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2 Pin e-fan harness instructions

2 Pin GM Truck Electric Fan Harness Installation

Your PCM 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 2005+ 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.

The e-fans will function just like the factory intended.

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 PCM 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.

  1. Disconnect Negative battery cable.
  2. The PCM is located next to the battery and is covered with a black plastic shield.

Remove the shield by pulling the sides outward to clear the retaining tabs.

  1. Using a large screwdriver, unfasten the large metal clip securing the PCM.
  2. Then pull up on the plastic retaining tab, you can now release the PCM from its mount.
  3. Using a 7mm socket loosen the two securing bolts holding the PCM connectors.
  4. Once the connectors are removed, use pliers to remove the grey plastic covering from the PCM connector. 
  1. Using a pick, remove the green and blue retainers by pushing the white securing clip on both sides.
  2. Now you can push the two PCM terminals into the correct location. The PCM connector is numbered.  Be sure to slightly lubricate the PCM terminals, it allows the terminals to be easily pushed into the rubber seal.

The terminal must push all the way thru and click into place.  Be sure all terminals are evenly pushed through the connector.
Blue Connector PIN 42 – Blue wire

Green/Red Connector PIN 33 – Green wire

  1. Reassemble
  2. Attach the two power cables to the red junction box on the alternator bracket.
  3. Attach the ground cables to one of the two bolts holding the junction box to the alternator bracket. The ground cables need to be between the alternator bracket and junction box mount to ensure a good ground.
  4. The relays attach to the black plastic PCM cover using the supplied screws.
  5. Secure all wires with supplied wire ties.

Fan Operation stock thermostat:

Low speed ON:  200 /  OFF:  198
High speed ON: 210 /  OFF:  206
For 180deg thermostats, values are roughly 4degs lower than a stock stat.Fan Operation 160deg thermostat:

Low speed ON:  182  /  OFF:  180
High speed ON: 188 /   OFF:  185