Circuit Description
The PCM uses the F-terminal circuit to monitor the duty cycle of the field circuit. The F-terminal 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 PCM uses the PWM signal input to determine the generator load on the engine. This allows the PCM to adjust the idle speed to compensate for high electrical loads.
The PCM monitors the state of the F-terminal circuit. When the key is in the RUN position and the engine is OFF, the PCM 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 PCM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the PCM detects an out of range PWM signal, DTC P0622 will set. When the DTC sets, the PCM will send a class 2 serial data message to illuminate the appropriate telltales.
Conditions for Running the DTC
Key ON Test
| • | Generator, CKP sensors, or CMP sensor DTCs are not set. |
| • | The key is in the RUN position. |
| • | The engine is not running. |
Run Test
| • | Generator, CKP sensors, or CMP sensor DTCs are not set. |
| • | The engine is less than 3000 RPM. |
Conditions for Setting the DTC
| • | During the key ON test, the PCM detects a PWM signal more than 65 percent for at least 5 seconds. |
| OR |
| • | During the RUN test, the PCM detects a PWM signal less than 5 percent for at least 15 seconds. |
Action Taken When the DTC Sets
| • | The PCM will not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM will store the conditions present when the DTC set as Failure Records data only. |
Conditions for Clearing the MIL/DTC
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
The PCM uses the L-terminal circuit to apply a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. Therefore, if an L-terminal circuit conditions exists that causes the voltage regulator to improperly control the generator field, DTC P0622 will set. DTC P0621 may also set.
If the condition is intermittent, refer to Intermittent Conditions .
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||
2 | Is DTC P0621 also set? | -- | ||||||||
3 | Observe the L-Terminal display on the scan tool. Does the L-Terminal display indicate OK? | -- | Go to Diagnostic Aids | |||||||
4 |
Is the test lamp ON? | -- | ||||||||
5 |
Did you find and correct the condition? | -- | Go to Generator Replacement in Engine Electrical | |||||||
6 |
Does the Generator PWM indicate a PWM near the specified value? | 100% | ||||||||
7 |
Did you find and correct the condition? | -- | ||||||||
8 |
Does the DMM indicate a voltage near the specified value? | 5V | ||||||||
9 |
Did you find and correct the condition? | -- | ||||||||
10 |
Did you find and correct the condition? | -- | Go to Generator Replacement in Engine Electrical | |||||||
11 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |||||||
12 |
Does the scan tool indicate that DTC P0622 passed? | -- | System OK |
