Scan Tool Does Not Communicate With Class 2 Serial Data Line

SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DATA LINE








CIRCUIT OPERATION
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.

The diagnostic procedure assumes that all modules are powered. When you are uncertain whether this condition is met, perform the Diagnostic System Check for the module in question. Diagnostic Trouble Codes (DTCs) 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
^ Use a J3561 6-A when probing or checking electrical connector terminals. The J3561 6-A prevents terminal damage, plus checks for proper terminal contact tension.
^ If a short to B+ is present a history U1301 will set in the modules. Refer to DTC U1301 Class 2 Short to Battery
^ If a short to ground is present a history U1300 will set in the modules. Refer to DTC U1300 Class 2 Short to Ground
^ If the malfunction is intermittent refer to Diagrams / Intermittents and Poor Connections Diagnosis.
^ Disconnecting modules and turning the ignition switch to ON may cause DTCs in these modules. Check for DTCs in each module upon completion of the required repair.

TEST DESCRIPTION
2. 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.
3. DTCs U1300 and/or U1301 may be retrieved with a history status. These DTCs are not the cause of the present condition.
4. A state of health DTC with a history status indicates the malfunction occurred when the ignition was on.
5. Data link connector terminals 2 and 5 provide the connection to the Class 2 serial data circuit and the signal ground circuit respectively.
7. The Class 2 serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wiring for a short, make sure there is not a module connected to the wire being tested.
8. Since the short is not in the wiring harness the malfunction is due to one of the modules.
13. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.
14. The communication malfunction may have prevented diagnosis of the customer complaint.