Circuit Description
The Class II Serial Data Circuit is used to communicate between systems. Each system connected to the Class II Serial Data line 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 bus every two seconds. If a module is monitoring Node Alive messages for that module, it will reset its 5 second time for that particular 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 VTD 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 VTD learns the VCM ID, monitors for Node Alive messages from the VCM ID, and responds with a Vehicle Security Status acknowledge message. This tells the VCM, I heard you so you can stop sending the message.
Lost Communications DTCs (U-Codes) are equal to U1000 plus the ID. This is U1016 and U1192 for VTD.
Conditions for Setting the DTC
| • | The VCM has established communications, received the Vehicle Security Password during this ignition cycle for the established communications, and received Node Alive/SOH messages during this ignition cycle with the Vehicle Immobilizer Module (VIM). |
| • | The VCM has not detected communications, no Node Alive/SOH messages received from the VIM for 5 seconds. |
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:
| • | The vehicle starts |
| • | 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. The difference is that the Fail Enable Active bit in the Vehicle Security Status message will now be false while the Fuel Continue State bit will be true. |
| • | A DTC U1193 is stored in the VCM memory |
| • | The VCM will not illuminate the MIL |
When the failure occurs during with the ignition OFF, or before the VCM received a valid Passlock password during engine cranking:
| • | The vehicle does not start or it starts and stalls |
| • | 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. |
| • | A DTC U1193 is stored in the VCM memory |
| • | The VCM will not illuminate the MIL |
Conditions for Clearing the MIL/DTC
| • | This DTC requires an ignition cycle in order to change from Current to History |
| • | The VCM established communication with the VIM |
| • | 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 malfunction. |
| • | 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 |
| • | If the Class II Serial Data line is shorted to ground or shorted to voltage, all the modules or systems connected to the Class II Serial Data line will not be able to communicate properly. These systems or modules are capable of storing loss of communications DTCs (DTCs with the letter U as a prefix) in their memory. If a DTC U1193 is stored in the VCM memory, check for the same DTC stored in the Active Transfer Case (ATC) Control Module. The ATC Control Module also monitors the Node Alive/SOH message from the VIM. If the ATC Control Module has a DTC U1193 stored, check the VIM for an intermittent malfunction. If the ATC Control Module does not have a DTC U1193 stored, check for an open in the Class II Serial Data circuit between the VCM and the VIM. The VCM must also be checked for intermittent operation due to a loss of power or ground to the VCM itself. After repairing the cause of a DTC U1193, clear all DTCs from all systems capable of storing this DTC. |
| • | The scan tools Diagnostic Circuit Check can be used to: |
| - | Monitor the Class II Serial Data circuit for modules which have been or are communicating |
| - | Monitor for the presence of 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 tools Diagnostic Circuit Check 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. If a module is not listed at all, the module never successfully established communications with the scan tool. Refer to Diagnostic System Check - Data Link Communications for the complete Class II 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 communications can be established between the scan tool and the VIM. If the scan tool cannot communicate with the VIM, refer to Diagnostic System Check - Theft Deterrent
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This test determines if DTC U1193 is set due to a loss of communications with the VCM or the VIM. The ATC Control Module also communicates with the VIM. If a DTC U1193 is stored in the ATC Control Module memory, the VIM must be diagnosed first.
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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 line.
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Use a scan tool to clear and check for any DTCs in all the modules connected to the Class II Serial Data circuit (VCM, VIM, ATC, and EBCM).
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 |
Important: Use the scan tool to store the failed DTC information. This information will be erased when the Clear DTC function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||
Does the scan tool communicate with the VIM? | -- | |||||||||||
Is DTC U1193 stored in the ATC memory? | -- | |||||||||||
Check the Class II Serial Data circuit for the following intermittent conditions:
Was a problem found? | -- | |||||||||||
5 |
Does DTC U1193 reset? | -- | ||||||||||
6 | Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
7 | This DTC is intermittent. Are there any other DTCs that have not been diagnosed? | -- | Go to applicable DTC table | Go to Diagnostic Aids | ||||||||
8 |
Is the action complete? | -- | -- | |||||||||
Are any new DTCs displayed? | -- | System OK |
