Paccar Kenworth C500 2012, Manual

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8-4
08/12
Section 8
Electrical
Functional Description
Cab Electronic Control Unit (CECU)
The heart of the multiplexed instrumentation system is the Cab Electronic Control Unit (CECU). The CECU is located
behind the center console. See Figure 8-4.
FIGURE 8-4. CECU Location.
Vehicle component inputs are sent to the CECU through the J1939 data bus or conventional wiring. The CECU interprets
the various inputs and monitors/controls the functions for each input through the CECU software. Output signals from the
CECU provide data for the gauges, warning lamps, audible alarms, and displays inside the cluster.
Central Instrument Cluster
The central instrument cluster 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” cards.
Each “telltale” card slides into the left and right sides of the cluster. The standard cards cover most warning light require -
ments; editable cards can be used for less common components that also require warning lights.
The central instrument cluster receives input data from the CECU via the “I-CAN” (see Figure 8-3) data bus. When the
ignition key is first turned ON, the cluster will perform a calibration “power on self-test”. Please see pages 8-18 through
8-20 for more detailed information.
Power On Self-Test
• Ignition key turned ON
• The speedometer and tachometer gauge pointers move from pointing at zero, counter-clockwise to their
mechanical limit (approx. -8°), stay there for one second and go back to pointing at zero
• At the same time, all LED indicators and telltales are switched on together, and then switched off together
• A “Warning” sound sequence is also activated five times without break
The warning lamps in the cluster are all activated by the CECU, except for Telltale Position 5 (usually Refrigerator) and
Position 11 (editable) which are wired directly to the cluster. The CECU receives direct wire inputs for all warning lamps
with the exception of the Low Coolant Level warning and the Traction Control/Stability Control lamp. These lamp inputs
are received via the J1939 (Vehicle CAN) data link. The CECU typically receives the Trailer ABS warnings via the J1939
(Vehicle CAN) data link, however it can also be direct wired to the CECU from the ABS unit on the trailer, if required. See
Figure 8-5 below.