For 1990-2009 cars

### Circuit Description

The powertrain control module (PCM) on this vehicle uses the class 2 serial data buss strictly for diagnostic purposes. When the PCM detects one of the following conditions on the class 2 serial data circuit for approximately 3 seconds, the setting of all other class 2 serial communication DTCs is inhibited and a DTC will set.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

• | DTC U1300 Class 2 Data Link Low

• | DTC U1301 Class 2 Data Link High

• | DTC U1305 Class 2 Data Link Low or High

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .

DTC Symptom | DTC Symptom Descriptor
--- | ---
00 | No Additional Information

### Conditions for Running the DTCs

• | Voltage supplied to the module is in the normal operating voltage range.

• | The vehicle power mode requires serial data communication to occur.

### Conditions for Setting the DTCs

• | No valid messages are detected on the class 2 serial data circuit.

• | The voltage level detected on the class 2 serial data circuit is in one of the following conditions:

- | High

- | Low

• | The above conditions are met for approximately 3 seconds.

### Action Taken When the DTCs Sets

The module uses default values for all parameters received on the class 2 serial data circuit.

### Conditions for Clearing the DTC

• | A current DTC clears when the malfunction is no longer present.

• | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. If you can communicate with the PCM, the malfunction may be an intermittent short to voltage or ground in the wiring of the class 2 serial data circuit.

2. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.

3. The communication malfunction may have prevented diagnosis of the customer complaint.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Data Communication Schematics Connector End View Reference: Master Electrical Component List
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Turn ON the ignition, with the engine OFF.
2. Using a scan tool, attempt to communicate with the powertrain control module (PCM).

Can you communicate with the PCM?

Go to Step 4

Go to Scan Tool Does Not Communicate with Class 2 Device

3 | Important: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions. Test the class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following:

• | Testing for Intermittent Conditions and Poor Connections

• | Circuit Testing

• | Connector Repairs

• | Wiring Repairs

Did you find and correct the condition?

Go to Step 5

Go to Step 4

4 | Important: Perform the module setup procedure, if required. Replace the PCM. Refer to Control Module References for the appropriate repair instructions. Did you complete the replacement? | Go to Step 5 | --
5 |

1. Reconnect all of the disconnected modules.
2. Reconnect any other disconnected connectors.
3. Install a scan tool.
4. Turn ON the ignition, with the engine OFF.
5. Retrieve DTCs using the Vehicle DTC Information feature on the scan tool, under the Computer/Integrating System menu.

Did you record any DTCs which begin with a "U" and with a current status?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 6

6 | Did you record any DTCs which do not begin with a "U"? | Go to Diagnostic Trouble Code (DTC) List - Vehicle | Go to Step 7
7 | Did you diagnose all of the DTCs? | Go to Step 8 | Go to Step 5
8 | Use the scan tool in order to clear the DTCs. Did you complete the action? | System OK | --