ECM Operating Modes

ECM OPERATING MODES
As input signals to the ECM change, the ECM adjusts its response to the output devices. For example, the ECM must calculate a different fuel quantity and fuel timing for engine idle condition than it would for a wide open throttle condition. There are several different modes of operation that determine how the ECM responds to the various input signals.

Ignition Switch On (Engine Off)
When the ignition is turned on the ECM activates the glow plug relay for a time period that is determined by engine coolant temperature, intake air temperature and battery voltage.

Engine Start-Up Mode
The ECM uses the intake air temperature sensor, engine temperature sensor and the crankshaft position sensor (engine speed) inputs to determine fuel injection quantity.

Normal Driving Modes
Engine idle, warm-up, acceleration, deceleration and wide open throttle modes are controlled based on all of the sensor inputs to the ECM. The ECM uses these sensor inputs to adjust fuel quantity and fuel injector timing. EGR valve control is performed using feedback from the oxygen sensor. An oxygen sensor is located in the exhaust manifold to sample oxygen content exiting the engine cylinders. The ECM uses the O2 sensor, along with other sensor inputs, to govern the amount of exhaust gas recirculation to reduce HC (Hydrocarbons) and CO (Carbon Monoxide). Engine coolant is routed through the base of the EGR valve to provide additional cooling of the exhaust gas, which further helps the reductions of emissions. The EGR valve has a self-cleaning function. When the engine is shut off, the EGR valve rotates twice to reduce carbon deposits at the valve seat.

Overheat Production Mode
If the engine temperature is above 105° C (221° F) and vehicle speed is above 40 km/h (25 MPH) the ECM will limit fuel quantity for engine protection.

Limp-In Mode
The ECM utilizes different degrees of engine limp-in. The ECM is able to limit engine rpm, engine power output (turbo boost reduction), activate engine cooling fan or all of these functions based on the type of fault that is detected. Critical engine performance faults such as accelerator pedal position sensor fault will result in a fixed idle speed of approximately 680 rpm regardless of actual pedal position. Other less critical faults will result in power reduction throughout the full range of driving conditions.

Overspeed Detection Mode
If the ECM detects engine RPM that exceeds 5200 RPM, the ECM will set a DTC in memory, limit engine RPM to no more than 2500 RPM, and illuminate the MIL until the DTC is cleared.

After-Run Mode
The ECM transfers RAM information to ROM and performs an Input/Output state check.