System Description

Fig. 1 16-Way Data Link (Diagnostic) Connector Location:

Fig. 2 Powertrain Control Module (PCM) Location:

Fig. 3 Engine Control Module (ECM) Location:

EMISSION SYSTEM
Two different modules are used for powertrain control with the diesel engine. The Powertrain Control Module (PCM) is used primarily for charging system, transmission, A/C compressor clutch operation and speed control functions. The Engine Control Module (ECM) is used to control the fuel and emission systems. The PCM is located in the right rear of engine compartment. The ECM is bolted to the left side of the engine cylinder block.

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 (MIL). The MIL is displayed as an engine icon (graphic) on the instrument panel. 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 - 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.

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.