How to : High idle on '01 and '02 LB7 - Chevy and GMC Duramax Diesel Forum
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Old 11-08-2011, 02:41 PM   eBay Motors  #1 (permalink)
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How to : High idle on '01 and '02 LB7

This is my first attempt at a DIY write up so bear with me.

There is a good write up on this on Kennedy Diesel's page (Kennedy Diesel) that involves running the PTO enable to a toggle switch, another method is to run the wire from the ECM in to the brake switch at hook it up to the green and white wire on the brake switch. My write up does the same thing as running the wire to the brake switch because it ties into the same circuit, but you only have to run the wire from the ECM to the underhood fuse block.

The high idle is achieved through a PTO enable circuit inside the ECM. When hooked to a 12v source, the high idle can be controlled from the cruise control switch. Turning the switch to "standby" will bump the idle to 850rpm. Pushing the "set" button will take the idle to 1250rpm, and hitting the "resume" function will take the idle to 1700rpm. I hooked my PTO enable to the "A/T Shift Lock Control Switch Supply Voltage" circuit that runs from the B/U lamp fuse in the underhood fuseblock to the stop lamp switch. Hooking the PTO enable to this circuit works for the high idle because it takes away the 12v source when the brake pedal is applied and the truck is in gear.

You will need :
- About 3 feet of 20 - 22 gauge wire
- LB7 ECM terminal part # 12084912 (can get them at dealership parts department)
- Terminal crimpers
- 10mm socket
- 7mm socket
- Various sized hook tools and flathead screwdrivers
- Small hook tool or equivalent tool to poke through rubber gasket at ECM connector
- Wire strippers and crimpers
- Electrical tape
- Heat shrink butt connector
- Heat source to shrink the heat shrink

Step one :
Disconnect both batteries to avoid smoking any modules.

Step two :
Disconnect the TCM by removing the two 10mm bolts that hold the cover to the radiator support. Disconnect the connectors fromt the TCM and set it out of the way.



Step three :
Remove the ECM cover and remove the ECM from the mounting bracket (see pic). Next, unbolt both connectors from the ECM. Remove ECM and set it aside. Pull blue connector up towards you to make room to work (blue connector has blue covers on terminals and is the inside connector on the ECM, closest to the power steering pump).



Step four :
Remove the wire cover on the outside of the connector to access the back of the connector.



Step five :
Using terminal crimpers, crimp the ECM terminal to the end of your wire.





Step six :
Puncture the yellow rubber gasket in the back of the ECM connector at terminal # 71 (terminal 71 is the PTO enable pin in the ECM) using a small pick tool, safety pin, needle. Take the terminal and wire that you crimped in the last step and insert it into the back of the ECM connector(you should be able to feel it "click" into place in the connector). Look through the blue terminal protector to make sure the terminal went in all the way.



Step seven :
Cut through the tape that holds the wire loom onto the harness and route the wire towards the underhood fuse block.



Step eight :
remove the underhood fuse block cover. Look for a looped green and black wire in the harness that comes off of the fuse block



Cut the gr/bl wire at the top of the loop and strip both ends.



Strip the end of the wire that you ran from the ECM. Take one side of the wire from the fuseblock and twist the stripped end together with the wire you ran from the ECM. Take the butt connector and put the wire from the fuseblock twisted with the ECM wire, put it into one side and crimp the butt connector. Put the other side of the gr/bl wire in the other side of the butt connector and crimp it down.




Use a heat gun or butane torch to seal the butt connector with the heat shrink tubing. Go back through and tape up the wire loom that you ran the wire through for a clean look.

Step nine :
Reinstall the ECM, TCM and all covers that were taken off. Reconnect the batteries. Start the truck and turn the cruise control to standby, the idle should bump up to around 850rpm. Push the set button at the end of the turn signal switch and the idle should jump to around 1250rpm. Slide the cruise switch to resume and the idle should go to about 1700rpm.

This is a pretty nice mod and is great for cold weather to get the truck up to operating temperature faster. It shouldnt take more than 45 minutes to do start to finish.

Here is a video i took working the high idle through all the settings


If I missed anything or anyone needs more info on how to do this please let me know and I will add it.

'03-'04 LB7's :

The same ECM terminal is used along with the same circuit, but the circuit for the shift lock controls comes out of a different terminal in the underhood fuseblock. The wire is the same color (green/black) as the '01-'02's but comes from terminal A8 in connector 1 of the fuseblock and gets its power from the 10A BTSI fuse.



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Last edited by i_keyser; 09-25-2012 at 07:33 AM.
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Old 11-08-2011, 08:53 PM   eBay Motors  #2 (permalink)
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bump...

added video
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Old 11-08-2011, 10:50 PM   eBay Motors  #3 (permalink)
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I know what I'm doing tomorrow.

Great write up!!!
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Thanks to Brent at Linclon Diesel Specialties. If you need LB7 injectors, check them out.
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Old 11-08-2011, 10:56 PM   eBay Motors  #4 (permalink)
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Wait, I just read the title. This won't work on an '03?
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Thanks to Brent at Linclon Diesel Specialties. If you need LB7 injectors, check them out.
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Old 11-09-2011, 01:01 AM   eBay Motors  #5 (permalink)
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It uses the same ECM terminal on an 03, but im not sure if what he did to tie it into that green/blue wire is the same. You can always just use a switch, run a wire from terminal 71 in the ECm to one side of a switch, and then you just need 12 volts to the other side of the switch. Thats how mine is wired. Turn on switch, hit SET on cruise for 1250 rpm or Resume for 1750 rpm. If you forget and leave the switch on, high idle will go off, but you will be rpm limited to 2000 rpm and you cant go over 55mph.
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Old 11-09-2011, 03:45 AM   eBay Motors  #6 (permalink)
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I did the mod to my 03 yesterday, if I had seen this write up I would of checked to see if it the wiring was there. I ran my wire inside and hooked straight to the green and white wire at the brake pedal switch, works like a dream, and only one wire to run. On the 03's we only get two idle speeds, 1250 and 1700.
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Old 11-09-2011, 04:00 AM   eBay Motors  #7 (permalink)
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Old 11-09-2011, 04:41 AM   eBay Motors  #8 (permalink)
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good write up Ian
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Old 11-09-2011, 07:27 AM   eBay Motors  #9 (permalink)
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Quote:
Originally Posted by gunmetalsi View Post
good write up Ian
thanks man!

ill look at the wiring schematics today and see where the wire runs under the hood for the 03-04 lb7's. im pretty sure the circuit is a little different so it may be in a different place but it will be under there somewhere.

and if anyone is wanting to do this and cant find the terminal at the dealer (parts counter guys can be idiots sometimes) i have a few that i would be willing to ship out. i can even get a few feet of wire to crimp on there too if anyone would be interested.
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Old 11-09-2011, 01:44 PM   eBay Motors  #10 (permalink)
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Quote:
Originally Posted by biketopia View Post
I did the mod to my 03 yesterday, if I had seen this write up I would of checked to see if it the wiring was there. I ran my wire inside and hooked straight to the green and white wire at the brake pedal switch, works like a dream, and only one wire to run. On the 03's we only get two idle speeds, 1250 and 1700.
I'm attempting to do mine right now and my ecm has two separate plugs that each go up to 32. there isn't a number 71 on mine. where did you hook yours to?
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Rancho lift, Rare Parts tie rods, Cognito braces, Isspro boost and EGT, S&B intake, UDP Cat adapter, Air Dog II 165, 35 inch Toyo Open Country MT, 20x10 wheels, MBRP 4 inch Cool Duals, Troll Performance Tuning EFI Live tuned by Kory Willis


Thanks to Brent at Linclon Diesel Specialties. If you need LB7 injectors, check them out.
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