New Holland NH 3042 – Engine Control Unit (ECU): HS Power stage cold start heater relay - NO SIGNAL

The Engine Control Unit (ECU) is failing to detect a signal from the High-Side (HS) power stage of the cold start heater relay (commonly known as the grid heater relay). This indicates an open circuit, a physically disconnected relay, or a wiring failure between the ECU and the relay.

• T6 series
• T7 series
• T8 series
• TM series
• MXM series

1. 1

   Verify that the cold start heater relay is physically connected

2. 2

   Inspect the high-current fuse protecting the grid heater circuit (often a 200A Mega fuse) to ensure it has not blown

3. 3

   Inspect the wiring harness between the Engine ECU and the grid heater relay for chafing, corrosion, or broken wires

4. 4

   Use a multimeter to check the resistance of the relay coil to ensure it is not open

1. 1

   Disconnect Power

   Disconnect the negative battery terminal to prevent accidental shorts, as the grid heater circuit carries very high amperage.

2. 2

   Locate the Relay

   Locate the grid heater power relay, typically mounted near the engine block or the intake manifold grid heater.

3. 3

   Inspect Connections

   Remove the electrical connectors from the relay. Clean any corrosion from the terminals and ensure the harness connector is tightly seated.

4. 4

   Repair/Replace Harness

   If the wiring harness is damaged or broken, repair the wires or replace the specific harness section (e.g., the grid heater relay harness).

5. 5

   Replace the Relay

   If the wiring is intact but the relay coil is open or internally damaged, unbolt the old relay and install a new OEM replacement.

6. 6

   Reassemble and Clear Codes

   Reconnect the battery. Use a diagnostic tool to clear the NH 3042 fault code from the Engine ECU.

7. 7

   Verify Operation

   Turn the key to the ON position. If ambient temperatures are cold enough to trigger the grid heater, verify that the cold start light illuminates on the dash and that the fault code does not return.