New Holland 123 – Engine ECM: Boost Pressure Sensor Voltage Too Low

The Engine Control Module (ECM) has detected that the voltage signal from the boost pressure sensor is below the expected minimum threshold. The boost pressure sensor measures the air pressure within the intake manifold, which is critical for the ECM to calculate the correct air-fuel mixture, control ignition timing, and manage turbocharger operation. A low voltage reading suggests a potential open or short circuit to ground in the sensor's wiring or a failure of the sensor itself. This condition may affect engine performance and monitoring, often leading to an engine power derate.

• T6
• T7
• T8
• T9
• TG
• TJ
• MX Series
• CX860
• CX880
• MAXXUM

1. 1

   Check for multiple active fault codes (such as code 187 for Sensor Supply 2 Voltage), which can indicate a broader electrical or sensor power supply issue.

2. 2

   Visually inspect the boost pressure sensor's electrical connector and the related engine wiring harness for damage, dirt, debris, moisture, pushed-back or expanded pins, damaged seals, or compromised wire insulation.

3. 3

   Perform a Key On, Engine Off (KOEO) check using a diagnostic scan tool to compare the Manifold Absolute Pressure (MAP), Barometric Pressure (BARO), and Exhaust Back Pressure (EBP) sensor readings. They should all read atmospheric pressure (approx. 14.7 psi) and be within 0.1-0.2 psi of each other.

4. 4

   Inspect all boost and vacuum lines for cracks or loose fittings. Spray a detergent-based solution on the lines and connections to check for bubbling, which indicates a vacuum leak.

1. 1

   Inspect sensor and harness connector

   Turn the keyswitch OFF. Disconnect the engine harness from the boost pressure sensor. Inspect the connector pins on both the harness and the sensor for damage or corrosion. Clean or repair as necessary.

2. 2

   Test sensor supply voltage

   Turn the keyswitch ON. Using a multimeter, check the voltage between the supply wire and the ground/return wire in the harness connector. The voltage should be approximately 5V. If the supply voltage is not present, there is an open or short in the supply or return circuit of the engine harness, or a fault with the ECM.

3. 3

   Test signal circuit

   If the supply voltage is correct, reconnect the harness to the sensor. With the keyswitch ON and the engine running, back-probe the signal wire at the sensor connector. At idle, the voltage should be approximately 0.9V - 1.8V (for CX models, expect 0.9-1.1V at 450-550 RPM, and 1.0-1.3V at 2660 RPM). When throttle is applied, voltage should rise to 3.0V or higher under boost. If the signal voltage is stuck at or near 0V, is out of range, or does not change with engine speed, the sensor is likely faulty.

4. 4

   Replace boost pressure sensor

   If the wiring and supply voltage are confirmed to be good, but the sensor signal is incorrect, replace the boost pressure sensor.

5. 5

   Clear fault codes

   After repair, clear the fault codes using a diagnostic tool and run the machine to verify that the fault does not reappear.