Raider V6-3.7L SOHC (2006)
Speedometer Head: Description and Operation
SPEEDOMETER
DESCRIPTION
A speedometer is standard equipment on all instrument clusters. The speedometer is located in the center of the instrument cluster, between the
tachometer and the minor gauge set. The speedometer consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a
fixed 210 degree primary scale on the gauge dial face that reads left-to-right either from "0" to "120" mph, or from "0" to "200" km/h, depending
upon the market for which the vehicle is manufactured. Each version also has a secondary inner scale on the gauge dial face that provides the equivalent
opposite units from the primary scale. Text appearing on the cluster overlay above the hub of the speedometer needle abbreviates the unit of measure for
the primary scale (i.e.: MPH or km/h), followed by the unit of measure for the secondary scale.
The speedometer graphics are black (primary scale) and blue (secondary scale) against a white field, making them clearly visible within the instrument
cluster in daylight. When illuminated from behind by the panel lamps dimmer controlled cluster illumination lighting with the exterior lamps turned On,
the white gauge dial face appears blue-green with the black and blue graphics silhouetted against the illuminated background and the red gauge needle
still appears red. Gauge illumination is provided by an integral electro-luminescent lamp that is serviced as a unit with the instrument cluster. The
speedometer is serviced as a unit with the instrument cluster.
OPERATION
The speedometer gives an indication to the vehicle operator of the vehicle road speed. This gauge is controlled by the instrument cluster circuit board
based upon cluster programming and electronic messages received by the cluster from the Power-train Control Module (PCM) over the Controller Area
Network (CAN) data bus.
The speedometer is an air core magnetic unit that receives battery current on the instrument cluster electronic circuit board through the fused ignition
switch output (run-start) circuit whenever the ignition switch is in the On or Start positions. The cluster is programmed to move the gauge needle back to
the low end of the scale after the ignition switch is turned to the Off position. The instrument cluster circuitry controls the gauge needle position and
provides the following features:
-
Vehicle Speed Message - Each time the cluster receives a vehicle speed message from the PCM it will calculate the correct vehicle speed reading
and position the gauge needle at that relative speed position on the gauge scale. The cluster will receive a new vehicle speed message and
reposition the gauge pointer accordingly about every 88 milliseconds. The gauge needle will continually be positioned at the relative vehicle speed
position on the gauge scale until the vehicle stops moving, or until the ignition switch is turned to the Off position, whichever occurs first.
-
Communication Error - If the cluster fails to receive a speedometer message, it will hold the gauge needle at the last indication for about three
seconds, or until the ignition switch is turned to the Off position, whichever occurs first. After three seconds, the gauge needle will return to the
left end of the gauge scale.
-
Actuator Test - Each time the cluster is put through the actuator test, the speedometer needle will be swept to several calibration points on the
gauge scale in a prescribed sequence in order to confirm the functionality of the gauge and the cluster control circuitry.
The PCM continually monitors the vehicle speed sensor to determine the vehicle road speed. The PCM then sends the proper vehicle speed messages to
the instrument cluster. For further diagnosis of the speedometer or the instrument cluster circuitry that controls the gauge.
For proper diagnosis of the vehicle speed sensor, the PCM, the CAN data bus, or the electronic message inputs to the instrument cluster that control the
speedometer, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.
