Circuit Description
The ECM uses the charge indicator control 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 charge indicator control circuit. The ECM should detect a low generator turn on signal circuit voltage when the key is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect a high charge indicator control circuit. The ECM performs key ON and RUN tests to determine the status of the charge indicator control circuit. During the key ON test, if the ECM detects a high generator turn on signal circuit voltage, DTC P0621 will set. DTC P0621 will also set if, during the RUN test, the ECM detects a low generator turn on signal circuit. When the DTC sets, the ECM will turn on the charge indicator in the IPC.
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The engine speed is more than 1000 RPM. |
Conditions for Setting the DTC
| • | The ECM detects the GEN L-Terminal active with the ignition ON. |
| • | The ECM detects the GEN L-Terminal inactive with the engine operating. |
| • | The above conditions are present for 6 seconds. |
Action Taken When the DTC Sets
| • | The ECM will record the operating conditions presents when the DTC set as Failure Records data only. |
| • | The instrument panel cluster (IPC) displays a message. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
Conditions for Clearing the DTC
| • | The Conditions for Setting the DTC are no longer present. |
| • | A history DTC will clear after 40 malfunction free ignition cycles. |
| • | The Engine Control Module (ECM) receives the clear code command from the scan tool. |
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Engine Electrical Connector End Views | ||||
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? | -- | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
3 |
Is voltage at or above specified valve? | 3.0 V | Go to Step 5 | Go to Step 4 |
4 | Test the charge indicator control circuit for a short or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 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 in Wiring Systems. 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 Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7 |
7 |
Important: The replacement ECM must be programmed. Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 6.6L Is action complete? | -- | Go to Step 8 | -- |
8 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
