Case IH P2D – Engine Control Module (ECM) / Power Control Unit (PCU): Battery Voltage, Open Circuit Or Current Below Normal

The Engine Control Module (ECM) or Power Control Unit (PCU) is detecting that the main battery voltage supply has dropped below the acceptable operating threshold, or there is an open circuit in the power supply wiring.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• TM115
• TM120
• TM125
• TM130
• TM135
• TM140

1. 1

   Check resting battery voltage (should be ~12.6V) and inspect battery terminals for heavy corrosion or loose connections

2. 2

   Inspect Fuse 27 (20A) in the main fuse panel, which protects the ignition and main power circuits

3. 3

   Check the K1 Ignition Relay and K2 Start Relay for sticking or burnt contacts causing a voltage drop

4. 4

   Check alternator output to ensure the charging system is maintaining voltage during operation

5. 5

   Check for an open circuit or short to ground in the harness between the battery, the main power relay, and the ECM connectors

1. 1

   Power Down

   Turn the keyswitch to the OFF position and disconnect the negative battery cable to prevent false multimeter readings or accidental shorts.

2. 2

   Clean and Tighten

   Remove the battery cables, clean the posts and terminals with a wire brush, and reinstall them tightly. A bad connection creates high resistance, dropping the voltage seen by the ECM.

3. 3

   Inspect Fuse 27

   Locate Fuse 27 in the cab fuse box. If it is blown, replace it with a new 20A fuse. If it blows immediately upon key-on, you have a dead short to ground in the harness.

4. 4

   Test the Harness

   Disconnect the main harness at the ECM. Set your multimeter to Ohms (Ω). Measure the resistance of the power supply wires from the fuse panel/relay to the ECM connector. Wiggle the harness while testing; if resistance exceeds 5 Ohms, locate and repair the chafed wire or replace the harness section.

5. 5

   Test Alternator Output

   Reconnect the battery and start the tractor. Measure the voltage directly at the alternator's B+ terminal. It should read between 13.5V and 14.5V. If it matches battery voltage (e.g., 12V or lower) while running, the alternator has failed and must be replaced.

6. 6

   ECM Software

   If the battery, alternator, relays, and wiring harness all test perfectly, the service manual dictates that the ECM software should be re-flashed. If the fault persists after a re-flash, the ECM itself has an internal fault and must be replaced.