Circuit Description
The engine control module (ECM) uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator and fault indication. 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 engine is running, the ECM should detect a duty cycle that varies up to 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, a DTC will set. When the DTC sets, the ECM will send a class 2 serial data message to the IPC and DIC to illuminate the charge indicator or display a charging message.
Conditions for Running the DTC
| • | No generator, CKP sensors, or CMP sensor DTCs are set. |
| • | The engine is less than 3000 RPM. |
| • | The generator has not been commanded OFF by the ECM or scan tool. |
Conditions for Setting the DTC
The ECM detects a PWM signal less than 5 percent for at least 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. |
| • | The ECM will send a class 2 serial data message to the IPC and DIC to illuminate the charge indicator or display a charging message. |
Conditions for Clearing the MIL/DTC
| • | The conditions for setting DTC P0625 are not present. |
| • | 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 in Engine Controls-4.6L (LH2) | ||||
1 | Did you perform the Vehicle Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic Starting Point - Computer/Integrating Systems in Computer/Integrating Systems |
2 |
Does the scan tool indicate that the GEN - F Terminal parameter is within the specified range? | 5-100% | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
3 |
Is the GEN - F Terminal Signal parameter affected? | -- | Go to Step 5 | Go to Step 4 |
4 | Test the generator field duty cycle signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 |
5 | Test the battery positive voltage cable for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7 |
6 | Test the GEN L-Terminal circuit cable for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | |
7 | Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Charging System Test |
8 | 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 10 | Go to Step 9 |
9 |
Important: The replacement ECM must be programmed. Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls-4.6L (LH2). Is the action complete? | -- | Go to Step 10 | -- |
10 |
Does the scan tool indicate that DTC P0625 failed? | -- | Go to Step 2 | System OK |
