Case IH P69 – Engine Control Module (ECM / ECU): Main Relay Defect, Shorted To High Source

The ECM main relay coil is not switching off after the keystart is turned to the OFF position, or the ECU is detecting unexpected high voltage on the relay's control circuit (short to a high source/battery positive).

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• AFX8010
• TM Series
• CX720
• CX840
• CX860
• CX880
• CX8070
• CX8090

1. 1

   Inspect the engine control module main relay (K7 on MXM or K14 on AFX) to see if the relay coil is mechanically stuck closed.

2. 2

   With the keystart OFF, disconnect the ECU harness connectors and measure the voltage between the relay control pin and ground, wiggling the harness to check for an intermittent short to a high voltage source.

3. 3

   Verify that the crankshaft speed sensor input is not constantly reading high, which can falsely trigger the ECU's relay logic.

4. 4

   If the relay and harness test perfectly, check if the fault lies internally within the Engine Control Module.

1. 1

   Turn the ignition key to the OFF position.

2. 2

   Locate the main fuse and relay box.

   Identify the ECM Main Relay (K7 or K14).

3. 3

   Remove the relay and test it for continuity across the switched pins.

   If there is continuity with no power applied to the coil (meaning the contacts are welded shut), replace the relay.

4. 4

   Check the wiring harness between the relay socket and the ECU.

   If the relay is functioning normally, use a multimeter to look for rubbed or melted wire insulation causing a short to battery positive (12V). Repair or replace the harness section if a short is found.

5. 5

   Clear the fault codes using your service diagnostic tool.

6. 6

   Cycle the key ON and OFF.

   If the code immediately returns and all wiring/relays are confirmed good, the Engine Control Module (ECU) has an internal short and must be replaced.