Exhaust Restrictor Engine Warm-Up

Exhaust Restrictor

If the vehicle has a Isuzu 6H Diesel Engine, it may have a feature called an Exhaust Restrictor (NPE), which uses an air actuated valve in the exhaust system to restrict exhaust gas flow which enhances the engine and heater warm-up.

Automatic Quick Warm-Up

If the vehicle has a DURAMAX® 6600 engine, it has a feature called an Automatic Quick Warm-Up, which uses the turbocharger to restrict the exhaust gas flow which enhances the engine and heater warm-up.

In both systems, exhaust restrictor or automatic quick warm-up, the cold temperature high idle feature elevates the engines idle speed, up to 1500 rpm, and restricts the exhaust gas flow, when outside temperatures are below 50°F (10°C), and the engine coolant temperature is below certain levels. This feature enhances heater performance by raising the engine coolant temperature faster.

For all engines this feature is already turned on. The automatic quick warm-up on the DURAMAX® engine can be turned off and on by doing the following procedure:

1. Turn the ignition to ON/RUN, with the vehicle off.
2. Press the accelerator pedal to the floor and hold it while quickly pressing and fully releasing the brake pedal three times in less than eight seconds.
3. Release the accelerator pedal and start the engine. The green exhaust brake/restrictor light below the radio controls will be lit for 10 seconds.

If this feature is turned off, by doing the procedure described previously, and then the engine is started, the exhaust brake/restrictor light will flash for 10 seconds and then it will turn off.

When the engine is started, it will slowly increase to the high idle speed after a delay of a few seconds; up to about two minutes. For this method to work properly there must be no throttle or brake pedal faults, and the throttle pedal must not fall below 75 percent of wide open throttle while pressing the brake pedal.

The engine idle speed will return to normal once the following conditions are met:

The high idle speed will be temporarily interrupted and the engine speed will return to normal if any of the following conditions occur:

Once these conditions no longer exist, the engine idle speed will slowly increase to high idle after the normal delay, if the conditions for engine coolant temperature and air intake temperature are still met.