Module Communications Network System: Overview Mercury Sable V

Note. The smart junction box (SJB) is also known as the generic electronic module (GEM).

Vehicle communication utilizes both International Standards Organization (ISO) 9141 and controller area network (CAN) communications. ISO 9141 is used for diagnostic use only, and CAN is used for many modules to communicate with each other on a common network. CAN in-vehicle networking is a method for transferring data among distributed electronic modules via a serial data bus. Without serial networking, intermodule communication requires dedicated, point to point wiring resulting in bulky, expensive, complex, and difficult to install wiring harnesses. Applying a serial data network reduces the number of wires combining the signals on a single network. Information is sent to the individual control modules that control each function.

The vehicle has 3 module communication networks

1. ISO 9141
2. Medium speed (MS) CAN
3. High speed (HS) CAN

All 3 networks are connected to the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing one scan tool to be able to diagnose and control any module on the 3 networks from one connector. The DLC can be found under the instrument panel between the steering column and the audio control module (ACM).

Scheme 1

ISO 9141 Network Operation

The ISO 9141 communications network is a single wire network. The ISO 9141 communication network is used only by the PAM (if equipped).

MS-CAN Operation

The MS-CAN communicates using bussed messages. The MS-CAN has an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network allows sharing of information between all modules on the network.

The MS-CAN is a medium speed communication network used for the following modules

1. Accessory protocol interface module (APIM)
2. Audio control module (ACM)
3. Driver seat module (DSM) (if equipped)
4. HVAC module
5. Instrument cluster (IC)
6. Liftgate/trunk module (LTM) (if equipped)
7. Rear entertainment module (RETM) (if equipped)
8. Satellite digital audio receiver system (SDARS) module (if equipped)
9. Smart junction box (SJB)

HS-CAN Operation

The HS-CAN communicates using bussed messages. The HS-CAN uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network allows sharing of information between all modules on the network.

The HS-CAN is a high speed communication network used for the following modules

1. ABS module
2. APIM
3. IC
4. Occupant classification system module (OCSM)
5. PCM
6. Power steering control module (PSCM)
7. Restraints control module (RCM)
8. 4X4 control module (if equipped)

Principles of Operation

Note. The smart junction box (SJB) is also known as the generic electronic module (GEM).

Vehicle communication utilizes both International Standards Organization (ISO) 9141 and controller area network (CAN) communications. ISO 9141 is used for diagnostic use only, and CAN is a method for transferring data among distributed electronic modules via a serial data bus.

The vehicle is equipped with 3 module communication networks

1. ISO 9141
2. Medium speed (MS) CAN
3. High speed (HS) CAN

Normal Operation

The PCM communicates with the scan tool through the high speed controller area network (HS-CAN). Circuits VDB04 (WH/BU) (HS-CAN +) and VDB05 (WH) (HS-CAN -) provide the network connection to the PCM. The PCM shares the HS-CAN with the steering effort control module (SECM), the ABS module, the restraints control module (RCM), the 4X4 control module, the accessory protocol interface module (APIM) and the instrument cluster (IC). Voltage and ground for the PCM is provided by redundant circuits. Circuit CBB47 (GN/BU) provides voltage, and circuit GD113 (BK/YE) provides ground.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. PCM

The ABS module communicates with the scan tool through the high speed controller area network (HS-CAN). Circuits VDB04 (WH/BU) (HS-CAN +) and VDB05 (WH) (HS-CAN -) provide the network connection to the ABS module. The ABS module shares the HS-CAN with the PCM, the steering effort control module (SECM), the restraints control module (RCM), the occupant classification system module (OCSM), the 4X4 control module, the accessory protocol interface module (APIM) and the instrument cluster (IC). Voltage for the ABS module is provided by circuit CBB38 (GY/BU), and ground is provided by circuit GD120 (BK/GN).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. ABS module

The instrument cluster (IC) communicates with the scan tool through the high speed controller area network (HS-CAN) and the medium speed controller area network (MS-CAN). Circuits VDB04 (WH/BU) (HS-CAN +) and VDB05 (WH) (HS-CAN -) provide the HS-CAN connection to the IC and circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the MS-CAN connection to the IC. Voltage for the IC is provided by circuits CBP29 (WH/VT) and 1566 (RD/YE). Circuit GD111 (BK/BU) provides ground.

The IC shares the HS-CAN with the following modules

1. PCM
2. Steering effort control module (SECM)
3. ABS module
4. Restraints control module (RCM)
5. 4X4 control module
6. Accessory protocol interface module (APIM)

The IC shares the MS-CAN with the following modules

1. Audio control module (ACM)
2. Rear entertainment module (RETM)
3. Driver seat module (DSM)
4. HVAC module
5. Accessory protocol interface module (APIM)
6. Liftgate/trunk module (LTM)
7. Satellite digital audio receiver system (SDARS) module
8. Smart junction box (SJB)

This pinpoint test is intended to diagnose the following

1. Fuse(s)
2. Wiring, terminals or connectors
3. IC

The 4X4 control module communicates with the scan tool through the high speed controller area network (HS-CAN). Circuits VDB04 (WH/BU) (HS-CAN +) and VDB05 (WH) (HS-CAN -) provide the network connection to the 4X4 control module. The 4X4 control module shares the HS-CAN with the PCM, the accessory protocol interface module (APIM), the steering effort control module (SECM), the ABS module, the restraints control module (RCM), occupant classification system module (OCSM) and the instrument cluster (IC). Voltage for the 4X4 control module is provided by circuit CBP34 (VT/BN) and SBP11 (BU/RD). Ground is provided by circuit GD148 (BK/YE).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. 4X4 control module

The RCM communicates with the scan tool through the high speed controller area network (HS-CAN). Circuits VDB04 (WH/BU) (HS-CAN +) and VDB05 (WH) (HS-CAN -) provide the network connection to the RCM. The RCM shares the HS-CAN with the PCM, the accessory protocol interface module (APIM), the steering effort control module (SECM), the ABS module, the 4X4 control module, the occupant classification system module (OCSM) and the instrument cluster (IC). Voltage for the RCM is provided by circuit CBP32 (GN/VT), and the RCM is case grounded.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. Case ground open
4. RCM

The occupant classification system module (OCSM) communicates with the scan tool through the medium speed controller area network (MS-CAN). Circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the network connection to the OCSM. The OCSM shares the MS-CAN with the smart junction box (SJB), the accessory protocol interface module (APIM), the driver seat module (DSM), the HVAC module, the rear entertainment module (RETM), the satellite digital audio receiver system (SDARS) module, and the instrument cluster (IC). Voltage for the OCSM is provided by circuit CBP46 (WH/BU). Circuit GD133 (BK) provides ground.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. OCSM

The steering effort control module (SECM) communicates with the scan tool through the high speed controller area network (HS-CAN). Circuits VDB04 (WH/BU) (HS-CAN +) and VDB05 (WH) (HS-CAN -) provide the network connection to the steering effort control module (SECM). The steering effort control module (SECM) shares the HS-CAN with the PCM, the accessory protocol interface module (APIM), the ABS module, the restraints control module (RCM), the occupant classification system module (OCSM), the 4X4 control module and the instrument cluster (IC). Voltage for the steering effort control module (SECM) is provided by circuits SBP13 (GY/RD) and CBP35 (YE/GY) and circuit GD148 (BK/YE) provides ground.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. SECM

The smart junction box (SJB) communicates with the scan tool through the medium speed controller area network (MS-CAN). Circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the network connection to the SJB. The SJB shares the MS-CAN with the HVAC module, the accessory protocol interface module (APIM), the audio control module (ACM), the driver seat module (DSM), the rear entertainment module (RETM), the satellite digital audio receiver system (SDARS) module, the liftgate/trunk module (LTM) and the instrument cluster (IC). Voltage for the SJB is provided by redundant circuits. Fuse 5 (10A) provides voltage, and circuit GD133 (BK) provides ground.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. SJB

The audio control module (ACM) communicates with the scan tool through the medium speed controller area network (MS-CAN). Circuits VDB06 (GY/OG) (HS-CAN +) and VDB07 (VT/OG) (HS-CAN -) provide the network connection to the ACM. The ACM shares the MS-CAN with the HVAC module, the accessory protocol interface module (APIM), the smart junction box (SJB), the driver seat module (DSM), the rear entertainment module (RETM), the satellite digital audio receiver system (SDARS) module, the liftgate/trunk module (LTM) and the instrument cluster (IC). Voltage for the ACM is provided by circuit SPB39 (WH/RD) and circuit GD103 (BK/BU) provides ground.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. ACM

The driver seat module (DSM) communicates with the scan tool through the medium speed controller area network (MS-CAN). Circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the network connection to the DSM. The DSM shares the MS-CAN with the smart junction box (SJB), the accessory protocol interface module (APIM), the HVAC module, the audio control module (ACM), the liftgate/trunk module (LTM), the rear entertainment module (RETM), the satellite digital audio receiver system (SDARS) module, and the instrument cluster (IC). Voltage and ground for the DSM is provided by circuits SBB32 (VT/RD) and SBP12 (GN/RD). Circuits GD147 (BK/VT) provides ground.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. DSM

The rear entertainment module (RETM) communicates with the scan tool through the medium speed controller area network (MS-CAN). Circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the network connection to the RETM. The RETM is only on vehicles equipped with rear seat entertainment. The RETM shares the MS-CAN with the smart junction box (SJB), the accessory protocol interface module (APIM), the audio control module (ACM), the HVAC module, the driver seat module (DSM), the satellite digital audio receiver system (SDARS) module, the liftgate/trunk module (LTM), and the instrument cluster (IC). Voltage for the RETM is provided by circuit SBP03 (BU/RD). Ground is provided by circuit GD103 (BK/BU).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. RETM

The liftgate/trunk module (LTM) communicates with the scan tool through the medium speed controller area network (MS-CAN). Circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the network connection to the LTM. The LTM shares the MS-CAN with the smart junction box (SJB), the accessory protocol interface module (APIM), the audio control module (ACM), the HVAC module, the driver seat module (DSM), the rear entertainment module (RETM), the satellite digital audio receiver system (SDARS) module and the instrument cluster (IC). Voltage for the LTM is provided by circuits SBB29 (GY/RD) and SBP14 (BN/RD). Ground is provided by circuit GD147 (BK/VT).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. LTM

The satellite digital audio receiver system (SDARS) module communicates with the scan tool through the medium speed controller area network (MS-CAN). Circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the network connection to the SDARS module. The SDARS module shares the MS-CAN with the smart junction box (SJB), the accessory protocol interface module (APIM), the audio control module (ACM), the HVAC module, the driver seat module (DSM), the rear entertainment module (RETM), the liftgate/trunk module (LTM) and the IC. Voltage for the SDARS module is provided by circuit SBP03 (BU/RD). Ground is provided by circuit GD103 (BK/BU).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. SDARS module

The HVAC module communicates with the scan tool through the medium speed controller area network (MS-CAN). Circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the network connection to the HVAC module. The HVAC module shares the MS-CAN with the smart junction box (SJB), the ACM, the driver seat module (DSM), the rear entertainment module (RETM), the SDARS module, the liftgate/trunk module (LTM) and the instrument cluster (IC). Voltage for the HVAC module is provided by circuits CBP37 (WH) and SBP15 (WH/RD). Circuit GD111 (BK/BU) provides ground.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. HVAC module

The accessory protocol interface module (APIM) communicates with the scan tool through the high speed controller area network (HS-CAN). Circuits VDB04 (WH/BU) (HS-CAN +) and VDB05 (WH) (HS-CAN -) provide the HS-CAN connection to the APIM. Circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the MS-CAN connection to the APIM. Voltage for the APIM is provided by circuit SBP03 (BU/RD). Circuit GD103 (BK/BU) provides ground.

The APIM shares the HS-CAN with the following modules

1. PCM
2. Steering effort control module (SECM)
3. ABS module
4. Occupant classification system module (OCSM)
5. Restraints control module (RCM)
6. 4X4 control module
7. Instrument cluster (IC)

The APIM shares the MS-CAN with the following modules

1. Audio control module (ACM)
2. Rear entertainment module (RETM)
3. Driver seat module (DSM)
4. HVAC module
5. Instrument cluster (IC)
6. Liftgate/trunk module (LTM)
7. Satellite digital audio receiver system (SDARS) module
8. Smart junction box (SJB)

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. APIM

The parking air module (PAM) communicates with the scan tool through the International Standards Organization (ISO) 9141 communications network, circuit VDB10 (GY). Voltage for the PAM is provided by circuit CBP35 (YE/GY). Ground is provided by circuit GD147 (BK/YE) or GD148 (BK/YE).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. Parking aid module

The scan tool is connected to the data link connector (DLC) to communicate with the high speed controller area network (HS-CAN), medium speed controller area network (MS-CAN), and International Standards Organization (ISO) 9141 communication network. Voltage for the scan tool is provided by circuit SBP20 (GN/RD). Ground is provided by circuit GD111 (BK/BU).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. Scan tool

Scheme 2

1. Q1 CHECK DLC PINS FOR DAMAGE NOTE: Most faults are due to connector and/or wiring concerns. Carry out a thorough inspection and verification before proceeding with the Pinpoint Test. Disconnect the scan tool cable from the DLC. Inspect DLC pins 4, 5 and 16 for damage. Are DLC pins 4, 5 and 16 OK? YES : Go to Q2 . NO : REPAIR the DLC as necessary. CLEAR the DTCs. REPEAT the network test with the scan tool.
2. Q2 CHECK THE VOLTAGE SUPPLY CIRCUIT TO THE DLC Measure the voltage between the DLC C251-16, circuit SBP20 (GN/RD), harness side and ground. Is the voltage greater than 10 volts? YES : Go to Q3 . NO : VERIFY the smart junction box (SJB) fuse 20 (15A) is OK. If OK, REPAIR the circuit. REPEAT the network test with the scan tool.
3. Q3 CHECK THE DLC GROUND CIRCUITS FOR AN OPEN Measure the resistance between the DLC C251-4 and C251-5, circuits GD111 (BK/BU), harness side and ground. Are the resistances less than 5 ohms? YES : REPAIR the scan tool. REPEAT the network test with the scan tool. NO : REPAIR the circuit in question. REPEAT the network test with the scan tool.

An open circuit VDB04 (WH/BU) (HS-CAN +) or VDB05 (WH) (HS-CAN -) may cause intermittent or unreliable communication to all modules on the HS-CAN. The following modules communicate on the HS-CAN

1. PCM
2. Accessory protocol interface module (APIM)
3. Steering effort control module (SECM)
4. ABS module
5. Restraints control module (RCM)
6. 4X4 control module
7. Instrument cluster (IC)
8. Occupant classification system module (OCSM)

In the event that one of the 2 network circuits (HS-CAN + or HS-CAN -) becomes open to a module on the network, unreliable network communication to all modules on the network may result.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors

Circuits VDB04 (WH/BU) (HS-CAN +) and VDB05 (WH) (HS-CAN -) provide the HS-CAN connection. The HS-CAN is used for network communication between the PCM, the steering effort control module (SECM), the ABS module, the restraints control module (RCM), occupant classification system module (OCSM), the 4X4 control module, the accessory protocol interface module (APIM) and the instrument cluster (IC).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. ABS module
4. APIM
5. 4X4 control module
6. IC
7. OCSM
8. PCM
9. RCM
10. SECM

The MS-CAN uses an unshielded twisted pair cable, circuits VDB06 (GY/OG) and VDB07 (VT/OG). The following modules communicate on the MS-CAN

1. Audio control module (ACM)
2. Accessory protocol interface module (APIM)
3. Rear entertainment module (RETM)
4. Driver seat module (DSM)
5. HVAC module
6. Instrument cluster (IC)
7. Liftgate/trunk module (LTM)
8. Satellite digital audio receiver system (SDARS) module
9. Smart junction box (SJB)

In the event that one of the 2 network circuits (HS-CAN + or HS-CAN -) becomes open to a module on the network, unreliable network communication to all modules on the network may result.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors

The medium speed controller area network (MS-CAN) uses an unshielded twisted pair cable, circuits VDB06 (GY/OG) and VDB07 (VT/OG). The smart junction box (SJB), the HVAC module, the audio control module (ACM), the driver seat module (DSM), the rear entertainment module (RETM), the satellite digital audio receiver system (SDARS) module, the liftgate/trunk module (LTM), the accessory protocol interface module (APIM) and the instrument cluster (IC) all communicate on the MS-CAN.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. ACM
3. APIM
4. DSM
5. RETM
6. HVAC module
7. IC
8. LTM
9. SDARS module
10. SJB

See also:
• SUPPLEMENTAL RESTRAINT SYSTEM