System Description
System DescriptionMICU Control Functions Index
The driver's MICU (built into the under-dash fuse/relay box) is one of the B-CAN components. The driver's MICU controls many systems related to the body controller area and a security system, and also works as a gateway to diagnose the other B-CAN connected ECUs with the HDS. Refer to each system circuit diagram for details.
The driver's MICU also controls the function of these circuits:
- Entry lights control (front individual map lights and ceiling light)
- Exterior lights control (including the daytime running lights control, and auto-headlights off control)
- Horns
- Interlock system
- Keyless entry
- Power door locks
- Power window key-off timer
- Security alarm
- Turn signal/hazard warning lights
- Wiper/washer
Body Controller Area Network (B-CAN) and Fast Controller Area Network (F-CAN)
The body controller area network (B-CAN) and the fast controller area network (F-CAN) share information between multiple electronic control units (ECUs). B-CAN communication moves at a slower speed (125 kbps) for convenience related items and for other functions. F-CAN information moves at a faster speed (500 kbps) for "real time" functions such as fuel and emissions data. To allow both systems to share information, the gauge control module translates information from B-CAN to F-CAN and from F-CAN to B-CAN.
Gateway Function
The gauge control module acts as a gateway to allow both systems to share information. The gauge control module translates information from B-CAN to F-CAN and from F-CAN to B-CAN.
Network "Loss of Communication" Error Checking Function
The ECUs on the CAN circuit send messages to each other. If there are any malfunctions on the network, the LCD display on the gauge control module can indicate the error messages by entering the gauge control module self-diagnostic function.
Self-diagnostic Function (On-board diagnosis)
By connecting the HDS to the data link connector (DLC), the HDS can retrieve the diagnostic information from the driver's MICU via a diagnostic line called K-LINE. The K-LINE is separated from the CAN lines, and connected to the CAN related ECUs. The driver's MICU is a gateway between the HDS and B-CAN related ECUs, and sends B-CAN diagnostic information to the HDS. When doing a function test with the HDS, the HDS sends an output signal through the K-LINE to the driver's MICU. The driver's MICU either relays the request to another ECU, or commands the function its self.
Wake-up and Sleep Function
The multiplex integrated control system has "wake-up" and "sleep" functions to decrease parasitic draw on the battery when the ignition switch is to LOCK (0).
- In the sleep mode, the multiplex integrated control system stops functioning (communication and CPU control) when it is not necessary for the system to operate.
- As soon as any operation is requested (for example, a door is unlocked), the related control units in the sleep mode immediately wake up and begin to function.
- When the ignition switch is turned to LOCK (0), and the driver's door is opened, then closed, there is a delay about 40 seconds before the control unit goes from the wake-up mode to the sleep mode.
- The sleep mode will not function if any door is opened or if a key is in the ignition.
- The draw is reduced from 200 mA to less than 35 mA when in the sleep mode.
NOTE: For Sleep and Wake-up Mode Test, refer to Information Bus/Testing and Inspection/Component Tests and Diagnostic Procedures.
Fail-safe Function
To prevent improper operation, the MICUs have a fail-safe function. In the fail-safe mode, the output signal is fixed when any part of the system malfunctions (for example, a faulty control unit or communication line).
Each control unit has a hardware fail-safe function that fixes the output signal when there is a CPU malfunction, and a software fail-safe function that ignores the signal from a malfunctioning control unit, which allows the system to operate normally.
Hardware Fail-safe Control
Fail-safe function
When a CPU problem or a abnormal power supply voltage is detected, the MICUs move to the hardware fail-safe mode, and each system output load is set to the pre-programmed fail-safe value.
Software Fail-safe Control
When any of the data from the B-CAN circuit cannot be received within a specified time, or an unusual combination of the data is recognized, the MICUs move to the software fail-safe mode. The data that cannot be received is forced to a pre-programmed value.
Driver's MICU
Power Supply Voltage Monitoring Function
Entry Lights Control System (Ceiling Lights, Map Lights, Ignition Key Light)
Collision Detection Signal (CDS)
Key Interlock (A/T)
Rear Window Defogger Timer Operation (With Climate Control)
Rear Window Defogger Timer Operation (With HVAC Control)
Combination Light Switch
Daytime Running Lights
Headlight Auto-OFF Function
Turn Signal/Hazard Warning Lights
Courtesy Light
Wiper
Power Window Relay
Keyless Answer Back
Security Answer Back
Answer Back Response Operation
Power Door Locks
Door Lock Response Operation
Keyless Entry System
Keyless PANIC Operation
Auto Power Door Locks (LOCK operation)
Auto Power Door Locks (UNLOCK operation)
Security Alarm System
Passenger's MICU
Power Supply Voltage Monitoring Function
Courtesy Light (Front passenger's side)
Power Door Locks (LOCK)
Power Door Locks (UNLOCK)
Exterior Lights
Automatic Lighting
Washer Operation
Keyless Buzzer Operation
Power Window Relay Circuit
HDS Inputs and Commands
Certain inputs happen so quickly that the HDS cannot update fast enough. Hold the switch that is being tested while monitoring the Data List.
This should give the HDS time to update the signal on the Data List.
Because the HDS software is updated to support the release for newer vehicles it is not uncommon to see system function tests that are not supported.
Make sure that the most current software is loaded.
