New Holland ENG 3343 – Engine Control Unit (ECU): Power Stage Air Heater 2 Actuator - Signal High

This fault code indicates an electrical issue in the control circuit for the intake air heater (grid heater) relay number 2. Specifically, "Signal High" means the Engine Control Unit (ECU) is detecting a voltage on the actuator control circuit that is higher than expected. This is typically caused by a short to battery voltage (B+) in the wiring harness or an open circuit on a ground-switched control line.

• T8.xxx Series
• T8.275
• T8.300
• T8.390
• CR9090
• CX8080 Elevation
• CX8090 Elevation
• W170B
• W190B
• Magnum 235 - 340 (Series 4)

1. 1

   Inspect the main fuses supplying power to the intake air heater relays and the engine ECU.

2. 2

   Visually inspect the wiring harness between the Engine ECU and the Air Heater 2 Relay for chafed wires shorting to a 12V power source or broken wires causing an open circuit.

3. 3

   Disconnect the Air Heater 2 Relay and measure the resistance across the relay coil pins to ensure it is within the OEM specification (an open coil will often trigger a 'Signal High' code).

4. 4

   With the key ON and the relay disconnected, probe the ECU control wire at the relay connector. If it shows a constant 12V when the ECU is not commanding the heater on, there is a short to power in the harness.

1. 1

   Disconnect Power

   Turn off the battery disconnect switch to prevent accidental shorts when working with the high-amperage grid heater circuits.

2. 2

   Access the Relays

   Locate the intake air heater relays (usually mounted near the engine intake manifold or on the firewall/bulkhead).

3. 3

   Isolate the Fault

   Disconnect the control harness from Air Heater Relay 2.

4. 4

   Repair Wiring

   If the diagnostic tests revealed a short to power or an open wire between the ECU and the relay, trace the harness back to the ECU, open the loom, and repair the damaged wire using weather-sealed splice connectors.

5. 5

   Replace the Relay

   If the wiring tests good but the relay coil is open or internally shorted, unbolt the high-amperage cables from the relay terminals, remove the mounting bolts, and install a new OEM relay. Reattach the cables and torque to specification.

6. 6

   Clear Codes and Verify

   Reconnect the battery, turn the key to the ON position, and use a CNH diagnostic tool (EASy/EST) to clear the ENG 3343 fault code. Cycle the key and verify the code does not return during a cold start sequence.