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 Ignition 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 serial data message to the drivers information center (DIC) to display a warning message.
DTC Descriptor
This diagnostic procedure supports the following DTC: DTC P0622 Generator F-Terminal Circuit
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Generator Field Duty Cycle Signal | P0622 | P0622 | P0622 | P0622 |
Conditions for Running the DTC
Ignition ON Test
| • | No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set. |
| • | The Ignition 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 greater than 65 percent for 5 seconds. |
| • | During the RUN test, the ECM detects a PWM signal less than 5 percent for 15 seconds. |
Action Taken When the DTC Sets
| • | The ECM will not illuminate the malfunction indicator lamp (MIL). |
| • | The ECM will store the conditions present when the DTC set as Fail 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. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Engine Control Module Connector End Views for the 6.0L (LS2) engine, or Engine Control Module Connector End Views for the 7.0L (LS7) engine, or Engine Electrical Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the GEN-F Terminal Signal parameter is within the specified range? | 5-95% | Go to Step 3 | Go to Step 4 |
3 | With the scan tool, command the generator OFF. Does the GEN-F Terminal Signal equal the specified value? | 0% | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 4 |
4 |
Is the GEN-F Terminal Signal parameter near the specified value? | 100% | Go to Charging System Test | Go to Step 5 |
5 | Test the generator field duty cycle signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 6 |
6 | Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Connector Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7 |
7 |
Important: The replacement ECM must be programmed. Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 8 | -- |
8 |
Does the scan tool indicate that DTC P0622 failed this ignition? | -- | Go to Step 2 | System OK |
