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 | -- |
Typical Scan Tool Data
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: Engine Running. Parameter Normal Value: OK | |||
Generator Turn On Signal | Fault | Not Run or OK | Not Run or OK |
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: Engine Running. Parameter Normal Value: Not Run or OK | |||
Generator Turn On Signal | Not Run or OK | Not Run or Fault | Not Run or OK |
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: Ignition ON. Parameter Normal Value: OK | |||
Generator Turn On Signal | Not Run or OK | Not Run or OK | Fault |
Circuit/System Description
The engine control module (ECM) uses the generator turn on signal circuit, or L-terminal 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 the 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.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
The ECM detects high or low voltage on the generator turn on signal circuit for 15 seconds.
Action Taken When the DTC Sets
The charge indicator turns ON.
Conditions for Clearing the DTC
| • | The DTC will pass when the conditions for setting the DTC are no longer met for 1 second. |
| • | A 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
Description and Operation
Charging System Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Engine running, observe the following scan tool ECM control circuit status parameters.
| • | GEN L-Terminal Ckt Short Gnd Test Status |
| • | GEN L-Terminal Ckt Open Test Status |
| • | GEN L-Terminal Ckt Short Volts Test Status |
Each parameter should read OK or Not Run.
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 1 and ground.
- Engine running, command the GEN L-Terminal ON with a scan tool. Test for greater than 3.5 volts between the signal circuit terminal 1 and ground.
- If the circuit tests normal, test or replace the generator.
| ⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM. |
| ⇒ | If less than the specified range, test the signal circuit for a short to ground, an open or a 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. |
