Electrical 389 Family
Peterbilt Motors Company 6-6
HOW MULTIPLEXED INSTRUMENTS WORK
Multiplexed gauges receive signals through the Instrumentation Control Unit/Cab Electronic Control Unit (ICU/ CECU)
located behind the center console. The ICU/CECU receives sensor signals either through the J1939 data bus or via
conventional wiring sending signals from sensors that read actual pressures or temperatures. The ICU/CECU interprets
this data and monitors or controls vehicle operation through the ICU/CECU software. The ICU/CECU then sends data to
the gauges, warning lamps, audible alarms, and displays located inside the gauge clusters. The central instrument cluster
(Figure 6-3) includes the speedometer (including odometer and trip meter) and tachometer (including engine hour meter
and outside temperature display), plus pre-installed standard and/or editable warning light symbols called “telltale decals”
mounted on the “Icon Tray.”
The Icon Tray slides into the bottom of the cluster. The standard Icon Tray covers most warning light requirements;
editable icon lenses can be added for less common components that also require warning lights.
FIGURE 6-3. Central Instrument Cluster
Introduction
This section provides service information covering Peterbilt Conventional 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.
See Figure 6-5.
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.
