GM's instructions really added to the confusion by the way they describe the warm-up feature:
Cut and paste from 2011 manual:
The engine has a cold temperature high idle feature which elevates the engine idle speed from base idle to 1050 rpm for pickup models or 1200 rpm for van models when outside temperatures are below 0°C (32°F), and the engine coolant
temperature is below 65°C (150°F).
This feature enhances heater performance by raising the engine coolant temperature faster.
This feature can be turned on or off using the DIC buttons. If the vehicle is not equipped with DIC buttons, do the following to turn this feature on or off:
1. Turn the ignition to ON/RUN, with the vehicle off.
2. Press the accelerator pedal to the floor and hold while quickly pressing the brake pedal three times in less than eight seconds.
3. Release the accelerator pedal and start the engine.
When the engine is started, it will slowly ramp up to the high idle speed after a delay of a few seconds up to approximately
For this method to work properly there must be no throttle or brake pedal faults.
The engine idle speed will return to normal once the following conditions are met:
. Once engine coolant temperature reaches 65°C (150°F).
. Air intake temperature reaches 0°C (32°F).
The high idle speed will be temporarily interrupted and the engine speed will return to normal if any of the following conditions occur:
. The brake pedal is applied.
. The accelerator pedal is pressed.
. The transmission is shifted out of P (Park) or N (Neutral).
. Vehicle speed is detected.
Once these inputs are removed, the engine idle speed will slowly ramp back up to high idle after the normal delay, if the conditions for engine coolant temperature and air intake temperature are still met.
There are separate instructions for the optional Fast/High Idle feature that is operated with the cruise buttons.
2018 GMC 2500 L5P CCSB 4x4 Denali - Mineral Metallic; previous '11 LML, '10 LMM and 04.5 LLY
Last edited by redwngr; 12-14-2019 at 09:59 PM.