Diesel Electronic Control System; Description - GMC G Service Manual

6E2-6 DIESEL EMISSIONS
DIESEL ELECTRONIC

DESCRIPTION

PURPOSE
The Diesel Electronic Control (DEC) System is used on
the 6.2L (LH6) diesel engine to electronically control the
exhaust gas recirculation system, the Transmission Con­
verter Clutch, and the Cold Advance and Glow Plug
System.
The DEC system has the following components:
• Electronic Control Module (ECM)
• Absolute Pressure (MAP) Sensor
• Coolant Temperature Sensor
• "Service Engine Soon" Lamp Driver Module
• EGR Valve
• EGR Vent Solenoid
• EGR Solenoid
• EPR Valve
• EPR Solenoid
• Throttle Position Sensor
• Engine Speed Sensor
• ALDL Connector
• TCC Solenoid
• Vehicle Speed Sensor
• Cold Advance Relay
• Cold Advance Solenoid
• Glow Plug Relay and Control
• Glow Plugs
Refer to the Exhaust Gas Recirculation (EGR) System
for operational information explaining the ECM control of
the EGR valve and EPR valve.
Refer to Transmission Converter Clutch (TCC) for infor­
mation and diagnosis, when TCC is controlled by the ECM.
Refer to Cold Advance and Glow Plug System for opera­
tion, diagnosis and On-Vehicle Service.
ELECTRONIC CONTROL MODULE (Figures 10
through 12)
The Electronic Control Module (ECM) is located in the
passenger compartment and is the control center of the

Diesel Electronic Control System.

The ECM constantly looks at the information from var­
ious sensors, and controls the EGR, TCC, and Cold
Advance/Glow Plug Systems.
The ECM performs the diagnostic function of the DEC
system. It can recognize operational problems, alert the
driver through the "Service Engine Soon" lamp, and store a
code or codes, which identify the problem areas to aid the
technician in making repairs. Refer to the Diagnosis section
for more information.
The ECM is designed to process the various input infor­
mation, and then sends the necessary electrical responses
to control the above systems.
CONTROL SYSTEM
NOTICE: The ECM must be maintained at a tem­
perature below 85 degrees C (185 degrees F) at
all times. This is most essential if the vehicle is
put through a paint baking process. The ECM
will become inoperative if its temperature
exceeds 85 degrees C (185 degrees F). There­
fore, it is recommended that temporary insula­
tion be placed around the ECM during the time
the vehicle is in a paint oven or other high tem­
perature process.
The ECM is serviced in two parts. Inside the ECM is a
replaceable component called a PROM (Programmable
Read Only Memory), because information can be pro­
grammed into the unit for specific calibrations required for a
specific vehicle/engine combination.
The ECM is supplied without a PROM for service and is
called a Controller. This allows one controller to be used
with several different PROMs.
m HEATER A N D A C M O D U LE
|~2~| RETAIN ER
f~3~1 ELEC TR ON IC C O N TR O L M O D U LE
Figure 10 — ECM Location (R/V Models)
Figure 11 — ECM Location (G-Models)