Module Communications Network: Overview Ford Focus II facelift

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

Vehicle communication utilizes both high speed (HS) and medium speed (MS) controller area network (CAN) communications. 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 individual control modules that control each function.

The vehicle has 2 module communication networks

1. High speed (HS) CAN
2. Medium speed (MS) CAN

Both 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 both networks from one connector. The DLC can be found under the instrument panel.

Scheme 1

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. ACM
2. APIM (if equipped)
3. FCIM
4. FDIM
5. HVAC module (if equipped)
6. IC
7. SDARS module (if equipped)
8. 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. PCM
2. ABS module
3. RCM
4. OCSM
5. IC
6. APIM (if equipped)

Principles of Operation

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

Vehicle communication utilizes both medium and high speed controller area network (CAN) communications. CAN is a method for transferring data among distributed electronic modules via a serial data bus.

The vehicle is equipped with 2 module communication networks

1. High speed (HS) CAN
2. Medium speed (MS) 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 ABS module (if equipped), the restraints control module (RCM), the occupant classification system module (OCSM), the accessory protocol interface module (APIM) and the instrument cluster (IC).

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. 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 instrument cluster (IC), the restraints control module (RCM), the accessory protocol interface module (APIM) and the occupant classification system module (OCSM). Voltage for the ABS module is provided by circuits SBB18 (YE/RD), SBB09 (RD) and CBP31 (BU/OG). Ground is provided by circuit GD122 (BK).

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). 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 medium speed controller area network (MS-CAN) connection to the IC. The IC shares the HS-CAN with the PCM, the ABS module, the restraints control module (RCM), the accessory protocol interface module (APIM) and the occupant classification system module (OCSM).

The IC shares the MS-CAN with the smart junction box (SJB), the HVAC module, the audio control module (ACM), the satellite digital audio receiver system (SDARS) module, the accessory protocol interface module (APIM), the front controls interface module (FCIM) and the front display interface module (FDIM). Voltage for the IC is provided by circuits CBP29 (WH/VT) and SBP26 (YE/RD). Circuits GD134 (BK/VT) and GD138 (BK/WH) provide ground.

This pinpoint test is intended to diagnose the following

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

The occupant classification system module (OCSM) 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 OCSM. The OCSM shares the HS-CAN with the PCM, the ABS module, the instrument cluster (IC), the accessory protocol interface module (APIM) and the restraints control module (RCM). Voltage for the OCSM is provided by circuit CBX02 (BN/RD). Circuit GD109 (BK) provides ground.

This pinpoint test is intended to diagnose the following

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

The restraints control module (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 HS-CAN connection to the RCM. The RCM shares the HS-CAN with the PCM, the ABS module, the instrument cluster (IC), the accessory protocol interface module (APIM) and the occupant classification system module (OCSM). Voltage for the RCM is provided by circuit CBP46 (WH/BU). The RCM is case grounded.

This pinpoint test is intended to diagnose the following

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

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 SBP13 (GY/RD) . Circuit GD114 (BK/BU) provides ground.

The APIM shares the HS-CAN with the PCM, the ABS module, the instrument cluster (IC), the occupant classification system module (OCSM) and the restraints control module (RCM).

The APIM shares the MS-CAN with the audio control module (ACM), the front controls interface module (FCIM), the front display interface module (FDIM), the satellite digital audio receiver system (SDARS) module, the HVAC module, the instrument cluster (IC) and the smart junction box (SJB).

This pinpoint test is intended to diagnose the following

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

The front controls interface module (FCIM) 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 FCIM. The FCIM shares the MS-CAN with the instrument cluster (IC), the smart junction box (SJB), the HVAC module, the audio control module (ACM), the accessory protocol interface module (APIM), the front display interface module (FDIM) and the satellite digital audio receiver system (SDARS) module. Voltage to the FCIM is provided by circuit SBP39 (WH/RD). Ground is provided by circuit GD110 (BK/VT).

This pinpoint test is intended to diagnose the following

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

The front display interface module (FDIM) 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 FDIM. The FDIM shares the MS-CAN with the instrument cluster (IC), the smart junction box (SJB), the HVAC module, the audio control module (ACM), the front controls interface module (FCIM) and the satellite digital audio receiver system (SDARS) module. Voltage to the front display interface module is provided by circuit SBP39 (WH/RD). Ground is provided by circuit GD134 (BK/VT).

This pinpoint test is intended to diagnose the following

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

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 instrument cluster (IC), the smart junction box (SJB), the HVAC module, the audio control module (ACM), the accessory protocol interface module (APIM), the front controls interface module (FCIM) and the front display interface module (FDIM). Voltage to the SDARS module is provided by circuit SBP03 (BU/RD). Ground is provided by circuit GD110 (BK/WH).

This pinpoint test is intended to diagnose the following

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

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. Voltage for the SJB is provided by SJB fuse 5 (10A). Circuit GD133 (BK) provides ground.

The SJB shares the MS-CAN with the instrument cluster (IC), the HVAC module, the audio control module (ACM), the front display interface module (FDIM), the front controls interface module (FCIM) and the satellite digital audio receiver system (SDARS) module (if equipped).

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) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the network connection to the ACM. The ACM shares the MS-CAN with the instrument cluster (IC), the smart junction box (SJB), the HVAC module, the satellite digital audio receiver system (SDARS) module, the accessory protocol interface module (APIM), the front controls interface module (FCIM) and the front display interface module (FDIM). Voltage for the ACM is provided by circuit SBP39 (WH/RD). Ground is provided by circuit GD114 (BK/BU).

This pinpoint test is intended to diagnose the following

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

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 instrument cluster (IC), the smart junction box (SJB), the audio control module (ACM), the satellite digital audio receiver system (SDARS) module, the accessory protocol interface module (APIM), the front controls interface module (FCIM) and the front display interface module (FDIM). Voltage to the HVAC module is provided by circuits SBP15 (WH/RD) and CBP37 (WH). Ground is provided by circuit GD138 (BK/WH).

This pinpoint test is intended to diagnose the following

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

The medium speed controller area network (MS-CAN) uses an unshielded twisted pair cable, circuits VDB06 (GY/OG) and VDB07 (VT/OG). The audio control module (ACM), the accessory protocol interface module (APIM), the front controls interface module (FCIM), the front display interface module (FDIM), the satellite digital audio receiver system (SDARS) module, the HVAC module, the smart junction box (SJB) and the instrument cluster (IC) all communicate on the MS-CAN.

In the event that 1 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 audio control module (ACM), the HVAC module, the accessory protocol interface module (APIM), the satellite digital audio receiver system (SDARS) module, the front display interface module (FDIM) and the front controls interface module (FCIM) communicate with the scan tool using the MS-CAN. The instrument cluster (IC), while on the MS-CAN, communicates with the scan tool only on the HS-CAN.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. IC
3. APIM
4. SJB
5. ACM
6. FCIM
7. HVAC module
8. SDARS module
9. FDIM

The high speed controller area network (HS-CAN) is used for communication between the PCM, the ABS module, the restraints control module (RCM), the occupant classification system module (OCSM), the accessory protocol interface module (APIM) and the instrument cluster (IC). 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.

In the event that either circuit VDB04 (WH/BU) (HS-CAN +) or VDB05 (WH) (HS-CAN -) becomes open to any 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 accessory protocol interface module (APIM), the ABS module, the restraints control module (RCM), the occupant classification system module (OCSM) 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. IC
6. OCSM
7. PCM
8. RCM

The scan tool is connected to the data link connector (DLC) to communicate with the high speed controller area network (HS-CAN) and medium speed controller area network (MS-CAN). Voltage for the scan tool is provided by circuit SBP20 (GN/RD). Ground is provided by circuit GD134 (BK/VT).

This pinpoint test is intended to diagnose the following

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

Scheme 2

Scheme 3

Scheme 4

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 the 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. REPEAT the network test with the scan tool.
2. Q2 CHECK THE VOLTAGE TO THE SCAN TOOL VOLTAGE SUPPLY CIRCUIT FOR AN OPEN 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, circuit GD134 (BK/VT), harness side and ground; and between the DLC C251-5, circuit GD134 (BK/VT), 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.