Module Communications Network: Overview Ford Mustang V facelift 2

Multiplexing is a method of sending 2 or more signals simultaneously over a single circuit. Multiplexing is used to allow 2 or more electronic modules (nodes) to communicate simultaneously over a twisted-wire pair [data (+) and data (-)] network. The information or messages that can be communicated on these wires consists of commands, status or data. The advantage of using multiplexing is to reduce the weight of the vehicle by reducing the number of redundant components and electrical wiring.

The vehicle has 2 module communication networks which are connected to the Data Link Connector (DLC), located under the instrument panel on the driver side

1. High Speed Controller Area Network (HS-CAN)
2. Medium Speed Controller Area Network (MS-CAN)

The HS-CAN and MS-CAN are defined by various ISO documents

1. ISO 11898 specifies the electrical, mechanical, and procedural interface for Controller Area Network (CAN) serial communication technology.
2. ISO 15765 specifies network-layer protocol and timing parameters for CAN-based systems.
3. ISO 14229 specifies a common set of unified diagnostics and changes the way PIDs, DTCs and active commands are processed and displayed on the scan tool.

Scheme 1

Principles of Operation

Both High Speed Controller Area Network (HS-CAN) and Medium Speed Controller Area Network (MS-CAN) use an unshielded twisted pair cable of data (+) and data (-) circuits. The HS-CAN operates at a maximum data transfer speed of 500 Kbps and designed for real-time information transfer and control. The MS-CAN operates at a maximum data transfer speed of 125 Kbps for bus messages and is designed for general information transfer.

Normal CAN Operation

The data (+) and data (-) circuits are each regulated to approximately 2.5 volts during neutral or rested network traffic. As messages are sent on the data (+) circuit, voltage is increased by approximately 1.0 volt. Inversely, the data (-) circuit is reduced by approximately 1.0 volt when a message is sent.

Successful communication of a message can usually be identified by the slight spike at the end of a message transmission. Any signals that are significantly different than the normal CAN waveform may cause network DTCs (U-codes) to set or may cause a complete network outage.

Scheme 2

In the event the data (+) and data (-) circuits become shorted together, the signal stays at base voltage (2.5V) continuously and all communication capabilities are lost.

Scheme 3

In the event the data (+) circuit becomes shorted to ground, both the data (+) and data (-) circuits are pulled low (0V) and all communication capabilities are lost.

Scheme 4

In the event the data (-) circuit becomes shorted to ground, the data (-) circuit is pulled low (0V) and the data (+) circuit reaches near-normal peak voltage (3.0V) during communication but falls to 0V instead of normal base voltage (2.5V). Communication may continue but at a degraded level.

Scheme 5

In the event the data (+) circuit becomes shorted to battery voltage, the data (+) circuit is pulled high (12V) and the data (-) circuit falls to abnormally high voltage (above 5V) during communication and reaches battery voltage (12V) for peak voltage. Communication may continue but at a degraded level.

Scheme 6

In the event the data (-) circuit becomes shorted to battery voltage, both the data (+) and data (-) circuits are pulled high (12V) and all communication capabilities are lost.

Scheme 7

Rhythmic oscillations, inductive spikes or random interference can disrupt the network communications. The corruption signal source may be outside electrical interference such as motors or solenoids or internal interference generated from a module on the network. In some cases, an open in either the data (+) or data (-) circuit to a network module may cause the module to emit interference on the one circuit which is still connected. The trace shown in illustration is an example of a "sawtooth" pattern transmitted from a module with one open network circuit.

Other corruptions may be present when a module is intermittently powered up and down. The module on power up may initiate communication out of sync with other modules on the network causing momentary communication outages.

Normal Operation

The PCM communicates with the scan tool through the High Speed Controller Area Network (HS-CAN).

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).

This pinpoint test is intended to diagnose the following

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

The Instrument Panel Cluster (IPC) communicates with the scan tool through the High Speed Controller Area Network (HS-CAN) and the Medium Speed Controller Area Network (MS-CAN).

This pinpoint test is intended to diagnose the following

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

The Restraints Control Module (RCM) communicates with the scan tool through the High Speed Controller Area Network (HS-CAN).

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 High Speed Controller Area Network (HS-CAN).

This pinpoint test is intended to diagnose the following

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

The Smart Junction Box (SJB) communicates with the scan tool through the Medium Speed Controller Area Network (MS-CAN).

This pinpoint test is intended to diagnose the following

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

The Body Control Module B (BCM-B) communicates with the scan tool through the Medium Speed Controller Area Network (MS-CAN).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. BCM-B

The HVAC module communicates with the scan tool through the Medium Speed Controller Area Network (MS-CAN).

This pinpoint test is intended to diagnose the following

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

The Audio Front Control Module (ACM) communicates with the scan tool through the Medium Speed Controller Area Network (MS-CAN).

This pinpoint test is intended to diagnose the following

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

The Front Controls Interface Module (FCIM) communicates with the scan tool through the Medium Speed Controller Area Network (MS-CAN).

This pinpoint test is intended to diagnose the following

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

The Front Display Interface Module (FDIM) (without navigation) communicates with the scan tool through the Medium Speed Controller Area Network (MS-CAN).

This pinpoint test is intended to diagnose the following

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

The Global Positioning System Module (GPSM) communicates with the scan tool through the Medium Speed Controller Area Network (MS-CAN).

This pinpoint test is intended to diagnose the following

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

The Accessory Protocol Interface Module (APIM) communicates with the scan tool and other modules through the Medium Speed Controller Area Network (MS-CAN) and also communicates with other modules on the High Speed Controller Area Network (HS-CAN).

This pinpoint test is intended to diagnose the following

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

The Power Steering Control Module (PSCM) communicates with the scan tool and other modules through the High Speed Controller Area Network (HS-CAN).

This pinpoint test is intended to diagnose the following

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

The Parking Aid Module (PAM) communicates with the scan tool and other modules through the High Speed Controller Area Network (HS-CAN).

This pinpoint test is intended to diagnose the following

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

The VDM communicates with the scan tool through the High Speed Controller Area Network (HS-CAN).

This pinpoint test is intended to diagnose the following

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

The Medium Speed Controller Area Network (MS-CAN) uses an unshielded twisted pair cable, circuits VDB06 (MS-CAN -) and VDB07 (MS-CAN +).

Note. The Instrument Panel Cluster (IPC), while on the MS-CAN, communicates with the scan tool only on the High Speed Controller Area Network (HS-CAN).

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Audio Front Control Module (ACM)
3. Accessory Protocol Interface Module (APIM) (if equipped)
4. Body Control Module B (BCM-B)
5. Front Controls Interface Module (FCIM)
6. Front Display Interface Module (FDIM) (without navigation)
7. Global Positioning System Module (GPSM)
8. HVAC module
9. Instrument Panel Cluster (IPC)
10. Smart Junction Box (SJB)

The High Speed Controller Area Network (HS-CAN) uses an unshielded twisted pair cable, circuits VDB04 (HS-CAN +) and VDB05 (HS-CAN -).

Note. The APIM, while on the HS-CAN, communicates with the scan tool only on the Medium Speed Controller Area Network (MS-CAN).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. ABS module
4. Accessory Protocol Interface Module (APIM) (if equipped)
5. Engine temperature gauge (if equipped)
6. Instrument Panel Cluster (IPC)
7. Occupant Classification System Module (OCSM)
8. Parking Aid Module (PAM)
9. PCM
10. Power Steering Control Module (PSCM)
11. Restraints Control Module (RCM)
12. Vehicle Dynamics Module (VDM) (GT500)

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).

A loss of ground or poor ground at the DLC may result in HS-CAN or MS-CAN faults while the scan tool is connected. This may cause multiple malfunction indicators to be on with the scan tool connected to the DLC.

This pinpoint test is intended to diagnose the following

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