Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC P0621: Generator L-Terminal CircuitDiagnostic 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. |
| • | The engine is running. |
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
DTC P0621 is a C Type DTC.
Conditions for Clearing the DTC
DTC P0621 is a C Type 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
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
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.
- Ignition ON, test for less than 1 volt between the generator turn on signal terminal B and ground.
- Engine running, test for greater than 3.5 V between the generator turn on signal and ground.
- If the circuit tests normal, replace the generator.
| ⇒ | If less than the specified range, test the generator sense circuit for a short to ground, an open/high resistance. |
| ⇒ | 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. |
| ⇒ | 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
