For 1990-2009 cars
ABS Components
Cell 44: ABS/TCS Switch, UART, PCM, and Traction Control Switch
Handling ESD Sensitive Parts Notice
Cell 50: UART Serial Data Line

### 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.

1. This step checks for a short to ground.

2. This step checks for an open in CKT 800.

3. This step checks for a short to voltage.

#### DTC C1275 PCM Serial Data Malfunction

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Diagnostic System Check performed? | -- | Go to Step 2 | Go to Diagnostic System Check
2 | Is DTC C1276 set as a current DTC? | -- | Go to DTC C1276 Delivered Torque Signal Circuit Malfunction | Go to Step 3
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? | -- | Go to Step 4 | Go to Step 5
4 | Repair the grounds as necessary. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Diagnostic System Check | --
5 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the EBCM/EBTCM connector.
3. Install the J 39700 universal pinout box using the J 39700-25 cable adapter to the EBCM/EBTCM harness connector only.
4. Turn the ignition switch to the RUN position with the engine OFF.
5. Using the J 39200 DMM, measure the resistance between the J 39700 terminals 15 and B.

Is the resistance equal to the specified value?

OL (infinite)

Go to Step 7

Go to Step 6

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 | --
7 |

1. Disconnect the PCM connector C1.
2. Using the J 39200 DMM, measure the resistance between the J 39700 terminal 15 and the PCM connector C1 terminal 15.

Is the resistance less than the specified value?

5 ohms

Go to Step 9

Go to Step 8

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 | Go to Step 11 | Go to Step 10
10 | Repair the open in CKT 800. Refer to Wiring Repairs in Wiring Systems. Is the circuit repair complete? | -- | Go to Diagnostic System Check | --
11 |

1. Turn the ignition switch to the RUN position, engine off.
2. Using the J 39200 DMM, measure the voltage at terminal 15 of the J 39700 .

Is the voltage within the specified range?

Battery voltage

Go to Step 12

Go Step 13

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 | --