• 1. Disconnect both batteries
  • 2. Take your terminal connector and attach enough of the supplied wire to reach the location where you plan to mount your switch. You can either soldier the connection or you can crimp the terminal connector to the wire. Be sure this connection doesn't have excess solder or have any pins protruding because it will not fit in the connector hole if it does.
  • 3. Remove the cover from the ECM. It has two plastic tabs holding it on, just pull the cover away from these tabs and it will come off. Note that these tabs are on either side of the plastic holder and may need to be “unlocked” before you can remove the plastic cover.
  • 4. Unhook the metal clip holding the ECM in place. Then push out (thereby unlocking) the two plastic tabs that hold the ECM secure.
  • 5. Unhook the metal clip holding the ECM in. Then push the two plastic tabs that hold the ECM up and push it out. The ECM should now be loose.
  • 6. Rearrange the wiring so you can turn the ECM with the wires facing up. There should be two groups of wires. In between these two groups on the ECM's casting are letters and arrows pointing to 4 different sections on the ECM. Find C1 it should be blue in color. Remove the bolt securing the connections on the side that includes C1. You must remove that entire side, you can not remove just section C1.
  • 7. Coat the connector terminal with dielectric grease and insert it into position 71 on the C1 Connector. You will need to insert a sharp object to pierce the rubber seal on the connector. Push the terminal far enough down and you will feel the lock engage. Pull back slightly to ensure that it ilocked in place. s
  • 8. Re-install the connectors on the ECM being careful to keep the connectors square with the ECM as you tighten the bolts to the correct torque as stated on the connectors.
  • 9. Reinstall the ECM paying special attention to the routing of the wires so that you do not pinch them. Make sure it is secured in its plastic tabs as well as by the metal tab. Reinstall the cover and wire clamps.
  • 10.Take the attached wire, and insert it into the supplied wire loom, and route it into the cab.
  • 11.Attach the wire from the ECM to one side of the SPST toggle switch. Attach a separate length of wire to the other side of the toggle and connect this to 12V ignition hot.
  • 12.Mount the toggle switch in a nice and appropriate place.
  • 13.Reconnect both batteries.

To activate the high idle, turn your switch into the ON position and switch the cruise to the ON position. This should result in an idle of 800RPM. Press the SET button on the cruise and the RPM should climb to 1200. Slide the switch to RESUME and the RPM should be at 1800.

Note if the brake pedal is depresses, or you put the gear selector anywhere but PARK or Neutral or you turn the cruise control switch to OFF the engine will return to normal idle.



  • 1. Poor drivability will result if the high idle switch is left on when driving. The truck will exhibit poor acceleration above 2200 RPM.
  • 2. In 2002, 2003 & 2004 the Duramax is equipped with only two idle speeds. Cruise in SET = 1250 RPM, RESUME = 1800rpm
  • 3. In some instances the high idle feature may need to be activated with a Tech2. Also the idle speeds can also be manipulated or set by the Tech2 as well.
  • 4. Some of the 2500HD/3500 trucks have been manufactured with the PTO connector in place. The PTO connector (if present) should be located behind the airbag disable switch or behind the glove box on the passenger side. It is described as an 8-position connector taped up in one of the above locations.
  • 5. If the PTO connector is present, a PTO accessory kit can be obtained from GM (part#12497678). The PTO accessory kit includes the PTO control switch, PTO interface cable, and instructions. The PTO interface cable is not utilized on the 2500HD/3500 pick-up platform since the interface connector located near the left side (driver’s side) PTO of the Allison 1000 transmission is not present.

If you do have the PTO accessory kit installed you will need to tap into Connector C106 by the fuse control center. Remove the fuse control center for better access. You will need to continue the green wire (pin C) from the male side to the C1-71 pin on the PCM.


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