Case IH tA – Engine ECU: Ambient Pressure Sensor, Shorted To Low Source

The engine control system is receiving a signal voltage from the ambient (barometric) pressure sensor that has dropped below the minimum acceptable threshold. This is typically caused by a short circuit to ground (the 'low source') either within the sensor itself or in its wiring harness, which may trigger a protective torque reduction of approximately 20%.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• Steiger Series
• Axial-Flow Combines
• AFX8010

1. 1

   Consult the specific machine's engine manual to determine if the ambient pressure sensor is an external component or integrated internally into the Engine ECU.

2. 2

   If the sensor is external, disconnect the sensor's wiring harness and inspect the connector pins for corrosion, moisture, or damage.

3. 3

   Use a multimeter to check the external sensor signal wire for a short to ground. If the wire is shorted to the chassis or the ground wire, the harness is the issue.

4. 4

   If the sensor is internal to the ECU, test the system by plugging in a known-good replacement ECU. If the fault code clears, the original ECU's internal sensor has failed.

1. 1

   Disconnect battery

   Turn off the machine and disconnect the battery ground cable to prevent electrical spikes.

2. 2

   Repair external sensor or wiring

   For an external sensor: Disconnect the wiring harness. If diagnostic checks revealed a short in the wiring, repair or splice the damaged section. If the wiring is intact, remove the faulty ambient pressure sensor and install the replacement part. Reconnect the wiring harness securely.

3. 3

   Replace Engine ECU

   For an internal sensor (EEM3/EEM4 systems): The ECU itself must be replaced or sent to a specialized module repair facility. Remove the ECU mounting bolts, carefully disconnect the main harness blocks, and install the new ECU.

4. 4

   Reconnect battery

   Reconnect the battery ground cable.

5. 5

   Clear fault codes

   Turn the ignition on and use the Electronic Service Tool (EST) or the tractor's H-Menu/Universal Display to clear the inactive fault codes and verify that code 'tA' does not return.