For 1990-2009 cars

### Circuit Description

Contemporary Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes. Diagnostic trouble codes DTC may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.

### Diagnostic Aids

The engine will not start when there is a total malfunction of the class 2 serial data circuit while the engine is not running.

The class 2 serial data circuit for the IPC and PCM are on a common terminal on the FUSE BLOCK-LEFT I/P connector .

The class 2 serial data circuit for the EBCM and SDM are on a common terminal on the FUSE BLOCK-LEFT I/P connector .

The class 2 serial data circuit for the DLC and BCM are on a common terminal on the FUSE BLOCK-LEFT I/P connector .

The class 2 serial data circuit for the VTD and IRC are on a common terminal on the FUSE BLOCK-LEFT I/P connector .

### test Description

1. A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit.

2. DTCs U1300 and/or U1301 may be retrieved with a history status. These DTCs are not the cause of the present condition.

3. A state of health DTC with a history status may be present along with a U1000 having a current status. This indicates the malfunction occurred when the ignition was on.

4. Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal battery negative circuit respectively.

5. An open in the class 2 serial data circuit between the DLC and the Fuse Block-Left I/P connector will prevent the scan tool from communicating with any module. This condition may not set a DTC.

6. A poor connection, short to battery negative or battery positive would cause this condition but may not set a DTC. Because the DLC and BCM share the same terminal at FUSE BLOCK-LEFT I/P the BCM must be taken out of the class 2 serial data circuit.

7. This test isolates the PCM from the class 2 serial data circuit.

8. This test isolates the IRC from the class 2 serial data circuit.

9. This test isolates the BCM from the class 2 serial data circuit.

10. This test isolates the IPC from the class 2 serial data circuit.

11. This test isolates the EBCM from the class 2 serial data circuit.

12. This test isolates the VTD from the class 2 serial data circuit.

13. This test isolates the SDM from the class 2 serial data circuit.

14. This test checks for a wiring problem.

15. This test checks for a wiring problem.

16. This test checks for a wiring problem.

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

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

Step | Action | Yes | No
--- | --- | --- | ---
1 | Install a scan tool. Does the scan tool power up? | Go to Step 2 | Go to Scan Tool Does Not Power Up
2 |

1. Turn on the ignition with the engine off.
2. Attempt to communicate with each module on the Class 2 serial data circuit. If using a Tech 2, obtain this information using the Class 2 Message Monitor feature.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 3

Go to Step 7

3 |

1. Select the display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
2. Record all of the displayed DTCs, the DTC status and the module which set the DTC.

Did you record any DTCs in the range of U1000 to U1255?

Go to Step 4

Go to Testing for Intermittent Conditions and Poor Connections

4 | Are the DTCs U1300, U1301 or U1305 retrieved from any module? | Go to Step 5 | Go to Step 6
5 | 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 in Wiring Systems:

• | Testing for Intermittent Conditions and Poor Connections

• | Circuit Testing

• | Connector Repairs

• | Wiring Repairs

Did you find and correct the condition?

Go to Step 22

Go to Step 6

6 | Are U1000 or U1255 the only DTC displayed in the previously specified range? | Go to DTC U1000 and U1255 | Go to Diagnostic Trouble Code (DTC) List
7 |

1. Turn off the ignition.
2. Disconnect the scan tool from the data link connector DLC.
3. Inspect for poor connections/terminal tension at the DLC terminals 2 and 5. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 22

Go to Step 8

8 | Test the DLC battery negative circuit terminal 5 for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 22 | Go to Step 9
9 | Inspect Fuse Block-Left I/P at the terminals containing the class 2 serial data circuit for poor connections / terminal tension. Refer to Wiring Repairs for the proper procedure. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.

Did you find and correct the condition?

Go to Step 22

Go to Step 10

10 |

1. Disconnect the Fuse Block-Left/IP connector containing the class 2 serial data circuits. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
2. Disconnect the connector that contains the class 2 serial data circuit, from the BCM. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
3. Test for a high resistance, short to battery positive voltage or ground between the Fuse Block-Left/IP class 2 serial data circuit terminal and the DLC connector terminal 2. Refer to Circuit Testing and Wiring Repairs for the proper procedure. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
4. Test for a short to battery positive voltage or ground from the Fuse Block-Left I/P terminal containing the class 2 serial data circuit and the BCM class 2 serial data circuit terminal . Refer to Circuit Testing and Wiring Repairs for the proper procedure. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
5. Test for a high resistance, short to battery positive voltage or ground between the class 2 serial data circuit terminals on the Fuse Block-Left I/P Refer to Circuit Testing , Wiring Repairs and Connector Repairs for the proper procedure. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
6. If a short is discovered in these tests the BCM and DLC mutual circuits will have to be separated at the FUSE BLOCK-LEFT I/P to isolate the lines from each other and items 3 and 4 must be rerun to determine in witch discreate circuit the malfunction is present. Refer to Connector Repairs for the proper procedure.

Did you find and correct the condition?

Go to Step 22

Go to Step 11

11 |

1. Connect the connector to the Fuse Block-Left I/P that contains the class 2 serial data circuit. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
2. Connect the connector containing the class 2 serial data circuit to the BCM. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
3. Disconnect the connector containing the class 2 serial data circuit from the PCM.
4. Install a scan tool.
5. Turn the ignition on with the engine off.
6. Attempt to communicate with any module on the class 2 serial data circuit.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 21

Go to Step 12

12 |

1. Turn off the ignition.
2. Disconnect the connector containing the class 2 serial data circuit from the IRC Radio . Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
3. Turn the ignition on with the engine off.
4. Attempt to communicate with any module on the class 2 serial data circuit.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 21

Go to Step 13

13 |

1. Turn off the ignition.
2. Disconnect the connector containing the class 2 serial data circuit from the BCM. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
3. Turn the ignition on with the engine off.
4. Attempt to communicate with any module on the class 2 serial data circuit.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 21

Go to Step 14

14 |

1. Turn off the ignition.
2. Disconnect the connector containing the class 2 serial data circuit from the IPC. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
3. Turn the ignition on with the engine off.
4. Attempt to communicate with any module on the class 2 serial data circuit.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 21

Go to Step 15

15 |

1. Turn off the ignition.
2. Disconnect the connector from the EBCM. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
3. Turn the ignition on with the engine off.
4. Attempt to communicate with any module on the class 2 serial data circuit. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 21

Go to Step 16

16 |

1. Turn off the ignition.
2. Disconnect the connector from the VTD. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
3. Turn the ignition on with the engine off.
4. Attempt to communicate with any module on the class 2 serial data circuit. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 21

Go to Step 17

17 |

1. Turn off the ignition.
2. Connect the connector containing the class 2 serial data circuit to the EBCM. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
3. Disconnect the connector containing the class 2 serial data circuit from the SDM. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
4. Turn the ignition on with the engine off.
5. Attempt to communicate with any module on the class 2 serial data circuit. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 21

Go to Step 18

18 |

1. Disconnect the connector containing the class 2 serial data circuit from the EBCM. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
2. Disconnect the connector containing the class 2 serial data circuit at Fuse Block-Left I/P. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
3. Test the connector containing the class 2 serial data circuit for a short to battery positive voltage or ground from the FUSE BLOCK-LEFT I/P and the EBCM connector containing the class 2 serial data circuit. Refer to Circuit Testing and Wiring Repairs for the proper procedure. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
4. Test the connector containing the class 2 serial data circuit for a short to battery positive voltage or ground from the FUSE BLOCK-LEFT I/P and the SDM connector containing the class 2 serial data circuit. Refer to Circuit Testing and Wiring Repairs for the proper procedure. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
5. If a short is discovered in item 3 or 4, the two mutual circuits will have to be separated at the FUSE BLOCK-LEFT I/P connector to isolate the lines from each other and items 3 and 4 must be rerun to determine in witch discreate circuit the malfunction is present. Refer to Connector Repairs for the proper procedure.

Did you Find and correct the condition?

Go to Step 22

Go to Step 19

19 |

1. Test for a short to battery positive voltage or ground from the FUSE BLOCK-LEFT I/P and the IPC connectors containing the class 2 serial data circuit. Refer to Circuit Testing and Wiring Repairs for the proper procedure. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's.
2. Test for a short to battery positive voltage or ground from the FUSE BLOCK-LEFT I/P and the PCM connectors containing the class 2 serial data circuit. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's Note LD9 or LA1 Engine . Refer to Circuit Testing and Wiring Repairs for the proper procedure.
3. If a short is discovered in the first two items, the two mutual circuits will have to be separated at the FUSE BLOCK-LEFT I/P connector to isolate the lines from each other and items 1 and 2 must be rerun to determine in witch discreate circuit the malfunction is present. Refer to Connector Repairs for the proper procedure.

Did you Find and correct the condition?

Go to Step 22

Go to Step 20

20 |

1. Test for a short to battery positive voltage or ground from the FUSE BLOCK-LEFT I/P and the IRC connector containing the class 2 serial data circuit. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's. Refer to Circuit Testing and Wiring Repairs for the proper procedure.
2. Test for a short to battery positive voltage or ground from the FUSE BLOCK-LEFT I/P and the VTD connector containing the class 2 serial data circuit. Refer to Data Link Connector Schematics for the appropriate circuit and connector ID's. Refer to Circuit Testing and Wiring Repairs for the proper procedure.
3. If a short is discovered in the first two items, the two mutual circuits will have to be separated at the FUSE BLOCK-LEFT I/P connector to isolate the lines from each other and items 1 and 2 must be rerun to determine in witch discreate circuit the malfunction is present. Refer to Connector Repairs for the proper procedure.

Did you Find and correct the condition?

Go to Step 22

Go to Step 7

21 | Replace the last module which was disconnected. Refer to Control Module References for the appropriate repair instructions for module replacement. Did you complete the replacement? | Go to Step 22 | --
22 |

1. Connect all of the disconnected modules.
2. Connect any other disconnected connectors.
3. Install a scan tool.
4. Turn on the ignition with the engine off.
5. Wait for 10 seconds. The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn off or disconnect the scan tool prior to performing this test.
6. Attempt to communicate with each module on the class 2 serial data circuit.

Does the scan tool communicate with each module on the class 2 serial data circuit?

Go to Step 23

Go to Step 7

23 |

1. Select the display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.
2. Record all of the displayed DTCs and the DTC status.

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

Go to Step 25

Go to Step 24

24 | Did you record any DTCs which do not begin with a "U"? | Go to Step 25 | Go to Step 27
25 | Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Did you complete the action? | Go to Step 26 | --
26 | Did you diagnose all of the DTCs? | Go to Step 27 | Go to Step 25
27 | Clear the DTCs using the scan tool. Did you complete the action? | System OK | --