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. 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 class 2 serial data message to the instrument panel cluster (IPC) to illuminate the charge indicator.
Conditions for Running the DTC
Key ON Test
| • | The key is in the ON position for 5 seconds. |
| • | The engine is OFF. |
Engine Run Test
| • | The engine is running. |
| • | The engine speed is less than 3,000 RPM. |
Conditions for Setting the DTC
During key ON test, the ECM detects a high signal voltage on the generator turn on signal circuit for at least 5 seconds.
During the RUN test, the ECM detects a low signal voltage on the generator turn on signal circuit for at least 10 seconds.
Action Taken When the DTC Sets
| • | The ECM sends a class 2 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 Fail Records data only. |
| • | The Service Vehicle Soon (SVS) light may be illuminated. |
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 |
|---|---|---|---|---|
Connector End View Reference: Engine Electrical Connector End Views , Engine Control Module Connector End Views in Engine Controls - 2.2L (L61), or Powertrain Control Module Connector End Views in Engine Controls - 3.5L (L66) | ||||
1 | Did you perform the Engine Electrical Diagnostic System Check? | -- | 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 in Wiring Systems | Go to Step 3 |
3 |
Does the scan tool indicate a change in voltage each time the Generator L - Terminal is commanded Off and On? | -- | 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, high resistance or open. 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 |
6 | Test the generator battery voltage output circuit for a high resistance or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 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 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 engine control module (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 - 2.2L (L61) or Powertrain Control Module Replacement in Engine Controls - 3.5L (L66). 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 |
