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. 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 generator turn on signal circuit. The ECM performs key ON and RUN tests to determine the status of the generator turn on signal 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 send a serial data message to the drivers information center (DIC) to display a warning message.
DTC Descriptor
This diagnostic procedure supports the following DTC: DTC P0621 Generator L-Terminal Circuit
Conditions for Running the DTC
Key ON Test
| • | No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set. |
| • | The key is in the RUN position. |
| • | The engine is not running. |
Run Test
| • | No generator, CKP sensors, or CMP sensor DTCs are set. |
| • | The engine is running. |
Conditions for Setting the DTC
| • | During the 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 15 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 Fail 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. |
Diagnostic Aids
Vehicles equipped with a sense circuit to the voltage regulator, this circuit is used as a reference to control system voltage. The sense circuit must be operating correctly for the charging system to operate properly. All circuits at the generator should be tested for proper operation before replacing components. Refer the schematic to comfirm if the vehicle being serviced uses the sense circuit as part of charging system.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Engine Control Module Connector End Views in Engine Controls - 6.0L (LS2) or Engine Electrical Connector End Views | |||
1 | Did you perform the Diagnostic System Check-Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
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 | With a scan tool, monitor the DTC information for DTC P0621 and DTC P0622 in Engine Controls. Does the scan tool indicate that DTC P0621 and DTC P0622 have failed? | Go to Step 6 | Go to Step 4 |
4 | Test the generator turn on signal circuit for a short to voltage or an 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 5 |
5 | 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 8 | Go to Step 7 |
6 | Repair the high resistance or open in the battery positive voltage sense circuit of the generator. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 8 | -- |
7 |
Important: The replacement ECM must be programmed. Replace the ECM . Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | Go to Step 8 | -- |
8 |
Does the scan tool indicate that DTC P0621 failed this ignition? | Go to Step 2 | System OK |
