Operation

OPERATION

The primary function of the diesel Engine Control Module (ECM) is to operate the following systems:

- Fuel Delivery and Injection
- Electronic Throttle Control
- Glow Plug
- Emission Control
- Turbocharger
- A/C Compressor
- Starting

The secondary function of the ECM is to provide on-board diagnostics. During engine operation, the ECM monitors engine sensors and their related circuits for signals that are out of the normal range. The ECM constantly compares input signal voltages from each sensor with pre-programmed values (the established high and low limits of the input sensor range). If the input signal voltage is not within the established high and low limits of the input sensor range, a Diagnostic Trouble Code (DTC) will be stored (set) in the ECM memory, where it can be displayed or cleared with a scan tool. If a DTC is related to the engine or emission system, the ECM will send a signal to illuminate the Malfunction Indicator Light (MIL) in the instrument cluster module. Each monitored circuit has an associated set of conditions that the ECM must detect before a DTC will set. It is possible that a DTC for a monitored circuit may not set, even though a malfunction has occurred. This can happen if all conditions for setting the DTC have not occurred. If a DTC is cleared with a scan tool and the conditions that caused it have not been corrected, the DTC will continue to set.

ECM OPERATING MODES

The ECM is programmed to adaptively control engine systems based on the inputs received from engine system sensors. There are several different modes of operation that determine how the ECM responds to the input signals.

Ignition Switch On (Engine Off)

When the Electronic Ignition Switch/Central GateWay (EIS/CGW) is turned to the ON position, it will send the ON signal to the ECM through the CAN-C bus. When the ECM receives the ON signal, it will send a signal through the LIN bus to actuate the glow plug module, which provides battery voltage to the glow plugs. At the same time, the ECM actuates the fuel pump relay, which battery voltage to the in-tank (low pressure) fuel pump. If the engine is not started within approximately 4 seconds of the ECM receiving the ON signal from the EIS/CGW, the ECM will turn off the in-tank fuel pump.

Engine Start-Up Mode

When the EIS/CGW is turned to the START position from the ON position, it will send the ON and START signals to the ECM through the CAN-C bus. When the ECM receives the ON and START signals, and the Gearshift is in neutral or park, the ECM will actuate the Starter Relay, which provides battery voltage to the Starter Solenoid, which actuates the Starter. As the engine cranks, the ECM will use the signals from the Camshaft and Crankshaft Position Sensors to determine when cylinder 1 is at TDC. When the ECM has sensed engine RPM and the TDC position of cylinder 1, it will sequence the actuation of the injectors according to engine firing order. If the camshaft position sensor is not present during engine cranking, the engine will not start.

Idle Speed Control Modes

The ECM constantly monitors the coolant temperature sensor throughout all modes operation. After the engine starts and before the engine coolant reaches a temperature above 80° C (176° F), the ECM will deliver a pre-programmed quantity of fuel to each cylinder by cycling the fuel pressure regulator and the length of time each injector is actuated. When the engine coolant temperature rises above 80° C (176° F), the ECM will maintain idle speed at approximately 700 RPM by adaptively controlling fuel injection timing and quantity based on input signals received from the following sensors:

- Fuel Rail Pressure Sensor
- Boost Pressure Sensor
- Coolant Temperature Sensor
- Charge Air Temperature Sensor
- Intake Manifold Pressure Sensor
- Accelerator Pedal Sensor
- Crankshaft Position Sensor
- Fuel Temperature Sensor
- Transmission Shifter Position

Normal Driving Modes

Because engine load will vary extensively based on vehicle applications, driving conditions and driver requirements, the ECM constantly adapts electronic throttle position, exhaust gas recirculation valve position, fuel injection timing, and injection quantity to deliver the best engine performance, emissions control, fuel economy and torque. For any given operating condition when the engine coolant temperature is above 80° C (176° F), the ECM is programmed to operate in the most effective fuel delivery and injection mode based on input signals from the following sensors and modules:

- Mass Airflow (MAF) Sensor
- Fuel Rail Pressure Sensor
- Boost Pressure Sensor
- Coolant Temperature Sensor
- Intake Manifold Pressure (MAP) Sensor
- Electronic Stability Control Module
- Steering Control Module
- Transmission Control Module

Limp-In Mode

If there is a fault detected with the accelerator pedal position sensor, the ECM will set the engine speed at 1100 RPM.

Overspeed Detection Mode

If the ECM detects engine RPM that exceeds 4500 RPM, the ECM will set a DTC in memory 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.

MONITORED CIRCUITS

The ECM is able to monitor and identify most driveability related trouble conditions. Some circuits are directly monitored through ECM feedback circuitry. In addition, the ECM monitors the voltage state of some circuits and compares those states with expected values. Other systems are monitored indirectly when the ECM conducts a rationality test to identify problems. Although most subsytems of the engine control module are either directly or indirectly monitored, there may be occasions when diagnostic trouble codes are not immediately identified. For a trouble code to set, a specific set of conditions must occur and unless these conditions occur, a DTC will not set.

DIAGNOSTIC TROUBLE CODES

Each diagnostic trouble code (DTC) is diagnosed by following a specific procedure. The diagnostic test procedure contains step-by-step instruction for determining the cause of the DTC as well as no trouble code problems.

HARD CODE

A DTC that comes back within one cycle of the ignition key is a hard code. This means that the problem is current every time the ECM/SKIM checks that circuit or function. Procedures in this manual verify if the DTC is a hard code at the beginning of each test. When the fault is not a hard code, an intermittent test must be performed. NOTE: If the scan tool displays faults for multiple components (i.e. ECT, VSS, IAT sensors) identify and check the shared circuits for possible problems before continuing (i.e. sensor grounds or 5-volt supply circuits). Refer to the appropriate schematic to identify shared circuits. Refer to the appropriate diagnostic information.

INTERMITTENT CODE

A DTC that is not current every time the ECM checks the circuit or function is an intermittent code. Most intermittent DTCs are caused by wiring or connector problems. Problems that come and go like this are the most difficult to diagnose; they must be looked for under specific conditions that cause them. NOTE: Electromagnetic (radio) interference can cause an intermittent system malfunction. This interference can interrupt communication between the ignition key transponder and the SKIM.
The following checks may assist you in identifying a possible intermittent problem:
- Visually inspect the related wire harness connectors. Look for broken, bent, pushed out or corroded terminals.
- Visually inspect the related wire harness. Look for chafed, pierced or partially broken wire.
- Refer to hotlines or technical service bulletins that may apply.

ECM DIAGNOSTIC TROUBLE CODES

IMPORTANT NOTE: Before replacing the ECM for a failed driver, control circuit or ground circuit, be sure to check the related component/circuit integrity for failures not detected due to a double fault in the circuit. Most ECM driver/control circuit failures are caused by internal failures to components (i.e. relays and solenoids) and shorted circuits (i.e. sensor pull-ups, drivers and ground circuits). These faults are difficult to detect when a double fault has occurred and only one DTC has set. If the scan tool displays faults for multiple components (i.e.VSS, ECT, Batt Temp, etc.) identify and check the shared circuits for possible problems before continuing (i.e. sensor grounds or 5-volt supply circuits). Refer to the appropriate wiring diagrams to identify shared circuits. Refer to the appropriate diagnostic information.