Case IH 17591 (F-518408-04) - ECU – Engine Control Module (ECM): Power Relay driver is short circuit to ground only

The control circuit responsible for energizing the main power relay has a direct short to ground. When this occurs, the circuit bypasses its normal load, which can prevent the relay from activating, blow a related fuse, or cause the control module to disable the circuit to protect itself from overcurrent damage.

• VESTRUM CVX
• Farmall 115U Efficient Power Tractor
• Farmall 40-45-50

1. 1

   Inspect the main power relay and its fuse block/receptacle for signs of melting, corrosion, or arcing.

2. 2

   Trace the wiring harness from the power relay back to the ECM. Look for chafed wire insulation, pinched wires against the tractor chassis, or moisture intrusion in the connectors.

3. 3

   Disconnect the battery, remove the power relay, and unplug the ECM connector. Use a digital multimeter to check for continuity between the relay driver control wire and chassis ground. If continuity exists, the short is in the wiring harness.

4. 4

   Test the relay itself to ensure the internal coil has not shorted out.

5. 5

   If the wiring harness tests completely open to ground, verify if the short to ground is an internal failure within the ECM's driver circuit.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the negative battery cable.

2. 2

   Isolate the Short

   Based on the multimeter tests, locate the exact point of the short circuit.

3. 3

   Repair Wiring

   If the wire is chafed and touching the frame, cut out the damaged section. Solder in a new section of wire of the same gauge and seal it with dual-wall heat shrink tubing. Reroute the harness or add protective loom to prevent future chafing.

4. 4

   Replace Relay

   If the relay coil is internally shorted, replace the relay with a new OEM unit.

5. 5

   Replace ECM

   If the wiring and relay are perfectly intact but the driver pin at the ECM is permanently grounded internally, the ECM must be replaced and reprogrammed by a dealer.

6. 6

   Reassembly and Clearing

   Reconnect all components and the battery. Connect the CNH Electronic Service Tool (EST) to the diagnostic port, clear the inactive fault codes, and cycle the key to verify the code does not return.