Part 3

OPERATION

TOW/HAUL INDICATOR

The tow/haul indicator gives an indication to the vehicle operator when the tow/haul function of the tow/haul switch has been selected, revising the shift schedule of the electronically controlled automatic transmission. This indicator is controlled by a transistor on the Instrument Panel Cluster (IPC) circuit board based upon cluster programming and electronic messages received by the cluster from the PCM over the Controller Area Network (CAN) data bus.

The tow/haul indicator Light Emitting Diode (LED) is completely controlled by the IPC logic circuit, and that logic will only allow this indicator to operate when the IPC 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 IPC transistor. The IPC will turn ON the tow/haul indicator for the following reasons:

- Tow/Haul Indicator Lamp-On Message - Each time the IPC receives an electronic tow/haul indicator lamp-ON message from the PCM indicating that the tow/haul shift schedule has been selected, the indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the PCM, or until the ignition switch is turned to the OFF position, whichever occurs first.

The PCM continually monitors the tow/haul switch to determine the proper outputs to the automatic transmission. The PCM then sends the proper lamp-ON or lamp-OFF message to the IPC. For further diagnosis of the tow/haul indicator or the IPC circuitry that controls the indicator Testing and Inspection.

TRANSMISSION RANGE INDICATOR

The electronic gear selector indicator gives an indication to the vehicle operator of the transmission gear that has been selected with the automatic transmission gear selector lever. This indicator is controlled by the Instrument Panel Cluster (IPC) circuit board based upon cluster programming. The IPC circuitry automatically configures itself for the proper transmission type based upon the hard wired transmission range sensor mux circuit input to the IPC.

The gear selector indicator information is displayed by the odometer/trip odometer Liquid Crystal Display (LCD) unit soldered onto the IPC electronic circuit board, and the LCD will not display the gear selector indicator information after the ignition switch is turned to the OFF position. Each time the IPC is disconnected from battery current for more than about five minutes, it must configure itself for the automatic transmission type that is in the vehicle once it is reconnected to battery current. The IPC circuitry configures the gear selector indicator based upon the following inputs from the transmission range sensor:

- Open Circuit - If the IPC is configured for an automatic transmission and the transmission range sensor mux circuit is open, the IPC circuitry controls the gear selector indicator display based upon an electronic selected gear message received from the Transmission Control Module (TCM) over the Controller Area Network (CAN) data bus. If the Transmission Range Sensor (TRS) mux circuit is open and no electronic selected gear messages are received from the TCM within two seconds, the IPC circuitry will not display any gear selector position until the condition is resolved or until the ignition switch is turned to the OFF position, whichever occurs first.

- Resolved Circuit - If the transmission range sensor mux circuit is resolved, the cluster circuitry controls the gear selector indicator display based upon the resistance value of the hard wired input from the TRS. If the IPC is configured for an automatic transmission with a TRS input and detects a short to ground or an open in the TRS mux input, the IPC circuitry will not display any gear selector position in the LCD display. The short-to-ground and open circuit conditions for the LCD display will continue until the condition is resolved or until the ignition switch is turned to the OFF position, whichever occurs first.

On vehicles with a TCM, the TCM continually monitors the TRS, then sends the proper message to the IPC. On vehicles without a TCM, the IPC continually monitors the hard wired TRS multiplexed input. For further diagnosis of the gear selector indicator or the IPC circuitry that controls this function Testing and Inspection. For further diagnosis of the TRS on vehicles without a TCM, refer to the transmission range sensor service information for the appropriate transmission.

TURN SIGNAL INDICATOR

The turn signal indicators give an indication to the vehicle operator that the turn signal (left or right indicator flashing) or hazard warning (both left and right indicators flashing) have been selected and are operating. These indicators are controlled by transistors on the Instrument Panel Cluster (IPC) electronic circuit board based upon IPC programming, a hard wired multiplex input received by the IPC from the turn signal and hazard warning switch circuitry of the multi-function switch on the turn/hazard switch mux circuit, and electronic messages received from the Body Control Module (BCM) over the Controller Area Network (CAN) data bus.

Each turn signal indicator Light Emitting Diode (LED) is completely controlled by the BCM logic circuit, and that logic will allow this indicator to operate whenever the IPC receives a battery current input on the fused B(+) circuit. Therefore, each LED can be illuminated regardless of the ignition switch position. The LED only illuminates when it is provided a path to ground by the IPC transistor. The IPC will turn ON the turn signal indicators for the following reasons:

- Turn Signal-On Input - Each time the IPC detects a turn signal-ON input from the turn signal switch circuitry of the multi-function switch on the turn/hazard switch mux circuit, it sends the appropriate electronic turn signal switch status messages to the BCM over the CAN data bus. The BCM responds to these messages by controlling a battery voltage output and the flash rate for either the right or left turn signal lamps. The BCM also sends the appropriate electronic messages back to the IPC to control the flash rate of the turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the IPC electronic circuit board that emulates the sound emitted by a conventional turn signal flasher. The turn signal indicators continue to flash ON and OFF until the IPC receives a turn signal-OFF input from the multi-function switch, or until the ignition switch is turned to the OFF position, whichever occurs first.

- Hazard Warning-On Input - Each time the IPC detects a hazard warning-ON input from the hazard warning switch circuitry of the multi-function switch on the turn/hazard switch mux circuit, it sends the appropriate electronic hazard switch status messages to the BCM over the CAN data bus. The BCM responds to these messages by controlling a battery voltage output and the flash rate for each of the right and left turn signal lamps. The BCM also sends the appropriate electronic messages back to the IPC to control the flash rate of the turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the IPC electronic circuit board that emulates the sound emitted by a conventional hazard warning flasher. The turn signal indicators continue to flash ON and OFF until the cluster receives a hazard warning-OFF input from the multi-function switch.

- Lamp Out Mode - If the BCM detects an ineffective turn signal lamp or circuit, it increases the flash rate for the remaining operative turn signals and sends an electronic message to the instrument cluster. The IPC then increases the flash rate of the turn signal indicators and the click rate of the electromechanical relay to provide an indication of the problem to the vehicle operator.

The IPC continually monitors the multi-function switch and electronic messages from the BCM to determine the proper turn signal and hazard warning indicator operation. For further diagnosis of the turn signal indicators or the IPC circuitry that controls the indicators Testing and Inspection.