Case IH 13021 – Universal Control Module (UCM) / MFD / Instrument Controller (INST): Supply voltage 12VS2 - voltage too low OR Transmission Oil Temperature sensor voltage is too low

Depending on the controller, this indicates either the 12VS2 power supply rail has dropped below the minimum voltage threshold (often a blown fuse or wiring issue), or the transmission oil temperature sensor signal voltage is too low due to a short to ground or failed sensor.

• MAXXUM T4E
• Puma series (e.g., Puma 210)
• Magnum series (e.g., Magnum 235-340, MX series)
• Steiger series
• Planters utilizing the Pro 1200 display and UCM

1. 1

   If diagnosing 12VS2 supply cause: Check the tractor's main system voltage to ensure the batteries and alternator are functioning correctly (look for accompanying codes like 1015).

2. 2

   If diagnosing 12VS2 supply cause: Locate the fuse panel and inspect the specific fuse protecting the 12VS2 circuit.

3. 3

   If diagnosing 12VS2 supply cause: Check the power input pins at the Universal Control Module (UCM) or MFD controller with a multimeter to verify if voltage is actually reaching the module.

4. 4

   If diagnosing INST transmission temp cause: Disconnect the transmission oil temperature sensor and check the sensor's internal resistance with a multimeter.

5. 5

   If diagnosing INST transmission temp cause: Inspect the wiring harness from the instrumentation controller to the transmission oil temperature sensor for chafing or a short to ground.

1. 1

   Connect the Electronic Service Tool (EST) to verify the active fault code and check for any other low voltage codes.

   If diagnosing 12VS2 supply cause

2. 2

   Access the main fuse/relay panel. Locate the fuse designated for the 12VS2 power supply (refer to the specific operator's manual for the fuse layout of your exact model).

   If diagnosing 12VS2 supply cause

3. 3

   If the fuse is blown, replace it with a fuse of the exact same amperage rating.

   If diagnosing 12VS2 supply cause

4. 4

   If the fuse blows again immediately, trace the 12VS2 wiring harness from the fuse block to the UCM/MFD controller to locate the short to ground. Repair the damaged wire.

   If diagnosing 12VS2 supply cause

5. 5

   If the fuse is intact but voltage is low at the controller, clean the harness connectors and check for excessive resistance in the power wire.

   If diagnosing 12VS2 supply cause

6. 6

   Clear the fault code and test operate the machine.

   If diagnosing 12VS2 supply cause

7. 7

   Locate the transmission oil temperature sensor on the transmission housing.

   If diagnosing INST transmission temp cause

8. 8

   Disconnect the sensor pigtail. If the fault code changes to 13022 (voltage too high / open circuit), the wiring is likely intact and the sensor itself has failed internally (shorted).

   If diagnosing INST transmission temp cause

9. 9

   Replace the transmission oil temperature sensor.

   If diagnosing INST transmission temp cause

10. 10

    If the code remains 13021 with the sensor unplugged, trace the signal wire back to the Instrument Controller and repair the short to ground in the harness.

    If diagnosing INST transmission temp cause