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 an ignition 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 instrument panel cluster (IPC) and driver information center (DIC) to illuminate the charge indicator or display a charging message.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0625 Generator F-Terminal Circuit Low Voltage
Conditions for Running the DTC
| • | No crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set. |
| • | The engine speed is less than 3,000 RPM. |
| • | The engine runs continuously. |
| • | Turn the ignition ON. |
| • | DTC P0625 runs continuously once the above condition is met for more than 40 seconds. |
Conditions for Setting the DTC
The ECM detects a PWM signal less than 5 percent for a accumulated 50 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 Failure 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: Engine Controls Schematics Connector End View Reference: Engine Control Module 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 parameter is within the specified range? | 5-100% | Go to Testing for Intermittent Conditions and Poor Connections | 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 . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 6 |
5 | Test the battery positive voltage cable for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7 |
6 | Test the GEN L-Terminal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 |
7 | Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs . 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 . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
9 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Is the action complete? | -- | Go to Step 10 | - |
10 |
Does the scan tool indicate that DTC P0625 failed? | -- | Go to Step 2 | System OK |
