Diagnostic Instructions
Diagnostic System Check - Vehicle
DTC Descriptor
DTC P0622: Generator F-Terminal Circuit
Circuit/System Description
The engine control module (ECM)/powertrain control module (PCM) uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator. The generator field duty cycle signal circuit connects to high side of the field windings in
the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field windings ON and OFF. The ECM/PCM uses the PWM signal input to determine the generator load on the engine. This allows the ECM/PCM to adjust the idle speed
to compensate for high electrical loads. The ECM/PCM monitors the status of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the ECM/PCM should detect a duty cycle near 0 percent. However, when
the engine is running, the duty cycle should be between 5-95 percent.
Conditions for Running the DTC
| • | The vehicle speed is above 8 km/h (5 mph). |
| • | The system voltage is between 9.5-18 volts. |
Conditions for Setting the DTC
The ECM/PCM detects an out of range PWM signal during the KEY ON test the ECM/PCM detects, a PWM signal greater than 65 percent for at least 5 seconds or during the RUN test a PWM signal less than 5 percent 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 ECM/PCM will command the message OFF after one trip in which the diagnostic test has been run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
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
Description and Operation
Charging System Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
With the scan tool installed, ignition ON and the engine running, observe the GEN-F Terminal Signal parameter in the ECM/PCM data list. The GEN-F Terminal Signal parameter should read between 5-95 percent.
Circuit/System Testing
- If DTC P0621 is also set diagnose that DTC first, refer to Diagnostic Aids.
- Ignition OFF, test for B+ between the generator B+ output terminal (stud) to ground.
| ⇒ | If less than the specified range, test the B+ circuit for a short to ground, an open or a high resistance. |
- Ignition OFF, disconnect the generator harness connector.
- The ignition ON, engine OFF, connect a test lamp to battery positive voltage and repeatedly probe the generator field duty cycle circuit, harness side while monitoring the GEN-F Terminal Signal Parameter in the data list. It should change from less
than 5 percent to above 95 percent.
| ⇒ | If the GEN-F Terminal Signal parameter was not affected by the test lamp, test the GEN-F Terminal Signal circuit for a short to ground, a high resistance, an open circuit. If the circuit tests normal replace the ECM/PCM. |
- If the circuit test normal during the Ignition ON/Run tests, and the ECM/PCM parameter changed from less than 5 percent to above 95 percent replace the generator.
Repair Instructions
