Power Distribution Module: Description and Operation
SMART JUNCTION BOX (SJB)Principles of Operation
The SJB is a multifunction module that controls many of the vehicle systems. Several SJB functions utilize hardwired inputs and/or outputs. The SJB controls the following hardwired functions, using the corresponding inputs and outputs:
In addition, the SJB is involved in other vehicle systems through communication over the CAN. For a detailed list of SJB network inputs and outputs, refer to COMMUNICATIONS NETWORK. Some SJB parameters are programmable. Two types of programmable parameters are available: vehicle configuration and customer preference. For additional information on programmable parameters, refer to PROGRAMMABLE MODULE INSTALLATION. Initial Inspection and Diagnostic Overview
The SJB utilizes a protective circuit strategy for many of its outputs (for example, the headlamp output circuit). Output loads (current level) are monitored for excessive current (typically short circuits) and are shut down (turns off the voltage or ground provided by the module) when a fault is detected. A continuous diagnostic trouble code (DTC) is stored at that time for the fault. The circuit will then reset after an ignition cycle or customer demand of the function (switching the component on, 30-minute battery saver being energized). When an excessive circuit load occurs several times, the module shuts down the output until a service procedure is performed. At the same time, the continuous DTC that was stored on the first failure will not clear by a command to clear the continuous DTCs. The module will not allow this code to be cleared or the circuit restored to normal until a successful on-demand self-test proves that the fault has been repaired. After the on-demand self-test has successfully completed (no on-demand DTCs present), the continuous DTC will have been cleared and the circuit function will return.
Inspection and Verification
1. Verify the customer concern.
2. Visually inspect for obvious signs of mechanical or electrical damage.
Visual Inspection Chart:
3. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
NOTE: Make sure to use the latest IDS or equivalent tester software release.
4. If the cause is not visually evident, connect the IDS or equivalent tester to the data link connector (DLC).
NOTE: The vehicle communication module (VCM) LED prove out confirms power and ground from the DLC are provided are provided to the VCM.
5. If the IDS or equivalent tester does not communicate with the VCM:
- Check the VCM connection to the vehicle.
- Check the IDS or equivalent tester connection to the VCM.
- See COMMUNICATIONS NETWORK. No power to the IDS or equivalent tester or to the diagnose no communication with the IDS or equivalent tester. Initial Inspection and Diagnostic Overview
6. If the IDS or equivalent tester does not communicate with the vehicle: See COMMUNICATIONS NETWORK. No response from the powertrain control module (PCM). Initial Inspection and Diagnostic Overview
7. Carry out the network test
- If the IDS or equivalent tester responds with no communication for one or more modules, see COMMUNICATIONS NETWORK. Initial Inspection and Diagnostic Overview
- If the network test passes, retrieve and record continuous memory diagnostic trouble codes (DTCs).
8. Clear the continuous DTCs and carry out the self-test diagnostics for the SJB.
NOTE: Before carrying out the on-demand self test, make sure that the ignition is in RUN, all the door are closed, the brake pedal is not pressed, the transmission is in NEUTRAL (automatic transmissions) and the clutch pedal is not pressed (manual transmissions).
9. If the DTCs retrieved are related to the concern, see SMART JUNCTION BOX (SJB) DIAGNOSTIC TROUBLE CODE (DTC) INDEX. Instrumentation/Driver Information
10. If no DTCs related to the concern are retrieved, see SYMPTOM TROUBLESHOOTING CHART - SMART JUNCTION BOX (SJB). Symptom Related Diagnostic Procedures