SECTION 6 ELECTRICAL 389 FAMILY
CONTROL UNIT IDENTIFICATION
This manual provides service information covering models equipped with the multiplexed instrumentation system. Before
attempting to make service repairs, the technician should be knowledgeable about the system design, components,
operation and troubleshooting procedures for diagnosing instrumentation problems.
Vehicle component inputs are sent to the ICU/CECU through the J1939 data bus or conventional wiring. The ICU/CECU
interprets the various inputs and monitors/controls the functions for each input through the ICU/CECU software. Output
signals from the ICU/CECU provide data for the gauges, warning lamps, audible alarms, and displays inside the cluster.
When used in conjunction with the Electronic Service Analyst (ESA) diagnostic software tool, the technician can review
fault codes stored in the ICU/CECU, verify whether the instrumentation is working properly and diagnose the root cause of
the problem more easily.
FUNCTIONAL DESCRIPTION-INSTURMENTATION CONTROL UNIT/CAB ELECTRONIC
CONTROL UNIT (ICU/CECU)
The heart of the multiplexed instrumentation system is the ICU/CECU. The ICU/CECU is located behind the radio at the
center of the dash. See FIGURE 6-1.
This manual provides service information covering trucks equipped with the multiplexed instrumentation system. Before
attempting to make service repairs, the technician should be knowledgeable about the system design, components,
operation and troubleshooting procedures for diagnosing multiplexed instrumentation problems.
