E38 E-fan harness

E38 e-fan harness

E38 – 2 Pin GM Truck 2500 Electric Fan Harness Installation

Your ECM must be programmed for fan activation in order for electric fans to operate correctly.

*NOTICE: If you receive the incorrect harness, please contact Nelson Performance IMMEDIATELY! Any harnesses that are modified or installed will not be replaced/refunded.

PCMs can utilize fan control similar to the 2007/08+ GM vehicles.
The e-fans will function on low and high speed based on coolant temperature and AC line pressure.
Low speed will activate when the low-speed coolant value is met.  If the temperature continues to rise, High speed fan control will activate.  If coolant temp has not activated fan control and the AC is turned ON, once line pressure rises, fan control will be activated.

Before emailing NP for tech assistance, test your harness!
If the harness works as described below, the harness is functioning correctly and the installation is causing the issue.
OR, your ECM is not calibrated correctly for efan operation.

Testing the Harness.  Applying Ground to the Blue efan harness wire will turn both efans on LOW speed.   Applying ground to both the Blue and Green wires will turn both efans on HIGH speed.

The harness is routed so that the relays screw to the inner fender next to the fuse block.  The harness is then routed behind the headlight and down the radiator/efan assembly area.

  • Harness power 12v is attached to the alternator stud.
  • Ground is attached to the alternator bracket/bolt – ground must be touching the alternator bracket.
    The ground eyelets must make contact with the aluminum alternator bracket; underneath the battery junction mounting bracket.
  • Disconnect Negative battery cable.
  • The ECM is located next to the battery.
  • Using a small screwdriver or pick, pull back the red lever locking tab.
  • Then pull up on the connector lever while carefully rocking it back and forth. It may be stuck or tight so be gentle with the lever or connector or it will break.
  • Remove the black ECM connector cover carefully by prying releasing the locking tab where the harness exits.
  • Turn the connector over, using a pick, carefully pry the TPA, Terminal Position Assurance, retainer off.


  • On the top side of the connector, the Pin locations are numbered.
    For ½ ton GM trucks: Low Speed is location X1 – Pin 58, High Speed is X1 – Pin17
    Locate the position and insert the terminals correctly, the terminals are keyed, so insert correctly.
    This is typically the same location for the HD 6.0 GM trucks.
  • Assemble the connector and reconnect the connector to the ECM.

NOTE:  If you truck experiences any issues, DTC’s or malfunctions recheck the installation; something was done incorrectly.

This website uses cookies.