Circuit Description
The engine control module (ECM)/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 ECM/PCM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. When the ECM/PCM turns ON the high side driver, the voltage regulator turns ON the field circuit. When the ECM/PCM turns OFF the high side driver, the voltage regulator turns OFF the field circuit.
The ECM/PCM monitors the state of the generator turn on signal circuit. The ECM/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 ECM/PCM should detect a high generator turn on signal circuit. The ECM/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 ECM/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 ECM/PCM detects a low generator turn on signal circuit. When the DTC sets, the ECM/PCM will send a class 2 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-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/PCM detects a high signal voltage on the generator turn on signal circuit for at least 5 seconds. |
| • | During the RUN test, the ECM/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 ECM/PCM will not illuminate the malfunction indicator lamp (MIL). |
| • | The ECM/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 first value with the generator OFF and greater than the second value with the generator ON? | 0 V 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 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/PCM. Refer to Connector Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
9 |
Important: The replacement ECM/PCM must be programmed. Replace the ECM/PCM. 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 this ignition? | -- | Go to Step 3 | System OK |
