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Error code reference

Mitsubishi Air Conditioner Error Code E.MP

Magnetic pole position unknown

Mitsubishi codesMitsubishi air conditioner codes

Magnetic pole position unknown - rotation command differs from actual motor rotation direction during offline auto tuning.

First step from the service manual

Check for mis-wiring of encoder cable and Pr.359 setting.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What E.MP means on a Mitsubishi air conditioner

The E.MP error code on a Mitsubishi air conditioner indicates that the magnetic pole position of the compressor or fan motor is unknown. This error occurs specifically during offline auto tuning, a process where the inverter drive attempts to characterize the motor's electrical properties before beginning normal operation. The error is triggered when the rotation command issued by the inverter does not match the actual direction of motor rotation detected by the encoder feedback signal. In other words, the drive expects the motor to spin in one direction but detects rotation in the opposite direction, or detects no coherent rotation at all.

The encoder cable is the primary suspect in most E.MP fault situations. If the encoder wiring is reversed, has incorrect phase assignments, or has a loose or broken connection, the inverter receives corrupted positional feedback and cannot establish the magnetic pole reference needed to control the motor. Parameter Pr.359 is also directly involved, as this setting governs how the inverter interprets encoder feedback and motor rotation direction during tuning. An incorrect Pr.359 value can cause a mismatch between commanded and detected rotation even when all physical wiring is correct.

Additionally, internal motor faults such as a damaged encoder disk, shorted motor windings, or a failing encoder sensor can produce the same symptom by generating inaccurate feedback signals. Any mechanical resistance on the motor shaft during the tuning sequence can also prevent normal rotation, causing the inverter to detect a discrepancy between command and actual movement. Resolving E.MP requires methodical verification of the encoder cable wiring, the Pr.359 configuration, and the physical and electrical condition of the motor itself.

Source: manufacturer service documentation.

Common causes of E.MP

  1. 01

    Mis-wired encoder cable

    Wiring / connection

    If the encoder cable connections are reversed or incorrectly phased, the inverter receives rotation feedback that conflicts with the command signal. Inspect the encoder cable for swapped wires, loose terminals, or incorrect connector pin assignments.

  2. 02

    Incorrect Pr.359 parameter setting

    Wiring / connection

    Pr.359 controls how the inverter interprets encoder direction during auto tuning. If this parameter is set to the wrong value, the commanded rotation direction will not match the detected direction even if the wiring is physically correct. Review and correct the Pr.359 setting in the inverter parameter menu.

  3. 03

    Damaged or faulty encoder

    Part replacement

    A physically damaged encoder disk or a failing encoder sensor can produce inaccurate or erratic position signals, causing the inverter to report a pole position conflict. Check for physical damage to the encoder and verify signal output with appropriate diagnostic tools.

  4. 04

    Motor winding fault

    Part replacement

    Shorted or open motor windings can cause the motor to behave unpredictably during the auto tuning sequence, resulting in rotation that does not match the commanded direction. Test winding resistance and insulation integrity to rule out internal motor failure.

  5. 05

    Mechanical obstruction on motor shaft

    Wiring / connection

    If the motor shaft has significant mechanical resistance or is partially seized, the motor may not rotate as commanded during tuning, leading to a mismatch between expected and actual rotation. Inspect the motor and any coupled components for binding or obstruction.

See the test procedure for each cause

Frequently asked questions about E.MP

What does E.MP mean on a Mitsubishi air_conditioner?
E.MP means the inverter drive could not determine the magnetic pole position of the motor during offline auto tuning because the rotation command differed from the actual detected motor rotation direction. This is most often caused by mis-wired encoder cables or an incorrect Pr.359 parameter setting. The system generates this fault to prevent damage from uncontrolled motor operation. A technician must inspect the wiring and configuration before the unit can operate normally.
Can I fix the E.MP error myself?
If you are comfortable working with inverter drive parameters and low-voltage signal wiring, you can check the Pr.359 setting and visually inspect the encoder cable connections for obvious mis-wiring. However, correcting parameter settings incorrectly or working near live inverter components carries a risk of equipment damage or injury, so most homeowners should contact a qualified technician. Diagnosing a damaged encoder or motor winding fault also requires specialized test equipment.
Is it safe to keep using the air conditioner when E.MP is displayed?
No. The E.MP fault locks out motor operation because the inverter cannot safely control the motor without a confirmed magnetic pole position. Attempting to force the unit to run in this condition could damage the motor, the inverter drive, or both. The system should remain off until the fault is diagnosed and resolved.
Will resetting the unit clear the E.MP error?
Resetting the unit will clear the displayed fault code temporarily, but the error will return immediately when the inverter attempts offline auto tuning again if the underlying cause has not been corrected. The mis-wiring or incorrect parameter that triggered the fault must be addressed first. A reset alone is not a repair.
How much does it cost to repair an E.MP error on a Mitsubishi air conditioner?
If the fix is simply correcting the Pr.359 parameter or reseating the encoder cable, the cost is primarily the technician's labor, which typically ranges from around 75 to 200 dollars depending on your location and the service provider. If the encoder sensor itself needs to be replaced, parts and labor combined can range from 150 to 500 dollars or more. A motor replacement represents the higher end of repair costs and can range from several hundred to over a thousand dollars depending on the unit.

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