Operation CHARM: Car repair manuals for everyone.
Home >> Fiat >> 2012 >> 500c L4-1.4L >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> Manufacturer Code Charts >> CAN C Bus No Response

CAN C Bus No Response






CAN C BUS NO RESPONSE





For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

The primary communication network between electronic control modules is the Controller Area Network (CAN) data bus system. The Controller Area Network (CAN) data bus allows all electronic modules connected to the bus to share information with each other. Regardless of whether a message originates from a module on the higher speed CAN C (500K) Bus or on the lower speed bus, CAN B (50K) Bus, the message structure and layout is similar, which allows the Body Control Module/Central GateWay (BCM or BCMCGW) to process and transfer messages between the CAN buses. The BCM stores Diagnostic Trouble Codes (DTCs) for certain bus network faults on the CAN C (500K) Bus and CAN B (50K) Bus.

All modules transmit and receive messages over one of these buses. Data exchange between the modules is achieved by serial transmission of encoded data messages (a form of transmission in which data bits are sent sequentially, one at a time, over a single line). Each module can both send and receive serial data simultaneously. Each data bit of a CAN Bus message is carried over the bus as a voltage differential between the two bus circuits which, when strung together, form a message. Each module uses arbitration to sort the message priority if two competing messages are attempting to be broadcast at the same time. Corruption of a single bit within a message will corrupt the entire message. Each message contains a Cyclic Redundancy Check (CRC) which specifies the message size exactly. If the message detected conflicts with the CRC the ECU receiving it will determine the message to be an error and consider that communication has not been possible. Diagnosis of this condition using a lab scope may reveal activity that appears to be Bus data messages even if no actual communication is possible. Communication problems that affect the whole bus, as a result of opens and terminal push outs are more likely to occur on data busses that operate at a high speed than a data bus that operates at a lower speed.

When an open circuit or terminal push out occurs one or more modules can become isolated from the remainder of the bus. The isolated module will attempt to communicate, but will not be able to receive messages or determine arbitration from other modules. Each time the isolated module attempts to communicate it alters the bus voltage on the intact bus circuit. Without functioning arbitration the isolated module alters the bus voltage while other bus messages are being sent thereby corrupting the messages on the remainder of the bus.

The CAN C bus modules are connected in series, and the CAN B bus modules are connected in parallel. Both use a two-wire bus using a twisted pair, where the wires are wrapped around each other to provide shielding from unwanted electromagnetic induction, thus preventing interference with the relatively low voltage signals being carried through them. While the CAN bus is operating (active), one of the bus wires will carry a higher voltage and is referred to as the CAN High or CAN bus (+) wire, while the other bus wire will carry a lower voltage and is referred to as the CAN Low or CAN bus (-) wire.






1.

NOTE: The CAN C bus modules are connected in series. The Data Link Connector (DLC) is connected to the bus through the Body Control Module (BCM). The termination resistors for the CAN C bus are located in the BCM and Powertrain Control Module (PCM). Normal bus resistance is approximately 60 Ohms when both the BCM and PCM are connected. The bus resistance is approximately 120 Ohms when only the BCM or PCM is connected.
CHECK THE CAN C BUS CIRCUITS FOR A SHORT TO VOLTAGE
1. Disconnect the scan tool.
2. Turn the ignition on.
3. Measure the voltage between ground and the CAN C Bus (+) circuit at the DLC.
4. Measure the voltage between ground and the CAN C Bus (-) circuit at the DLC.

Is either voltage above 10.0 volts?

Yes

- Go To 2

No

- Go To 3

2. CHECK THE CAN C BUS CIRCUITS FOR A SHORT TO VOLTAGE IN THE HARNESS FROM THE DLC TO BCM
1. Turn the ignition off.
2. Disconnect the BCM C3 harness connector.
3. Turn the ignition on.
4. Measure the voltage between ground and the CAN C Bus (+) circuit at the DLC.
5. Measure the voltage between ground and the CAN C Bus (-) circuit at the DLC.

Is any voltage present?

Yes

- Repair the short to voltage in the CAN C Bus circuit.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Diagnose the short to voltage in the CAN C Bus circuit. The concern is located in one of the CAN C Bus circuits or modules between the BCM and the PCM. Starting with the PCM and working towards the BCM, use the module connectors to isolate portions of the bus to assist in determining the location of the concern. Repair as necessary. Only replace a module after all harness concerns are diagnosed.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

3. CHECK THE CAN C BUS CIRCUITS FOR A SHORT TO GROUND
1. Turn the ignition off.
2. Disconnect and isolate the negative battery cable.
3. Measure the resistance between ground and the CAN C Bus (+) circuit at the DLC.
4. Measure the resistance between ground and the CAN C Bus (-) circuit at the DLC.

Are the resistances above 5.0 Ohms?

Yes

- Go To 5

No

- Go To 4

4. CHECK THE CAN C BUS CIRCUITS FOR A SHORT TO GROUND IN THE HARNESS FROM THE DLC TO BCM
1. Disconnect the BCM C3 harness connector.
2. Measure the resistance between ground and the CAN C Bus (+) circuit at the DLC.
3. Measure the resistance between ground and the CAN C Bus (-) circuit at the DLC.

Are the resistances above 10k Ohms?

Yes

- Diagnose the short to ground in the CAN C Bus circuit. The concern is located in one of the CAN C Bus circuits or modules between the BCM and the PCM. Starting with the PCM and working towards the BCM, use the module connectors to isolate portions of the bus to assist in determining the location of the concern. Repair as necessary. Only replace a module after all harness concerns are diagnosed.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Repair the short to ground in the CAN C Bus circuit.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

5. CHECK THE CAN C BUS CIRCUITS FOR A SHORT TOGETHER




1. Measure the resistance between the CAN C Bus (+) circuit and the CAN C Bus (-) circuit at the DLC.

Is the resistance below 5.0 Ohms?

Yes

- Go To 6

No

- Go To 7

6. CHECK THE CAN C BUS CIRCUITS FOR A SHORT TOGETHER IN THE HARNESS FROM THE DLC TO BCM




1. Disconnect the BCM C3 harness connector.
2. Measure the resistance between the CAN C Bus (+) circuit and the CAN C Bus (-) circuit at the DLC.

Is the resistance above 10k Ohms?

Yes

- Diagnose the short between the CAN C Bus (+) circuit and the CAN C Bus (-). The concern is located in one of the CAN C Bus circuits or modules between the BCM and the PCM. Starting with the PCM and working towards the BCM, use the module connectors to isolate portions of the bus to assist in determining the location of the concern. Repair as necessary. Only replace a module after all harness concerns are diagnosed.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Repair the short between the CAN C Bus (+) circuit and the CAN C Bus (-).
- Perform the BODY VERIFICATION TEST. Body Verification Test.

7. CHECK THE CAN C BUS CIRCUITS FOR AN OPEN IN THE HARNESS FROM THE DLC TO BCM
1. Disconnect the BCM C3 harness connector.
2. Measure the resistance of the CAN C Bus (+) circuit between the DLC and the BCM C3 harness connector.
3. Measure the resistance of the CAN C Bus (-) circuit between the DLC and the BCM C3 harness connector.

Are the resistances below 5.0 Ohms?

Yes

- Go To 8

No

- Repair the open in the CAN C Bus circuit.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

8. CHECK FOR CORRECT BUS TERMINATION RESISTANCE




1. Reconnect the BCM C3 harness connector.
2. Measure the resistance between the CAN C Bus (+) circuit and the CAN C Bus (-) at the DLC.

Is the resistance below 67 Ohms?

Yes

- Test complete, the condition or conditions that originally set this DTC are not present at this time. Using the wiring diagrams as a guide, check all related splices and connectors for signs of water intrusion, corrosion, pushed out or bent terminals, and correct pin tension.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- For a resistance measurement of approximately 120 Ohms, Go To 9
- For all others, repair the open or high resistance in the CAN C Bus (+) circuit or the CAN C Bus (-) circuit. The concern is located in one of the CAN C Bus circuits or modules between the BCM and the PCM. Starting with the PCM and working towards the BCM, use the module connectors to isolate portions of the bus to assist in determining the location of the concern. Repair as necessary. Only replace a module after all harness concerns are diagnosed.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

9. DETERMINE WHICH TERMINATION MODULE IS NOT CONNECTED TO THE CAN C BUS




1. Disconnect the PCM harness connectors.
2. Measure the resistance between the CAN C Bus (+) circuit and the CAN C Bus (-) at the DLC.

Is the resistance approximately 120 Ohms?

Yes

- The BCM is connected to the CAN C bus. The open is between the BCM and PCM. Use the module connectors to isolate portions of the bus to assist in determining the location of the concern. Repair as necessary. Only replace a module after all harness concerns are diagnosed.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Replace the BCM. Body Control Module - Removal.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

pro multis · About Operation CHARM