Circuit Description
The engine control module (ECM) uses the generator turn ON signal circuit to control the load of the generator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. When the ECM turns ON the high side driver, the voltage regulator turns ON the field circuit. When the ECM turns OFF the high side driver, the voltage regulator turns OFF the field circuit.
The ECM monitors the state of the generator turn ON signal circuit. With the engine running, the ECM should detect a high generator turn ON signal circuit, or when the charging system malfunctions. If the ECM detects a low generator turn ON signal circuit, DTC P0621 will set. When the DTC sets, the ECM will send a serial data message to the instrument panel cluster (IPC) to illuminate the charge indicator.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0621 Generator L-Teminal Circuit
Conditions for Running the DTC
| • | No generator, crankshaft position (CKP) sensor, or camshaft position (CMP) sensor DTCs are set. |
| • | The engine is running. |
Conditions for Setting the DTC
The ECM detects a low signal voltage on the generator turn on signal circuit for at least 5 seconds.
Action Taken When the DTC Sets
| • | The ECM sends a serial data message to the IPC to illuminate the charge indicator. |
| • | 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. |
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: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that DTC P0621 has passed this ignition cycle? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 |
3 |
Does the scan tool indicate a change in voltage each time the generator L-terminal is commanded ON and OFF? | -- | Go to Step 6 | Go to Step 4 |
4 |
Is the voltage within the specified range? | 4.5-5.5 V | Go to Step 7 | Go to Step 5 |
5 | Test the generator turn ON signal circuit for a short to ground or open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 |
6 | Test the generator battery voltage output circuit for a high resistance or open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Charging System Test |
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. Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Does the scan tool indicate that DTC P0621 failed? | -- | Go to Step 3 | System OK |
