New Holland ENG 3155 – Engine Control Module (ECM / EDC): Grid Heater Relay _Short circuit to Ground

The grid heater is a cold-start assist component that preheats the air in the intake manifold to help the diesel engine start in low temperatures. This code indicates that the control circuit for the grid heater relay has shorted to ground. This is typically caused by a chafed wiring harness touching the machine's chassis, a melted connector, or an internal short within the relay coil itself. When this happens, the grid heater will fail to engage, resulting in hard starting and rough idling in cold weather.

• T6 Series
• T7 Series
• T7.175
• T7.190
• T7.210
• T8 Series
• T8.350
• T9 Series
• T9020
• TJ330
• B-Series Backhoe Loaders
• B90B
• B100B
• B110B
• B115B

1. 1

   Inspect the grid heater relay wiring harness for chafing, melted insulation, or exposed copper touching the frame/ground.

2. 2

   Verify the condition of the grid heater fuses (often a 150 Amp Mega fuse or a specific cab fuse like F21, depending on the model).

3. 3

   Disconnect the harness from the grid heater relay. Use a multimeter to check the control wire running from the ECM to the relay for continuity to ground. If there is continuity, the harness is shorted.

4. 4

   Test the grid heater relay/solenoid itself. If the internal coil is shorted to its casing, the relay is the culprit and must be replaced.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the main battery cables to prevent electrical shock or accidental arcing.

2. 2

   Locate the Relay

   Locate the grid heater relay. Depending on the model, it is usually mounted near the engine air intake manifold, on the front frame, or near the main fuse junction block.

3. 3

   Remove the Faulty Component

   If the wiring harness is shorted, disconnect it from the ECM, relay, and alternator/battery junctions. If the relay is internally shorted, unbolt the heavy-gauge cables and the control wires, then unbolt the relay from its mounting bracket.

4. 4

   Install New Parts

   Install the replacement relay or wiring harness. Ensure all connections are tight and that the new harness is routed away from sharp metal edges or high-heat sources to prevent future chafing.

5. 5

   Reassemble and Test

   Reconnect the battery. Clear the inactive fault codes from the ECM using a diagnostic tool or the onboard display. Cycle the key in cold conditions to verify the grid heater engages (watch for the grid heater dash light or a voltage drop on the battery gauge) without triggering ENG 3155.