New Holland 187 – Engine ECM: Sensor Supply 2 Voltage is too low

The voltage provided by the Engine Control Module (ECM) to the 'Sensor Supply 2' 5-volt regulated circuit is below the normal operating range. This circuit powers several engine-related sensors, frequently associated with the SCR/DEF system on modern engines. When low voltage is detected, the ECM logs the fault and may put the engine into a derated limp mode to prevent damage. The underlying cause is typically a short circuit to ground, a faulty sensor pulling the voltage down, a damaged wiring harness, or an internal ECM power supply failure.

• T7.220
• T7.235
• T7.250
• T7.260
• T7.270
• T8.xxx
• Magnum 235
• Magnum 340
• C345
• T190

1. 1

   Verify battery and charging system voltage (must be above 12.5V) as low overall voltage can trigger erroneous sensor faults

2. 2

   Inspect fuses related to the engine controller or auxiliary components (e.g., check for a blown 25-amp 'ALT and KITS' fuse)

3. 3

   Identify sensors on the Sensor Supply 2 circuit (often SCR/DEF system sensors like UREA pressure sensors in the Dosing Control Unit)

4. 4

   Perform component isolation by unplugging sensors on the affected circuit one by one with the key ON (engine off) to see if the fault code returns

5. 5

   Visually inspect the engine wiring harness and connectors for chafing, melting, pinching, corrosion, or bent pins

1. 1

   Confirm the Fault

   Use the tractor's onboard diagnostics or an Electronic Service Tool (EST) to confirm that fault code 187 is active and note any accompanying P-codes (e.g., P204C or P204A).

2. 2

   Perform Diagnostic Checks

   Follow the diagnostic steps to isolate the root cause to a specific sensor or a section of the wiring harness.

3. 3

   Repair or Replace the Faulty Component

   If a sensor is faulty, replace it with a new OEM part. If the wiring harness is damaged, splice in a new section of wire with sealed connectors for minor issues, or replace the complete harness for extensive damage.

4. 4

   Clear Fault Codes

   After the repair is complete, use the diagnostic tool or the vehicle's interface to clear all active and inactive fault codes.

5. 5

   Verify the Repair

   Operate the machine under normal conditions to ensure the fault code does not reappear.