Circuit Description
The powertrain control module (PCM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the PCM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. When the PCM turns ON the high side driver, the voltage regulator turns ON the field circuit. When the PCM turns OFF the high side driver, the voltage regulator turns OFF the field circuit.
The PCM monitors the state of the generator turn on signal circuit. The PCM 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 PCM should detect a high generator turn on signal circuit. The PCM performs key ON and RUN tests to determine the status of the generator turn on signal circuit. During the key ON test, if the PCM detects a high generator turn on signal circuit voltage, DTC P0621 will set. DTC P0621 will also set if, during the RUN test, the PCM detects a low generator turn on signal circuit. When the DTC sets, the PCM will send a class 2 serial data message to the instrument panel cluster (IPC) to illuminate the charge indicator or display a warning message if equipped.
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 PCM detects a high signal voltage on the generator turn on signal circuit for at least 5 seconds. |
| • | During the RUN test, the PCM detects a low signal voltage on the generator turn on signal circuit for at least 15 seconds. |
Action Taken When the DTC Sets
| • | The PCM will not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM 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 | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Engine Electrical 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 that the voltage is above the specified value? | 13 V | Go to Step 4 | Go to Step 5 |
4 |
Is the voltage less than the specified value? | 5 V | Go to Step 7 | Go to Step 6 |
5 | Test the battery positive voltage circuit of the generator 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 Step 7 |
6 | Test the generator turn on signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 |
7 | Inspect for poor connections at 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 powertrain control module (PCM). Refer to Connector Repairs. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
9 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls 2.2L or Powertrain Control Module Replacement in Engine Controls 4.3L. Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Does the scan tool indicate that DTC P0621 failed this ignition? | -- | Go to Step 3 | System OK |
