Diagnostic Instructions
DTC Descriptor
DTC P0622: Generator F-Terminal Circuit
Circuit/System Description
The engine control module (ECM) 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 uses the PWM signal input to determine the generator load on the engine. This allows the ECM to adjust the idle speed to compensate for high electrical loads. The ECM
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 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 detects an out of range PWM signal during the KEY ON test. |
| • | The ECM detects a PWM signal greater than 65 percent for at least 5 seconds |
| • | The ECM detects a PWM signal less than 5 percent for at least 15 seconds during the RUN test. |
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 ECM 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. |
| • | Using the scan tool Clear DTC Information function can clear the DTC. |
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 Verification
With the scan tool installed, ignition ON and the engine running, observe the GEN-F Terminal Signal parameter in the ECM data list. The GEN-F Terminal Signal parameter should read between 5-95 percent.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the generator.
- Ignition ON, and the 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 ECM data list. It should change
from 0 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 voltage, short to ground, a high resistance, or an open circuit. If the circuit tests normal, replace the ECM. |
- If the circuit tests normal during the Ignition ON / RUN tests, and the ECM parameter changed from 0 percent to above 95 percent, replace the generator.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
