RAM 2500 Truck 4WD V8-5.7L VIN D (2005)
Electronic Throttle Control Indicator: Description and Operation
An Electronic Throttle Control (ETC) indicator is standard equipment on all gasoline engine instrument clusters. However, on vehicles not equipped
with the I/I optional 5.7 liter gasoline engine, this indicator is electronically disabled. The ETC indicator is located on the right side of the instrument
cluster, to the right of the engine temperature gauge.
The ETC indicator consists of a stencil-like cutout of the International Control and Display Symbol icon for "Electronic Throttle Control" in the opaque
layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. A
red Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the icon to appear in red through the translucent outer layer
of the overlay when the indicator is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board. The ETC
indicator is serviced as a unit with the instrument cluster.
The Electronic Throttle Control (ETC) indicator gives an indication to the vehicle operator when the ETC system is faulty or inoperative. The ETC
indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the
cluster from the Powertrain Control Module (PCM) over the Programmable Communications Interface (PCI) data bus.
The ETC indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this
indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED
will always be off when the ignition switch is in any position except On or Start. The LED only illuminates when it is provided a path to ground by the
instrument cluster transistor. The instrument cluster will turn on the ETC indicator for the following reasons:
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Bulb Test - Each time the ignition switch is turned to the On position the ETC indicator is illuminated for about six seconds. The entire six
second bulb test is a function of the PCM.
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ETC Lamp-On Message - Each time the cluster receives a lamp-on message from the PCM, the ETC indicator will be illuminated. The indicator
can be flashed on and off, or illuminated solid, as dictated by the PCM message. The indicator remains illuminated solid or continues to flash for
about twelve seconds or until the cluster receives a lamp-off message from the PCM, whichever is longer. If the indicator is illuminated solid with
the engine running the vehicle will usually remain drivable. If the indicator is flashing with the engine running the vehicle may require towing. A
flashing indicator means the ETC system requires immediate service.
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Communication Error - If the cluster receives no ETC lamp messages for three consecutive seconds, the ETC indicator is illuminated. The
indicator remains illuminated until the cluster receives a single lamp-off message from the PCM.
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Actuator Test - Each time the cluster is put through the actuator test, the ETC indicator will be turned on, then off again during the bulb check
portion of the test to confirm the functionality of the LED and the cluster control circuitry. The actuator test illumination of the ETC indicator is a
function of the PCM.
The PCM continually monitors the ETC system circuits and sensors to decide whether the system is in good operating condition. The PCM then sends
the proper lamp-on or lamp-off messages to the instrument cluster. If the PCM sends a lamp-on message after the bulb test, it indicates that the PCM has
detected a system malfunction and/or that the ETC system is inoperative. The PCM will store a Diagnostic Trouble Code (DTC) for any malfunction it
detects. Each time the ETC indicator fails to illuminate due to an open or short in the cluster ETC indicator circuit, the cluster sends a message notifying
the PCM of the condition, the instrument cluster and the PCM will each store a DTC.
For proper diagnosis of the ETC system, the PCM, the PCI data bus, or the electronic message inputs to the instrument cluster that control the ETC
indicator, a diagnostic scan tool is required.
