Electronic Powertrain Control Diagnostics
Overview of the 98+ ECM, PCM, JTEC, systems - Page 1

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From Publication 81-699-97123
1998 Electronic 24 Valve TurboDiesel Powertrain Diagnostics


  The procedures contained in this manual include all the specifications, instructions, and graphics needed to diagnose Powertrain Control Module (PCM) and Engine Control Module (ECM) problems; they are no start (NS), diagnostic trouble code (DTC), and no trouble code (NTC).  The diagnostics in this manual are based on the trouble condition or symptom being present at the time of diagnosis.

When repairs are required, refer to the appropriate volume of the service manual for the proper removal and repair procedure.

Diagnostic procedures change every year. New diagnostic systems may be added; carryover systems may be enhanced. READ THE GENERAL INFORMATION SECTIONS IN THIS MANUAL BEFORE TRYING TO DIAGNOSE A VEHICLE TROUBLE CODE. It is recommended that you review the entire manual to become familiar with new or revised diagnostic procedures.

1.1     System Coverage

This diagnostic procedures manual covers 1998 Dodge Truck vehicles with a JTEC Engine and 4 speed Chrysler Transmission Controller (PCM), and Engine Control Module (Cummins) (ECM).

1.2     Six-Step Troubleshooting Procedure

Diagnosis of the Powertrain system is done in six basic steps:


The Powertrain Control Module (PCM) monitors and controls the speed control, charging, A/C, and automatic transmission. The Engine Control Module.(ECM) monitors and controls the Fuel System.


3.1     General Description

The Dodge Truck engine and Auto Transmission systems have the latest in technical advances.  The on-board OBDII diagnostics incorporated with the PCM and ECM controllers are intended to assist the field technician in repairing vehicle problems by the quickest means.

3.2     JTEC Controller and Operating Modes

3.2.1     Overview

The Jeep-Truck PCM features a multi-processor environment (one 16 bit microcomputer, two 8 bit microcomputers) allowing parallel processing of time critical operations. Dedication of one 8 bit processor (K4) to spark control and the other 8 bit processor (D3) to fuel control allows increases in throughput and reduced software complexity in the 16 bit microcomputer (Z2). The result is increased capability in the Z2 to handle overall strategy implementation, OBDII, and other computation-intensive processes. This approach allows control of ten cylinder engines in running excess of 6,500 RPM.

3.2.2    Hardware Architecture

The design of the PCM can be broken up into about eight major sections. The main microcontroller, a Motorola MC68HC16Z2, is attached to a 256k byte memory device (flash memory) which is programmed after manufacture of the module. (This memory can be reprogrammed at the factory or at a dealership. The MC68HClID3 and MC68HCllK4 micro-computers have memories which are permanently programmed during their manufacture, and therefore cannot be reprogrammed.)

The microcomputers communicate over a bus which allows for rapid transmission of high priority messages. The Z2 executes the primary powertrain control strategy; transmits fuel and spark requirements to the D3 and K4; communicates with outside devices; and processes 14 analog inputs and about half of the one bit inputs and outputs. The D3 microcomputer controls fuel injector timing pulses and a small number of one bit inputs and outputs. The K4 controls spark timing pulses, processes 8 analog inputs and a number of one bit inputs and outputs.

Other major sections of the PCM design include the power supply, input conditioning circuits, output driver circuits,'serial communication interface circuits, and a device which controls ignition coil currents.


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