Case IH 19730 – DCU (Dosing Control Unit): Ignition "on" signal K15 – digital input ignition ON not sensed during initialization

The control module did not detect the expected wake-up voltage signal from the ignition switch when the machine was turned on. This indicates a failure in the power-up or power-down sequence.

• Tier 4a
• Case IH Magnum Series 235
• Case IH Magnum Series 255
• Case IH Magnum Series 315
• Case IH Magnum Series 340 (Series 4)
• Case IH STX Steiger Series (350 to 600 horsepower models)

1. 1

   Verify that the batteries are fully charged and that the DCU is receiving proper base voltage. Low voltage can cause relays to behave erratically.

2. 2

   Back-probe the ignition switch connector. Verify that it outputs a consistent 12V signal on the K15 circuit when turned to the "ON" position. A worn switch can cause a momentary voltage drop, triggering the P2530 plausibility error.

3. 3

   Locate the DCU Main Power Relay in the fuse/relay panel. Swap it with a known good relay of the same amperage (e.g., a work light relay) to see if the code changes from active to stored. Test the original relay for sticking contacts (which causes the "shut off too late" P0687 code).

4. 4

   Inspect the wiring harness between the ignition switch, the fuse panel (main relay), and the DCU. Look for chafed wires causing a short to ground or short to battery.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery cable to prevent electrical shorts during repair.

2. 2

   Replace the Faulty Relay

   If the diagnostic checks point to a sticking main relay (Code 19739), remove the faulty ECM/PCM power relay from the power distribution box and install a new OEM relay.

3. 3

   Replace the Ignition Switch (if applicable)

   If the K15 signal was dropping out (Code 19730), remove the dashboard trim surrounding the steering column or side console. Unplug the ignition switch harness, unscrew the retaining nut on the face of the switch, and remove the cylinder. Install the new ignition switch and transfer the lock cylinder if necessary.

4. 4

   Inspect DCU Connectors

   Disconnect the main harness at the DCU. Spray the pins with electrical contact cleaner and ensure no pins are pushed back or corroded, as poor contact can simulate an open circuit (Code 19741). Reconnect securely.

5. 5

   Clear Codes and Initialize

   Reconnect the battery. Turn the ignition key to the "ON" position without starting the engine. Allow the modules to initialize. Connect a diagnostic scan tool to clear the stored DCU codes, then cycle the key off and wait for the complete DCU power-down sequence (listen for the DEF pump purging). Verify the codes do not return.