Circuit 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 the high side of the field winding in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field winding 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 state 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 percent and 100 percent. The ECM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the ECM detects an out of range PWM signal, DTC P0622 will set. When the DTC sets, the ECM will send a class 2 serial data message to the instrument panel cluster (IPC) to illuminate the charge indicator.
Conditions for Running the DTC
Key ON Test
| • | No generator, CKP sensors, or CMP sensor DTCs are set. |
| • | The key is in the RUN position. |
| • | The engine is not running. |
Run Test
| • | No generator, CKP sensors, or CMP sensor DTCs are set. |
| • | The engine is less than 3,000 RPM. |
Conditions for Setting the DTC
| • | During the ignition ON test, the ECM detects a PWM signal is between 10-40 percent for more than 6 seconds. |
| • | During the RUN test, the ECM detects a PWM signal less then 5 percent for more than 6 seconds. |
Action Taken When the DTC Sets
| • | The ECM will store the conditions present when the DTC set as Fail Records data only. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
Conditions for Clearing the DTC
| • | The Conditions for Setting the DTC are no longer present. |
| • | A history DTC will clear after 40 malfunction free ignition cycles. |
| • | The ECM receives the clear code command from the scan tool. |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Engine Electrical Connector End Views | |||
1 | Did you perform the Engine Electrical Diagnostic System Check? | Go to Step 2 | |
2 |
Does the scan tool indicate that DTC P0622 has passed? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
3 | Test the generator turn on signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 6 | Go to Step 4 |
4 | Inspect for poor connections at the harness connector of the ECM. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 6 | Go to Step 5 |
5 | Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data in Engine Controls-7.8L. Did you compete the replacement? | Go to Step 6 | -- |
6 |
Does the scan tool indicate that this DTC failed this ignition? | Go to Step 2 | System OK |
