Your vehicle 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.
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.
The exhaust brake switch must be on. See Diesel Engine Exhaust Brake for more information.
The green exhaust brake/restrictor light below the radio controls will be lit for 10 seconds.
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:
| • | Once engine coolant temperature reaches about 150°F (65°C). |
| • | The intake temperature reaches a certain level. |
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 automatic transmission is shifted out of PARK (P) or NEUTRAL (N). |
| • | The clutch pedal on the manual transmission is pressed. |
| • | Vehicle speed is detected. |
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.
