Case IH 3959 – Engine Control Unit (ECU): Intake Throttle Valve Position is higher than expected

This code indicates a plausibility error monitored by the engine's control system. It triggers when the actual measured position of the intake throttle valve exceeds the position that the system expects or has commanded. This condition typically points to a malfunctioning valve, a failed position sensor, or a wiring harness issue (such as a short to a high source).

• Machines with Perkins engines
• Machines with ISM-DI engines
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• STM N Series Loaders

1. 1

   Disconnect the wiring harness from the ECU and the intake throttle valve.

2. 2

   Test the wiring harness for breaks, damaged conductors, or shorts to a high voltage source.

3. 3

   Evaluate findings: If the wiring harness test fails, locate and repair the damaged conductor. If the wiring harness test passes, the intake throttle valve sensor has likely failed internally.

4. 4

   Inspect the valve physically to ensure it is not jammed or stuck open by carbon buildup or debris.

1. 1

   Preparation

   Turn off the machine and locate the intake throttle valve on the engine's air inlet pipe.

2. 2

   Disconnect Wiring

   Disconnect the harness connector from the intake throttle valve. Note: You will likely need to pull the lock operation portion back to release the connector lock.

3. 3

   Remove Air Duct

   Loosen the clamps and remove the air duct/inlet pipe from the intake throttle valve.

4. 4

   Remove Valve

   Unbolt and remove the intake throttle valve assembly from the engine intake manifold.

5. 5

   Install New Part

   Mount the new intake throttle valve and secure the bolts to the manufacturer's torque specifications.

6. 6

   Reassembly

   Reattach the air duct and securely reconnect the wiring harness connector.

7. 7

   Software Calibration

   Using a Service Diagnostic Tool, clear the fault codes. You must then perform a "Restore Self Learning Parameters" procedure and run an intake throttle valve calibration so the ECU can learn the new valve's end-stops.

8. 8

   Verification

   Operate the machine while monitoring the display to ensure the error has been resolved and does not return.