U0120-LOST COMMUNICATION WITH STARTER/GENERATOR CONTROL MODULE

For a complete wiring diagram, refer to the Wiring Information.

When Monitored:
Continuously with the ignition on.
Set Condition:
The Powertrain Control Module (PCM) doesn't receive a Bus Message from the Generator.

Possible Causes
(D509) LIN BUS CIRCUIT SHORTED TO VOLTAGE
(D509) LIN BUS CIRCUIT SHORTED TO GROUND
(D509) LIN BUS CIRCUIT OPEN/HIGH RESISTANCE
GENERATOR
POWERTRAIN CONTROL MODULE (PCM)

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

1. DTC IS ACTIVE

1.	Ignition on, engine not running.

2.	With the scan tool, clear DTCs in the PCM.

3.	Start the engine.

4.	Allow the engine to reach normal operating temperature.

5.	With the scan tool, select View DTCs.

Is the status Active for this DTC?

Yes

Go To 2

(Refer to 29 - Non-DTC Diagnostics/Communication - Diagnosis and Testing) and perform the Stored Lost Communication DTCs diagnostic procedure.

2. CHECK THE (D509) LIN BUS CIRCUIT FOR A SHORT TO VOLTAGE

1.	Turn the ignition off.

2.	Disconnect the Generator C2 harness connector.

3.	Disconnect the PCM C1 harness connector.

4.	Remove the ASD Relay.

5.	Connect a jumper between terminal 30 and terminal 87.

6.	Turn the ignition on.

7.	Measure the voltage of the (D509) LIN BUS circuit at the Generator C2 harness connector.

Is there any voltage present?

Yes

Go To 3

Repair the (D509) LIN BUS circuit for a short to voltage.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

3. CHECK THE (D509) LIN BUS CIRCUIT FOR A SHORT TO GROUND

1.	Turn the ignition off.

2.	Remove the jumper.

3.	Reinstall the ASD Relay.

4.	Measure the resistance between ground and the (D509) LIN BUS circuit at the Generator C2 harness connector.

Is the resistance above 10k Ohms?

Yes

Go To 4

Repair the (D509) LIN BUS circuit for a short to ground.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

4. CHECK THE (D509) LIN BUS CIRCUIT FOR AN OPEN/HIGH RESISTANCE

1.	Measure the resistance of the (D509) LIN BUS circuit between the Generator C2 harness connector and the PCM C1 harness connector.

Is the resistance below 5.0 Ohms?

Yes

Go To 5

Repair the (D509) LIN BUS circuit for an open or high resistance.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

5. GENERATOR

1.	Replace the Generator in accordance with the service information.

2.	Reconnect the PCM C1 harness connector.

3.	Reconnect the Generator C2 harness connector.

4.	Start the engine.

5.	Allow the engine to reach normal operating temperature.

6.	With the scan tool, select View DTCs.

Did the DTC return?

Yes

Go To 6

Test complete
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

6. POWERTRAIN CONTROL MODULE

1.	Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Oxygen Sensor and the Powertrain Control Module.

2.	Look for any chafed, pierced, pinched, or partially broken wires.

3.	Look for broken, bent, pushed out or corroded terminals.

4.	Perform any Technical Service Bulletins that may apply.

Were any problems found?

Yes

Repair as necessary.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

Replace the Powertrain Control Module in accordance with the service information.
Perform the PCM VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

U0120-LOST COMMUNICATION WITH STARTER/GENERATOR CONTROL MODULE

U0120-LOST COMMUNICATION WITH STARTER/GENERATOR CONTROL MODULE

Possible Causes