Case IH 1901 – VCM / UCM: VCM - VCM Supply Voltage High

The control module is detecting an input power supply voltage that exceeds its maximum safe operational limit. This is typically caused by an overcharging alternator, a short-to-power in the wiring harness, or an internal failure within the module's voltage sensing circuit.

• skid steer
• SSL (Skid Steer Loader)
• CTL (Compact Track Loader)
• SR series
• SV series
• TR series
• TV series
• SR175
• SR250
• SV300
• SV340
• TR270
• TV380
• tractors
• combines

1. 1

   System Voltage Test: Use a digital multimeter to measure the voltage at the battery terminals with the engine OFF (should be around 12.6V).

2. 2

   Alternator Output Test: Start the engine and run it at half-throttle. Measure the voltage at the battery again. If the voltage exceeds 14.5V – 15V, the alternator's internal voltage regulator has failed and is overcharging the system.

3. 3

   Harness Inspection: If the alternator output is normal, disconnect the VCM/UCM harness and test the voltage directly at the module's power supply pins. Look for a short-circuit where a higher voltage line might be bleeding into the VCM supply line.

4. 4

   Ground Check: Inspect the main chassis grounds and the specific ground pins for the VCM. A loose or floating ground can cause erratic voltage readings inside the module.

1. 1

   Address Overcharging

   If the alternator is outputting high voltage during the diagnostic test, replace the alternator. Clear the fault codes and run the machine to verify the code 1901 does not return.

2. 2

   Repair Wiring

   If the alternator is fine but the voltage at the VCM connector is abnormally high, trace the wiring harness back to the fuse/relay panel. Repair any chafed wires that are shorting to another power source.

3. 3

   Replace the VCM/UCM

   If the system voltage is perfectly normal at the battery and at the VCM connector, but the module still logs Code 1901, the module's internal voltage sensor has failed.

4. 4

   Module Replacement

   Disconnect the battery. Remove the mounting hardware securing the VCM/UCM and disconnect the multi-pin connectors. Install the new module.

5. 5

   Reprogramming

   A new VCM/UCM is often blank or requires machine-specific configuration. You will need the Case IH Electronic Service Tool (EST) to flash the correct software and calibrate the module to the machine's specific attachments and hydraulic setup.