Case IH NH3040 – ECM: HS Power stage cold start heater relay - SOURCE HIGH

The Engine Control Module (ECM) has detected an abnormally high voltage on the control circuit for the cold start heater relay, indicating a short circuit to a positive voltage source. The relay is receiving a signal that is above the expected range even when the ECM has not commanded it to be active. This condition can lead to the grid heater being stuck on or off, which impacts cold weather starting and can potentially cause damage to the heater element or related wiring.

• Magnum
• Magnum 200
• Magnum 215
• Puma
• CX
• Maxxum
• Farmall

1. 1

   Verify battery voltage is around 12.6 volts and ensure all battery terminals and main chassis ground connections are clean and tight.

2. 2

   Locate the cold start heater relay (grid heater relay) and visually inspect it and its connector for signs of corrosion, moisture damage, or melted plastic.

3. 3

   Inspect the wiring harness leading to the relay for any chafing, breaks, or damage that could cause a short to a power source.

4. 4

   With the key off, use a multimeter to check for voltage on the control wire from the ECM to the relay. There should be no voltage present.

5. 5

   Check for continuity between the control wire and the main power supply wires at the relay connector. There should be no continuity.

1. 1

   Disconnect battery

   Disconnect the battery ground cable to prevent electrical shock or further damage before beginning repairs.

2. 2

   Access relay

   Locate and access the cold start heater relay. This may require removing panels or other components depending on the model.

3. 3

   Isolate the fault

   Disconnect the electrical connector from the relay. Clear the fault codes and turn the ignition on without starting the engine. If the fault code does not return, the relay itself is likely faulty. If the fault code returns immediately, the issue is in the wiring harness between the ECM and the relay connector.

4. 4

   Repair wiring harness

   If the fault is isolated to the harness, carefully trace the control wire from the relay connector back to the ECM. Inspect for points where it may be shorted to another wire carrying voltage. Repair any damaged sections and ensure they are properly insulated and secured.

5. 5

   Replace relay

   If the relay is determined to be the cause, replace it with a new OEM or equivalent part. Ensure the new relay is securely seated in its connector.

6. 6

   Reconnect and retest

   Reconnect the battery, start the engine, and clear all fault codes. Allow the engine to run and perform several key cycles to ensure the fault does not reappear.