Case IH 74 – Transmission ECM (Power Shuttle ECM): V_12VF_FAILED_LOW 3 Fixed Crit.Dis

The 12-volt reference/sensor supply voltage has failed low. The controller is detecting an abnormally low voltage (or no voltage) on the 12V supply circuit, causing the transmission to enter a limited operating strategy.

• JXC
• JX series
• Farmall series
• TN Series
• TNA Series
• TN60A
• TN70A
• TN75A
• TN85A
• TN95A

1. 1

   Observe if the ECM Calibration/Diagnostic Unit (CDU) or Electronic Service Tool (EST) powers up to verify if the ECM/diagnostic port fuse is blown

2. 2

   Enter CDU diagnostic menus: check H9 menu, channel 15 (value below 428 counts confirms fault) and H5 menu (failure to show 'd20' transition confirms 12V supply failure)

3. 3

   Use a multimeter to check for an open circuit or short to ground between the battery, key switch, fuse block, and ECM Connector 2, Pin 1

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the battery negative lead before servicing the electrical system.

2. 2

   Inspect Fuses

   Locate the tractor's fuse panel and inspect the fuse that supplies power to the Transmission ECM (check the fuse routing to ECM Connector 2, Pin 1). Replace the fuse if it is blown.

3. 3

   Test the Wiring Harness

   If the fuse is intact (or if the new fuse blows immediately), use a multimeter to trace the 12V supply circuit. Test for continuity from the key switch to the fuse, and from the fuse to ECM Connector 2, Pin 1.

4. 4

   Repair Wiring

   If you find a break in the wire or a short to ground (chafed wire touching the tractor chassis), repair the wiring harness using appropriate solder/heat-shrink or replacement pins.

5. 5

   Test the ECM

   If the fuses and wiring harness test perfectly fine, the Power Shuttle ECM has suffered an internal failure and must be replaced.

6. 6

   Recalibrate

   If you replace the Power Shuttle ECM, you must perform the Clutch Pack Calibration procedure (Menu H1) using the CDU or EST before the tractor can be operated.