Case IH 123 – Engine Control Module (ECM): Boost Pressure Sensor voltage is too low

The Engine Control Module (ECM) has detected the signal voltage from the Boost Pressure (Intake Manifold Pressure) Sensor is out of range low (typically less than 0.26 VDC for more than 1 second). This means there is either an open circuit, a short to ground in the signal wire, or the sensor has failed internally. When this code is active, the ECM will use a default manifold pressure value, which results in a severe engine power derate, disabled Exhaust Gas Recirculation (EGR), and disabled Diesel Exhaust Fluid (DEF) injection.

• MX Magnum
• STX Steiger
• MX Magnum series
• TG series
• Steiger/STX series
• STX 280
• STX 450
• Maxxum T6 series
• Axial-Flow series
• 5130
• 6130
• 7010
• SR130
• SR160
• SV185

1. 1

   Check for active Fault Code 187 (Sensor Supply 2 Voltage is too low) to rule out a 5-volt reference circuit issue

2. 2

   Visually inspect the Boost Pressure Sensor housing and wiring harness connector for physical damage, moisture, corrosion, or pushed-back pins

3. 3

   Disconnect the sensor, turn the keyswitch ON, and measure the voltage between the 5V supply pin and the ground return pin on the harness connector (should read approximately 5 VDC)

1. 1

   Turn off the machine

   Turn the keyswitch to the OFF position and allow the ECM to power down completely.

2. 2

   Test the Harness

   If the 5V supply is missing during your diagnostic check, trace the wiring harness back to the ECM. Look for chafed wires shorting to the engine block or broken wires. Repair the harness as necessary.

3. 3

   Test the Signal Wire

   If the 5V supply and ground are good, check the signal wire for continuity between the sensor connector and the ECM pin. Ensure the signal wire is not shorted to ground.

4. 4

   Replace the Sensor

   If the wiring harness tests perfectly (good 5V supply, good ground, and unbroken signal wire), the Boost Pressure Sensor has failed internally and must be replaced.

5. 5

   Validate the Repair

   Install the new sensor and reconnect the harness. Turn the keyswitch ON, start the engine, and let it idle for at least 1 minute. Connect your diagnostic tool to verify that Fault Code 123 has changed from ACTIVE to INACTIVE. Clear the inactive codes.