Circuit Description
The UART serial data link allows information to be exchanged from module to module as needed. This is done by the PCM, the PCM requests and sends all the information that is transmitted on the UART line. When a scan tool is connected to the UART line it takes over for the PCM and sends and requests the needed information.
Conditions for Setting the DTC
DTC C1275 can be set anytime the ignition is on and a message has not been received for 7 seconds.
Action Taken When the DTC Sets
| • | A DTC C1275 is stored |
| • | The TCS is disabled |
| • | The TRACTION OFF indicator is turned on |
| • | The ABS remains functional |
Conditions for Clearing the DTC
| • | The condition for the DTC is no longer present and the scan tool clear DTC function is used |
| • | 50 ignition cycles have passed with no DTCs detected |
Diagnostic Aids
| • | Thoroughly inspect the wiring and the connectors. Failure to carefully and fully inspect the wiring and the connectors can result in misdiagnosis. Misdiagnosis may cause replacement of parts without repairing the malfunction. |
| • | If an intermittent malfunction exists, refer to Intermittents and Poor Connections Diagnosis in Wiring Systems. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step checks for a short to ground.
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This step checks for an open in CKT 800.
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This step checks for a short to voltage.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Diagnostic System Check performed? | -- | Go to Diagnostic System Check | |
2 | Is DTC C1276 set as a current DTC? | -- | ||
3 | Check the following grounds, G101, and G106 making sure each ground is clean tight and free of damage. Refer to Wiring Repairs in Wiring Systems. Were any loose, damaged, or corroded grounds found? | -- | ||
4 | Repair the grounds as necessary. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Diagnostic System Check | -- |
Is the resistance equal to the specified value? | OL (infinite) | |||
6 | Repair CKT 800 for a short to ground. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Diagnostic System Check | -- |
Is the resistance less than the specified value? | 5 ohms | |||
8 | Repair the open in CKT 800. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Diagnostic System Check | -- |
9 | Using the J 39200 DMM, measure the resistance between the J 39700 terminal 30 and the PCM connector C1 terminal 15. Is the resistance less than the specified value? | 5 ohms | ||
10 | Repair the open in CKT 800. Refer to Wiring Repairs in Wiring Systems. Is the circuit repair complete? | -- | Go to Diagnostic System Check | -- |
Is the voltage within the specified range? | Battery voltage | |||
12 | Repair CKT 800 for a short to battery. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Diagnostic System Check | -- |
13 | Suspect the PCM. Refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 3.8L. Is the diagnosis complete? | -- | Go to Diagnostic System Check | -- |
