Principles of Operation
Steering Column Switches
Principles of Operation
Ignition Switch
NOTE: The Smart Junction Box (SJB) is also identified as the Generic Electronic Module (GEM).
The ignition switch is controlled by the ignition lock cylinder with a key. When the ignition lock cylinder is turned, a mechanical connection positions the ignition switch to the selected position. The available ignition switch positions are:
- OFF
- ACC
- RUN
- START
The ignition will apply battery voltage to various circuits connected to the SJB based on ignition switch position. The SJB will distribute power to multiple circuits throughout the vehicle. The microprocessor internal to the SJB will broadcast an ignition state network message over the Medium Speed Controller Area Network (MS-CAN) and High Speed Controller Area Network (HS-CAN) busses.
Push Button Start System
The push button start system uses an electronic module in place of a conventional lock cylinder operated ignition switch. The Remote Function Actuator (RFA) module applies battery voltage to the same 3 circuits that a conventional ignition switch would use to achieve the 4 standard ignition states. The RFA module receives input from a momentary type start/stop switch mounted in the instrument panel, the Brake Pedal Position (BPP) switch and wireless input form the Intelligent Access (IA) key fob. Changing the ignition state is accomplished by pressing the start/stop switch in combination with the brake pedal. The RFA module uses input form the IA key fob to authorize use of the vehicle.
Intelligent Access (IA) Key Fob
To achieve any ignition state other than OFF, the IA key fob must be present inside the vehicle. The driver need not perform any actions on the IA key fob to operate the push button start system. It is sufficient that the IA key fob is located inside the vehicle when the start/stop switch is pressed. Pressing the start/stop switch triggers radio frequency communication between the IA key fob and the RFA module. If the IA key fob is not present when the start/stop switch is pressed, the push button starting system will not transition from the ignition OFF state and NO FOB DETECTED will be displayed in the message center.
Backup Antenna
If the battery inside the IA key fob is weak, if the IA key fob is damaged or if excessive ambient Radio Frequency Interference (RFI) prevents communication between the RFA and the IA key fob, the backup antenna located in the glove box provides a secondary means for the RFA module to validate the IA key fob and authorize use of the vehicle. The backup antenna uses passive radio frequency identification to exchange signals with the IA key fob, similar to the way a typical encoded Passive Anti-Theft System (PATS) key and transceiver operate. For more information on the IA key fob and backup antenna, refer to Antitheft and Alarm Systems.
Push Button Starting System Message Center Messages
The message center provides instruction for operating the push button start system. The message center can also display warnings that could indicate a potential issue with the push button start system. The following message center messages pertain to the push buttons start system:
- PRESS BRAKE TO START - Momentarily displayed when the start/stop switch is pressed without the brake pedal being applied.
- ACCESSORY POWER ACTIVE - Displayed when the vehicle is in ACC mode.
- SHIFT TO PARK - Displayed when the start/stop switch is pressed to shut off the engine with the transmission selector lever in any position other than park.
- RESTART NOW OR FOB IS NEEDED - Displayed when the start/stop switch is pressed to shut off the engine and the IA key fob is not detected by the RFA module.
- NO FOB DETECTED - Displayed if the IA key fob is not detected by the RFA module. If this message is observed with the IA key fob located inside the vehicle, go to Antitheft and Alarm Systems to diagnose the IA key fob.
- STARTING SYSTEM FAULT - Displayed if the RFA module receives invalid data from the PCM during PATS authentication. If this message is observed, go to Antitheft and Alarm Systems to diagnose the PATS concern.
Remote Function Actuator (RFA) Module Programming
If it is necessary to replace the RFA module, the replacement module must be programmed. The following scan tool functions must be carried out if an RFA module is installed new:
NOTE: All of the following scan tool functions must be completed before the vehicle will start.
- Programmable Module Installation (PMI) - This process configures the new module with specific vehicle information. Refer to Programmable Module Installation (PMI) in Information Bus. Programming and Relearning
- PATS Parameter Reset - This process initiates an exchange of information between the RFA module and the PCM specific to the anti-theft/engine immobilizer feature. A PATS parameter reset must be carried out when either the RFA module or the PCM is replaced. For more information refer to Passive Anti-Theft System (PATS) Parameter Reset-Intelligent Access (IA) in Antitheft and Alarm Systems. With Intelligent Access (IA)
- IA Key Fob Programming - This process programs the IA key fobs to the RFA. If the RFA module is installed new, 2 IA key fobs will have to be programmed before the vehicle will start. For more information, refer to Key Programming Using Diagnostic Equipment-Intelligent Access (IA) in Antitheft and Alarm Systems. Intelligent Access (IA)
Multifunction Switch
The multifunction switch controls the various components (high beam headlamps, flash-to-pass, turn signal and windshield wiper) by grounding certain SJB circuits and wiper motor circuits. When the SJB detects the specific ground, it sends a voltage to the appropriate component to activate it. The SJB controls the high beam headlamps, the flash-to-pass and the turn signals. The high beam headlamp and the turn signal portion are normally open switches that close when activated. The flash-to-pass switch is a momentary contact switch that grounds the SJB high beam headlamp circuit. The windshield wipe and wash functions are controlled directly by the multifunction switch, wiper and washer motor.
For multifunction switch concerns, refer to one of the following:
- For exterior lighting, refer to Lighting and Horns. Testing and Inspection
- For wipers and washers, refer to Wiper and Washer Systems.