Scan Tool Does Not Communicate with Class 2 Device (With Immobilizer)

SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE (WITH IMMOBILIZER)

CIRCUIT DESCRIPTION
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 data link connector (DLC) allows communication with the modules for diagnostic purposes. 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
- The body control module (BCM) detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must be connected to the DLC for any other module to communicate with the scan tool.
- When the class 2 serial data circuit is shorted to ground or to voltage, the following DTCs may set:
- U1300
- U1301
- U1305

TEST DESCRIPTION

Step 1 - Step 10:

Step 11 - Step 17:

Step 18 - Step 24:

Step 25 - Step 29:

The numbers below refer to the step numbers on the diagnostic table.
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. The following modules communicate on class 2 serial data bus:
- The body control module (BCM)
- The communication interface module (OnStar(R)), w/UE1
- The digital radio receiver (DRR), w/U2K
- The driver door module (DDM)
- The driver seat module (DSM), w/AAB
- The DVD player
- The electronic brake control module (EBCM)
- The endgate module (EGM), for XUV
- The HVAC control module
- The HVAC control module - rear auxiliary
- The inflatable restraint sensing and diagnostic module (SDM)
- The instrument panel cluster (IPC)
- The liftgate control module (LGM), except XUV
- The passenger door module (PDM)
- The power roof module (PRM), for XUV
- The powertrain control module (PCM)
- The radio
- The transfer case shift control module (TCSCM), w/4WD
- The theft deterrent control module (VTD)
3. The following DTCs may be retrieved with a history status, but are not the cause of the present condition.
- U1300
- U1301
- U1305
6. A state of health (SOH) DTC with a history status may be present along with a U1000 code having a current status. This indicates that the malfunction occurred when the ignition was ON.
7. Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
10. A poor connection at the DLC terminal of the splice pack SP205 would cause this condition but will not set a DTC.
11. This step may eliminate the loop created by the PCM and VTD from failure cause.
12. An open in the class 2 serial data circuit between the DLC and splice pack SP205 will prevent the scan tool from communicating with any module. This condition will not set a DTC.
14. 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 wire for a short, make sure there is not a module connected to the wire being tested. This test isolates the BCM class 2 serial data circuits.
16. This test isolates the PCM class 2 serial data circuits.
18. The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must remain connected to the DLC for any other module to communicate with the scan tool. This test isolates the splice pack SP306 serial data circuits.
23. This test isolates the rest of the splice pack SP205 serial data circuits.
27. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
28. The communication malfunction may have prevented diagnosis of the customer complaint.