Diagnostic Instructions
DTC Descriptor
DTC P0621: Generator L-Terminal Circuit
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
Generator Turn ON Signal
| P0621
| P0621
| P0621
| P0621
|
Circuit/System Description
The engine control module (ECM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field
circuit ON and OFF. The ECM monitors the state of the generator turn on signal circuit. The ECM should detect low voltage on generator turn on signal circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine
running, the ECM should detect high voltage on the generator turn on signal circuit. The ECM performs Ignition ON and RUN tests to determine the status of the generator turn on signal circuit.
Conditions for Running the DTC
Ignition ON Test
| • | No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set. |
| • | The ignition is in RUN position. |
| • | The engine is not running. |
Run Test
| • | No generator, CKP sensors, CMP sensor DTCs are set. |
Conditions for Setting the DTC
| • | During the Ignition ON test, the ECM detects high voltage on the generator turn on signal circuit for 5 seconds. |
| • | During the RUN test, the ECM detects low voltage on the generator turn on signal circuit for 15 seconds. |
Action Taken When the DTC Sets
| • | The ECM will command the charge indicator and or warning message to be illuminated on the instrument panel cluster (IPC) and the driver information center (DIC), if equipped. |
| • | The ECM will not illuminate the malfunction indicator lamp (MIL). |
| • | The ECM will store conditions, which were present when the DTC set as Failure Records data only. |
Conditions for Clearing the DTC
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | Using the scan tool Clear DTC Information function can clear the DTC. |
Diagnostic Aids
On vehicles equipped with a sense circuit connected to the voltage regulator.This circuit must have voltage for the charging system to operate properly.This circuit is used as a reference to control system voltage. All circuits must be tested at the generator
before replacing any components. refer to system schematic to confirm if the vehicle being serviced uses the sense circuit as part of the charging system.
Reference Information
Schematic Reference
Starting and Charging Schematics
Connector End View Reference
Engine Electrical Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the generator.
- Ignition OFF, test for B+ between the generator sense circuit terminal D and ground.
| ⇒ | If less than the specified range, test the generator sense circuit for a short to ground, an open/high resistance. |
- Ignition ON, test for less than 1 volt between the generator turn on signal terminal B and ground.
| ⇒ | If greater than the specified range, test the generator turn on signal circuit for a short to voltage. If the circuit tests normal, replace the ECM. |
- Engine running, test for greater than 3.5 volts between the generator turn on signal and ground.
| ⇒ | If less than the specified range, test the generator turn on signal circuit for a short to ground, an open/high resistance. If the circuit tests normal, replace the ECM. |
- If the circuit test normal, replace the generator.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
