Circuit Description
The Class 2 Serial Data Circuit is used to communicate between systems. Each system connected to the Class 2 Serial Data circuit is assigned its own recognition code (ID/address). This code is used to identify which module or systems are communicating. The Node Alive or State of Health (SOH) messages are broadcast on the serial data circuit every two seconds. If the VCM is monitoring Node Alive messages, it will reset its 5 second timer when it receives the message from the Vehicle Immobilizer Module (VIM) module. Any system that cannot communicate properly will also store the appropriate communication DTCs that are assigned to the system(s) it could not communicate with.
The VIM sends a Vehicle Security Password when its ignition 1 input becomes active and includes its source ID. The Vehicle Security Password includes either a Fuel Continue Password or a Fuel Disable Password. The VCM learns the source ID, Monitors for the Node Alive messages, and responds with a Vehicle Security Status message including its VCM ID. The VIM learns the VCM ID, monitors for Node Alive messages from the VCM, and responds with a Vehicle Security Status acknowledge message. This informs the VCM that the message was received and it can stop sending it.
Lost Communications DTCs (U-Codes) are equal to U1000 plus the ID. This is U1193 for VIM.
Conditions for Running the DTC
The VCM has established communications, received the Vehicle Security Password and received Node Alive/SOH messages from the Vehicle Immobilizer Module (VIM).
Conditions for Setting the DTC
During the same ignition cycle, the VCM has lost communications and/or has not received Node Alive/SOH messages received from the VIM for 5 continuous seconds after it had been previously established.
Action Taken When the DTC Sets
When a failure occurs after the VCM enables fuel due to a receipt of a Vehicle Security Password containing the Fuel Continue Password:
| • | A DTC U1193 is stored in the VCM memory |
| • | The vehicle starts |
| • | The VCM will not illuminate the MIL |
| • | The VCM continues to enable fuel delivery (Fuel Enabled after Security Fault mode), until the fault is corrected and a valid password is received from the VIM. If the fault is corrected and a valid password is received, fuel delivery is enabled. |
When the failure occurs with the ignition OFF, or before the VCM received a valid Passlock password during engine cranking:
| • | A DTC P1626 is stored in the VCM memory |
| • | The vehicle does not start or it starts and stalls |
| • | The VCM will not illuminate the MIL |
| • | The VCM disables fuel delivery until the fault is corrected and a valid password is received from the VIM. Fuel delivery is disabled for the current ignition cycle. |
Conditions for Clearing the MIL/DTC
| • | A history DTC will clear after 40 consecutive ignition cycles if the condition for the malfunction is no longer present |
| • | The DTCs can be cleared using a scan tool |
Diagnostic Aids
Important: Do not clear the DTCs unless directed by a diagnostic procedure. Clearing the DTCs will also clear valuable Freeze Frame and Failure Records information.
| • | Check for published service bulletins relating to the exhibited symptoms or component operation. |
| • | Inspect all related wiring and connections, including the connections at the VCM and the VIM. These connections may cause an intermittent loss of communication. |
| • | Thoroughly check any circuit that can cause an intermittent complaint for the listed items: |
| - | Backed out terminals |
| - | Improper mating of connectors |
| - | Broken connector locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wiring connections |
| - | Physical damage to the wiring harness |
| - | Corroded terminals or connections |
| - | Moisture in the connector |
| • | If the Class 2 Serial Data circuit is shorted to ground or shorted to voltage, all the modules or systems connected to the Class 2 Serial Data circuit will not be able to communicate properly. The systems or modules that are capable of storing loss of communication DTCs (DTCs with the letter U as a prefix) will have these codes in their memory. If multiple history U codes are stored in all the modules, the likely cause is a fault in the Class 2 circuit. If the same U code appears in all the modules, then the module identified by the code may not be able to communicate or has an open in the Class 2 circuit leading to the module. If one module has multiple history U codes, that module may not be able to communicate intermittently. The VIM must also be checked for intermittent operation due to a loss of power or ground to the VIM itself. After repairing the cause of a DTC U1193, clear all DTCs from the systems capable of storing this DTC. |
| • | The scan tool's Diagnostic Circuit Check can be used to: |
| - | Monitor the Class 2 Serial Data circuit for modules that are or have been communicating |
| - | Monitor for loss of communications DTCs (DTCs with the letter U as a prefix U1001-U1199) |
| - | Clear the loss of communication DTCs. When a Clear Codes command is issued, all codes, Freeze Frame, and Failure Records information is cleared. |
| • | The scan tool's Class 2 Message Monitor will show the status of each module on the Class 2 circuit. A status of Active indicates that the module is communicating with the scan tool. An Inactive status indicates that the module previously communicated with the scan tool, but is not communicating currently. The inactive status will only appear if the loss of communication occurs while on the Message Monitor screen. If a module is not listed at all, the module never successfully established communications with the scan tool or lost communication while on another screen. Refer to Diagnostic System Check - Data Link Communications in Wiring Systems for the complete Class 2 data link to determine if there are any unlisted modules. |
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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This test checks if communication can be established between the scan tool and the VIM. If the scan tool cannot communicate with the VIM, refer to A Diagnostic System Check - Theft Deterrent in Theft Deterrent.
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This test checks for any opens in the serial data circuit between the VCM and the VIM. It also checks for any intermittent malfunctions associated with the serial data circuit.
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Use a scan tool to clear and check for any DTCs in all the modules connected to the Class 2 Serial Data circuit (VCM, VIM, ATC, and EBCM).
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear DTC Information function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||
Does the scan tool communicate with the VIM? | -- | Go to Diagnostic System Check - Theft Deterrent in Theft Deterrent | ||||||||||
Check the Class 2 Serial Data circuit for the following intermittent conditions:
Did you find a problem? | -- | |||||||||||
4 |
Does DTC U1193 reset? | -- | Go to Diagnostic System Check - Theft Deterrent in Theft Deterrent | |||||||||
5 | This DTC is intermittent. Are there any additional DTCs stored? | -- | Go to the applicable DTC table | Go to Diagnostic Aids | ||||||||
6 | Repair the circuit as necessary. Refer to Wiring Repairs or Connector Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
Are any new DTCs displayed? | -- | System OK |
