System Description

All vehicles are equipped with either a 3.9L (V-6) engine, a 5.2L (V-8) engine, two different 5.9L (V-8) engines, two different 8.0L (V-10) engines, or a 5.9L Cummins in-line 6-cylinder, four-valve-per-cylinder diesel engine.

The 3.9L (V-6) and 5.2L (V-8) engines will be referred to as: LDC (Light Duty Emission Cycle) engines.
- The 5.9L (V-8) gas powered engine will be referred to as either: LDC (Light Duty Emission Cycle) or HDC (Heavy Duty Emission Cycle) engine.
- The 8.0L (V-10) engine will be referred to as either: MDC (Medium Duty Emission Cycle) or HDC (Heavy Duty Emission Cycle) engine.
- The diesel engine will be referred to as: HDC (Heavy Duty Emission Cycle) engine.

Either of the HDC gas powered engines can be easily identified by the use of an engine mounted air injection pump. The 3.9L5.2L/5.9L LDC gas engines, the 8.0L MDC V-10 engine or the diesel engine will not use an air injection pump.

Maintenance requirements for LDC, MDC and HDC emission systems differ because of different load and operating conditions.

SYSTEM DESCRIPTION

Powertrain Control Module (PCM):

Engine Control Module (ECM):

Two different modules are used for powertrain control with the diesel engine. The Powertrain Control Module (PCM) is used primarily for charging system, transmission, and speed control functions. The Engine Control Module (ECM) is used to control the fuel system. The PCM is located in the right/rear of engine compartment. The ECM is bolted to the left side of the engine cylinder block. Refer to either Powertrain Control Module (PCM), or Engine Control Module (ECM) in Fuel System for a list of inputs and outputs for each module.

The PCM and ECM monitor many different circuits in the powertrain system. If the ECM or PCM senses a problem with a monitored circuit often enough to indicate an actual problem, it stores a Diagnostic Trouble Code (DTC) in the ECM's or PCM's memory. With certain DTC's, if the problem is repaired or ceases to exist, the ECM or PCM cancels the code after 40 warm-up cycles. Certain other DTC's may be cancelled after 1 or 2 good "trips". Refer to Trip Definition. DTC's that affect vehicle emissions illuminate the Malfunction Indicator Lamp (CHECK ENGINE lamp). Refer to Malfunction Indicator Lamp.

Certain DTC's will set a "companion DTC" in the opposite control module. This means that after repair, the DTC must be erased from both modules.

Certain criteria must be met before the ECM or PCM will store a DTC in memory. The criteria may be a specific range of engine RPM, throttle opening, engine temperature or input voltage.

The ECM or PCM might not store a DTC for a monitored circuit even though a malfunction has occurred. This may happen because one of the DTC criteria for the circuit has not been met. For example, assume the DTC criteria requires the ECM to monitor the circuit only when the engine operates between 750 and 2000 RPM. Suppose the sensor's output circuit shorts to ground when engine operates above 2400 RPM (resulting in 0 volt input to the ECM). Because the condition happens at an engine speed above the maximum threshold (2000 rpm), the ECM will not store a DTC.

There are several operating conditions for which the ECM and PCM monitors and sets DTC's. Refer to Monitored Systems, Components, and Non-Monitored Circuits.

16-Way Data Link (Diagnostic) Connector Location:

Technicians must retrieve stored DTC's by connecting the DRB scan tool (or an equivalent scan tool) to the 16-way data link connector. Refer to the Diagnostic Trouble Code chart (list). Remember that DTC's are the results of a system or circuit failure, but do not directly identify the failed component or components.

Various diagnostic procedures may actually cause a diagnostic monitor to set a DTC. For instance, disconnecting a relay or removing an electrical connector while the engine is running. When a repair is completed and verified, connect the DRB scan tool to the 16-way data link connector to erase all ECM and PCM DTC's and extinguish the MIL (CHECK ENGINE lamp).

MALFUNCTION INDICATOR LAMP (MIL)
Whenever the Engine Control Module (ECM), or the Powertrain Control Module (PCM) sets a Diagnostic Trouble Code (DTC) for an emission related item, it illuminates the Malfunction Indicator Lamp (MIL). The MIL is displayed on the instrument panel as the CHECK ENGINE lamp. The MIL will only be illuminated for DTC's that affect vehicle emissions.

There are some monitors that may take two consecutive trips" to illuminate the MIL if a DTC has been detected. Refer to Trip Definition for additional information. The MIL will stay on continuously (if key is ON) when the ECM or PCM has entered a "Limp-In" mode or has identified a failed emission component.

The MIL either flashes or illuminates continuously when the PCM detects active engine misfire. Refer to Misfire Monitoring.

Additionally, the ECM or PCM may reset (turn off) the MIL if a previous malfunction (DTC) has not been re-detected after 2 consecutive "trips" have occurred.

The MIL will illuminate at key-on and Will stay Tit for approximately 2 seconds if the engine has not been cranked over. This is done as a bulb check (bulb test).

Refer to the Diagnostic trouble Code charts for a list of emission related and non-emission related DTC's.

SERVICE REMINDER INDICATOR (SRI) LAMP
The Service Reminder Indicator (SRI) lamp is used with the 5.9L HDC V-8 gasoline powered engine only. The lamp is displayed on the instrument panel as the MAINT REQ'D lamp.

The SRI system is incorporated into the powertrain control module (PCM). The PCM records the vehicles mileage and stores it into memory. At that time, the PCM checks for certain mileage trip points. When the current mileage matches one of the trip points, the SRI lamp is activated.

Certain parts are to be replaced, or certain maintenance must be performed at either an indicated mileage or when the SRI lamp remains on when the key is in the ON position. After performing the part replacement or required maintenance, the SRI lamp must be reset to turn the lamp off. Use the DRB scan tool to reset the SRI lamp.

Failure to perform the part replacement or required maintenance and only reset the SRI lamp may be a violation of federal law. Only after performing the part replacement or required maintenance, should the SRI lamp be reset.

STATE DISPLAY TEST MODE
The switch inputs to the Powertrain Control Module (PCM) have two recognized states; HIGH and LOW. For this reason, the PCM cannot recognize the difference between a selected switch position versus an open circuit, a short circuit, or a defective switch. If the State Display screen shows the change from HIGH to LOW or LOW to HIGH, assume the entire switch circuit to the PCM functions properly. Connect the DRB scan tool to the data link connector and access the state display screen. Then access either State Display Inputs and Outputs or State Display Sensors.

CIRCUIT ACTUATION TEST MODE
The Circuit Actuation Test Mode checks for proper operation of output circuits or devices the Powertrain Control Module (PCM) may not internally recognize. The PCM attempts to activate these outputs and allow an observer to verify proper operation. Most of the tests provide an audible or visual indication of device operation (click of relay contacts, fuel spray, etc.). Except for intermittent conditions, if a device functions properly during testing, assume the device, its associated wiring, and driver circuit work correctly. Connect the DRB scan tool to the data link connector and access the Actuators screen.