.
- 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.