Case IH 434 – Engine Control Module (ECM): Unswitched 12 volt supply voltage disconnected without normal key off sequence

The constant (unswitched) battery supply voltage to the control module fell below 6.2 VDC momentarily while the ignition was on, or the module was not allowed to power down correctly. The system requires unswitched battery voltage to be maintained for at least 30 seconds after the keyswitch is turned OFF so it can save fault data, trip information, and maintenance monitor data to its permanent memory.

• MX Magnum
• STX Steiger
• Case IH MX series
• TG series
• Magnum tractors
• Magnum 275
• MX285
• Steiger/STX series
• STX440

1. 1

   Determine if a battery disconnect switch is being used to shut down the engine, or if the switch is being opened within 10 to 30 seconds of turning the ignition key OFF.

2. 2

   Verify that the primary ECM battery voltage does not drop below 6.2 Volts when the keyswitch is turned ON or during cranking.

3. 3

   Check the in-line fuses located in the unswitched battery wires (typically three 7.5-amp fuses and one 20-amp fuse).

4. 4

   Trace the unswitched battery wires from the positive battery terminal to the ECM power supply stub, looking for damaged insulation, shorts to the engine block, or physical tension pulling on the ECM power connector.

5. 5

   Perform a voltage drop test under electrical load to check for good vehicle grounds (battery to block, block to starter post, block to frame, and block to cab).

1. 1

   Correct Shutdown Procedures

   If the fault was triggered by improper use of a battery disconnect switch, instruct the operator to always wait at least 30 seconds after turning the key OFF before opening the battery disconnect switch.

2. 2

   Relieve Harness Tension

   Inspect the ECM power connector. If the wiring harness is putting tension on the connector, relieve the stress by tie-strapping the harness to the L-bracket directly above the ECM power connector.

3. 3

   Repair Wiring and Fuses

   Replace any blown 7.5-amp or 20-amp in-line fuses. Repair or replace any damaged unswitched battery supply wiring.

4. 4

   Clean and Tighten Grounds

   Remove, clean, and properly torque all ground connections (battery to block, block to frame, and cab grounds) to ensure a solid ground path.

5. 5

   Clear the Fault Code

   Reconnect all components, start the engine, and let it idle for 1 minute. Verify that Fault Code 434 is now inactive.