Case IH 3343 – Engine Control Unit (ECU) / Engine Controller (CNH EDC): Power Stage Air Heater 2 Actuator - Signal High

This code indicates that the voltage signal from the Power Stage Air Heater 2 Actuator (commonly known as the grid heater relay or intake air heater relay) is too high. This typically points to a short circuit to battery/power in the wiring harness, an open circuit on the ground side, or an internal short within the relay itself.

• Case IH Magnum 235 - 340 (Series 4)
• Case IH Steiger series
• Case IH Puma 150, 185 CVT
• Case IH Patriot Sprayers (e.g., 3230)

1. 1

   Inspect the wiring harness between the Engine ECU and the Grid Heater Relay for chafing, melted insulation, or pinched wires that could cause a short to battery voltage.

2. 2

   Disconnect the grid heater relay and check the pins for corrosion, moisture, or damage.

3. 3

   Using a multimeter, test the control wire from the ECU to the relay for a short to power. Verify that the ground circuit for the relay is intact and not open.

4. 4

   Test the internal resistance of the grid heater relay coil. If the coil is shorted internally, it will cause a 'Signal High' reading at the ECU.

1. 1

   Power Down

   Turn off the machine and disconnect the main battery cables. The grid heater circuit carries very high amperage, making this a critical safety step.

2. 2

   Locate the Relay

   Locate the Grid Heater Relay (Power Stage Air Heater 2 Actuator). On models like the Puma, it is typically mounted near the engine frame bracket or A/C pipe retaining bracket.

3. 3

   Disconnect Wiring

   Disconnect the electrical control connector from the relay. Then, unbolt the high-current cables connecting the battery/circuit breaker to the grid heater.

4. 4

   Remove the Actuator

   Remove the retaining bolts/hardware and detach the defective grid heater relay from its mounting bracket.

5. 5

   Install New Part

   Mount the replacement relay. Reattach the high-current cables (ensure they are torqued to OEM spec to prevent arcing) and plug in the electrical control connector.

6. 6

   Reassemble and Clear Codes

   Reconnect the battery cables. Turn the key to the ON position, use a diagnostic scan tool to clear the 3343 fault code, and cycle the key to verify the code does not return.