Case IH t8 – Engine Control Unit (ECU): Ambient Pressure Sensor, Grounded Or Current Above Normal Range

The engine's control system has detected that the electrical signal from the ambient (atmospheric) pressure sensor is out of its expected operating range. Specifically, the circuit is either shorted to ground or drawing excessive current.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• Magnum
• Steiger
• Puma

1. 1

   Determine if your specific engine utilizes an internal (built into the ECU) or external ambient pressure sensor

2. 2

   If equipped with an external sensor: Inspect the sensor's wiring harness and connector for chafed wires, corrosion, or pinched lines that would cause a short to ground

3. 3

   If equipped with an external sensor: Test the 5V reference supply and signal return circuits with a multimeter

4. 4

   If equipped with an internal sensor: Temporarily swap the ECU with a known-good replacement controller to verify if the original ECU's internal sensor is defective

1. 1

   Replace ECU (if internal sensor)

   If the sensor is internal and has failed, replace the Engine Control Unit (ECU). Note: Replacing the ECU is not necessary if the machine is never run in high altitude, as it can often continue to run normally on a default fallback value.

2. 2

   Install new ECU

   Disconnect the battery, remove the chassis and injector harness connectors from the ECU, unbolt the ECU from its heat exchanger mounting, and install the new unit. The new ECU will require dealer programming/calibration.

3. 3

   Disconnect battery (if external sensor)

   For external sensors (Cummins-equipped models): Turn off the machine and disconnect the battery.

4. 4

   Unplug sensor

   Locate the ambient air pressure sensor on the engine harness. Depress the locking tab and unplug the 3-pin connector.

5. 5

   Replace sensor

   Unbolt or unthread the faulty sensor and install the replacement.

6. 6

   Reconnect and clear codes

   Reconnect the harness, reconnect the battery, and clear the fault codes using a diagnostic tool.