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 ignition is in the ON position, with the engine OFF, the ECM should detect a duty cycle that is 0 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.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0626 GEN F-Terminal Circuit High Voltage
Conditions for Running the DTC
| • | No crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set. |
| • | The engine is not running. |
| • | The ignition is in the ON position. |
| • | DTC P0626 runs continuously once the above condition is met for more than 15 seconds. |
Conditions for Setting the DTC
The ECM detects a PWM signal is greater than 65 percent for an accumulated of 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 instrument panel cluster (IPC) and driver information center (DIC) to illuminate the charge indicator or display a charging message. |
Conditions for Clearing the MIL/DTC
| • | The conditions for setting DTC P0626 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? | 0-5% | 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 battery voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 6 |
5 | 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 8 | Go to Charging System Test |
6 | 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 8 | Go to Step 7 |
7 | Replace the ECM. Refer to Control Module References . Is the action complete? | -- | Go to Step 8 | -- |
8 |
Does the scan tool indicate that DTC P0626 failed? | -- | Go to Step 2 | System OK |
