Diagnostic Instructions
DTC Descriptor
DTC P0621 : Generator L-Terminal Circuit
Circuit/System Description
The engine control module (ECM)/powertrain control module (PCM) uses the generator turn ON signal circuit to control the load of the generator on the engine. A high side driver in the ECM/PCM applies a voltage to the voltage regulator. This signals the
voltage regulator to turn the field circuit ON and OFF. The ECM/PCM monitors the state of the circuit. The ECM/PCM should detect low voltage on circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running,
the ECM/PCM should detect high voltage on the circuit. The ECM/PCM performs key a ON and RUN test to determine the status of the circuit.
Conditions for Running the DTC
Key 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 key ON test, the ECM/PCM detects high voltage on the generator turn ON signal circuit for at least 5 seconds. |
| • | During the RUN test the ECM/PCM detects low voltage on the generator turn ON signal circuit for at least 15 seconds. |
Action Taken When the DTC Sets
| • | The ECM/PCM 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/PCM will not illuminate the malfunction indicator lamp (MIL). |
| • | The ECM/PCM will store conditions, which were present when the DTC set as Fail Records data only. |
Conditions for Clearing the DTC
The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
Reference Information
Schematic Reference
Starting and Charging Schematics
Connector End View Reference
Engine Electrical Connector End Views
Description and Operation
Charging System Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the generator.
- Ignition ON, test for less than 1 volt between the generator turn ON signal circuit terminal B and ground.
| ⇒ | If greater than the specified range, test the circuit for a short to voltage. If the circuit tests normal, replace the ECM/PCM. |
- Engine running, test for greater than 3.5 volts between the generator turn ON signal circuit terminal B and ground.
| ⇒ | If less than the specified range, test the circuit for a short to ground, an open or a high resistance. If the circuit tests normal, replace the ECM/PCM. |
- If the circuit test normal, replace the generator.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
