The Diesel Garage banner

1 - 3 of 3 Posts

Senior Member
1,709 Posts
Discussion Starter #1
Anyone have a PPE high idle switch? I have been looking at them.

Senior Member
188 Posts
I installed mine myself with a $2 switch and a hunk of wire. Does the exact same thing.

Senior Member
188 Posts

1) Terminal GM part #12084913 (5 per package) or GM part #12084912 (10 per package) to add to the ECM at terminal position C1-71.

2) Fifteen feet of 18 or 20-gauge wire. The length of wire needed will be dependent on the location of the high idle switch. The color of the OEM wire for this circuit is LIGHT GREEN, but you can use whatever color you have available. The smaller 20-gauge wire is easier to work with and to add the terminal to the ECM (Engine Control Module) connector. Another length of similar gauge wire is needed for the 12V power lead.

3) (1) Single pole single throw switch (SPST) switch. A simple toggle switch works well for this application. Fancier switches with dependent/independent indicator lights can be used if desired but are not necessary, and require basic knowledge of electrical circuits and wiring to hook up correctly. Since there are many different switching options, these instructions will only cover using a basic SPST switch (toggle).

4) Crimp tool, connectors to attach the wires to your switch, fuse tap, 1A or 2A fuse, and fuse holder. Soldered on connectors may be used instead of crimp on connectors. Split loom tubing, electrical tape, cable ties etc. as needed to clean up the appearance of the installation.

5) A small amount of dielectric grease may be used on the added terminal for moisture resistance.

6) Access to the factory shop manuals is recommended if unexpected questions or problems arise during the installation. The GM factory shop manuals can be purchased online from Helm Inc. at

7) A multimeter will aid in installation, but is not required.


1) Disconnect both batteries by unbolting the GROUND or NEGATIVE (-) cable from each battery. IMPORTANT: The ignition switch must be OFF when removing or reattaching the battery cables or damage to the ECM and/or TCM is possible.

2) Locate the Transmission Control Module (TCM) and the Engine Control Module (ECM). The TCM and ECM are located on the driver’s side (DS) of the engine compartment (see FIGURES 1 and 2)

FIGURE 1: ECM and TCM LOCATION (Driver’s side of engine compartment 2001 Duramax Diesel)

FIGURE 2: TCM LOCATION (Driver’s side of engine compartment 2001 Duramax Diesel)

3) The TCM is attached to the radiator shroud by two 10 mm bolts. Removing the TCM allows easier access to the ECM. Remove the two 10 mm bolts along the top edge of the radiator shroud and unplug the (2) connectors from the TCM. The TCM will remain attached to the cover. Lift up and remove the TCM/TCM cover and place them in a safe location to avoid damage. Handle the TCM carefully and avoid dropping it to prevent damage.

4) Remove the ECM cover. The black plastic ECM cover comes off by releasing two tabs, one tab near the top edge of the cover located rearward, the second tab is on the front lower edge which is hard to get to (and see). Release the top rearward tab first by reaching between the battery and the radiator hose, and pressing very hard. The front lower tab will then release easily. The ECM plastic cover is a tight fit, but will come out. Release the plastic wire loom clip(s) attached to the cover so the ECM cover can be removed.

5) Access to the ECM connectors is made easier by releasing the metal spring latch and the plastic tabs holding the ECM in position.

6) You should be able to see the two 80 pin ECM connectors, C1 (blue) and C2 (red). The blue C1 connector faces the passenger side (PS) of the truck and blue may be marked on that side of the ECM. There is a small red area on the top of the DS connector; this is the red C2 connector.

7) There is a small bolt in the middle of each ECM connector that holds the connector to the ECM. Remove the bolts from the center of each ECM connector C1 and C2. Unplug the ECM connectors C1 and C2 and remove the ECM from the engine compartment. Handle ECM carefully and avoid dropping it to prevent damage. Place the ECM in a safe location.

8) Identify the blue C1 ECM connector. Release the tabs on the wire end of the connector for access to the back of the connector.

9) There are small numbers printed on the connector body to identify the terminal positions. Locate terminal position C1-71 and place a small mark on the connector to facilitate identification of this position. C1-71 is the position to add the terminal for the high idle for the Duramax diesel. For reference, terminal position C1-70 should have a BROWN wire in place. Terminal position C1-72 is empty (at least on 2001 models), and C1-73 should have a BROWN/WHITE wire in that position. The colors of the wires referenced for C1-70, C1-72, and C1-73 are from MY2001 and may be different for the MY 2002 – 2003 vehicles.

10) Prepare the terminal (GM part #12084913 or #12084912) that will be added to the ECM connector C1-71 by crimping or soldering the terminal to 18 or 20-gauge wire. Using smaller 20-gauge wire will make adding the terminal to the connector easier. If solder is used to attach the terminal to the wire, use sparingly and avoid clumping the solder since it will be difficult to properly seat the terminal in the connector body. Apply a small amount of dielectric grease to the wire terminal. The OEM wire color for this circuit is LIGHT GREEN, but any color wire can be used.

11) Using a small pick or other sharp object, puncture the YELLOW insulation from the wire side of the blue C1 ECM connector to correspond to the C1-71 position.

12) Remove the translucent plastic cover over the terminal ends of the ECM blue C1 connector by releasing the tabs on each end.

13) Insert the terminal you prepared above (with wire attached) from the wire side of the blue C1 connector position C1-71.

14) VERY IMPORTANT: Make sure the terminal goes all the way to the edge of the ECM connector to insure proper contact. Use the existing terminals as a guide.

15) Replace the translucent plastic cover over the terminal ends and reassemble the cover over the wire end of the blue C1 connector. Carefully inspect the reassembled ECM C1 connector to make sure all terminals are in the proper location.

16) Route your added wire as desired toward the firewall. Use split loom tubing, electrical tape, and cable ties as needed for an OEM appearance.

17) Reattach the blue C1 and red C2 ECM connectors to their proper location on the ECM. The proper torque valve for the ECM connector bolts is 8 N•M or 70 lb -in. DO NOT OVER TORQUE or damage to the ECM and/or ECM connectors could result.

18) Reattach the ECM and TCM to their proper locations. Remember to plug in the (2) TCM connectors, and attach the TCM using the two 10 mm bolts.

19) Find a place on the firewall to run the added wire into the cab. On the Duramax diesel, a good location is pictured below:


You can also pierce the rubber boot for the main wire harness entry into the cab located below the hydroboost assembly and run the wires into the cab.

20) Find a suitable location in the cab to mount the high idle switch. The metal lip along the bottom of the instrument panel offers a good location to mount a toggle type switch.

21) Find a 12V source. A fuse tap can be used to obtain switched 12V power from the fuse panel accessible when the driver front door is opened. It is recommended to use an in-line fuse (1A or 2A) on this 12V power lead as a precaution. If you want to interface the high idle switch with an aftermarket remote start system, you will need to locate an unswitched 12V source for this step. Suggestions for an unswitched 12V power source include direct wiring to the battery, the wiring harness in the steering column, or the fuse panel on the passenger side accessible when the PS front door is open.

22) Route the 12V power lead and the high idle wire to your switch location and attach the wires to your switch.

23) Double-check all the wiring and connections. Make sure the wires do not interfere with the normal operation of any vehicle components, and will not be pinched or crushed.

24) Reattach the battery cables. IMPORTANT: The ignition switch must be OFF when removing or reattaching the battery cables or damage to the ECM and/or TCM is possible.


1) Start the truck normally using the ignition key. If using a remote start, the high idle may not work unless a 12V unswitched source was used as the power lead to the high idle switch.

2) Set the parking brake. The parking brake MUST be set in manual transmission equipped trucks.

3) Transmission should be in PARK or NEUTRAL for Allison equipped trucks.

4) Transmission must be in NEUTRAL for the 6 speed manual equipped trucks.

5) Vehicle speed must be 0 MPH.

6) The brake pedal or clutch pedal is not depressed.

7) Turn on the high idle switch.

8) Turn on the cruise control switch.

9) The idle speed will increase to the STANDBY speed of ~850 RPM for 2001 Duramax diesel equipped trucks. If you have a 2002 or 2003, you MAY NOT see an increase in the idle speed to 850 RPM at this time.

10) Hit the cruise control SET button. The idle speed will increase to ~1250 RPM for 2001 - 2003 Duramax equipped trucks.

11) Engage the RESUME switch on the cruise control stalk. The idle speed will increase to ~1700 RPM for 2001 - 2003 trucks.

12) If the Duramax engine is cold, it may take a few seconds to a few minutes for the high idle to engage. This is normal operation. Some have reported that it may take a few minutes for the high idle to engage when used for the first time.

13) Stepping on the brake pedal, clutch pedal, or shifting into gear will turn off the high idle. If the brake pedal or clutch pedal is released, the high idle speed will resume.

14) Shifting the Allison back into PARK or NEUTRAL will resume the high idle speed.

  • Like
Reactions: squeeky
1 - 3 of 3 Posts