Scan Tool Does Not Communicate with Class 2 Device

SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE

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 15:

Step 16 - Step 20:

The numbers below refer to the step numbers on the diagnostic table.
2. A partial loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication of the class 2 serial data circuit.
4. The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.
- U1300
- U1301
- U1305
6. A State of Health DTC with a history status may be present along with a U1000 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was ON.
10. Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
12. This step uses the loss of communications with a class 2 serial data circuit to locate the probable malfunction.On vehicles equipped with a digital radio receiver (DRR), the DRR must be isolated from the sensing and diagnostic module (SDM) to evaluate the condition of that class 2 serial data circuit branch. The following modules communicate on the class 2 serial data circuit:
- Driver information center (DIC)
- DRR
- Electronic brake control module (EBCM)
- Instrument panel cluster (IPC)
- Head-up display (HUD)
- HVAC
- Powertrain control module (PCM)
- Radio
- Vehicle communication interface module (VCIM)
- SDM
17. If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
18. The communication concern may have prevented diagnosis of the customer complaint.