DTC P0621
Diagnostic Instructions
DTC Descriptor
DTC P0621: Alternator L- Terminal Circuit
Circuit/System Description
The powertrain control module (PCM) uses the alternator turn on signal circuit to control the load of the alternator on the engine. A high side driver in the PCM applies a voltage to the voltage regulator. 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 alternator turn on signal circuit. With the engine running, the PCM should detect a high alternator turn on signal circuit, or when the charging system malfunctions. If the PCM detects a low alternator turn on signal circuit, DTC P0621 will set.
Conditions for Running the DTC
Key ON Test
| • | The ignition is in RUN position. |
| • | The engine is not running. |
RUN Test
| • | The engine speed is less than 3,000 RPM. |
Conditions for Setting the DTC
| • | During the key ON test, the PCM detects high voltage on the alternator turn on signal circuit for at least 5 seconds. |
| • | During the RUN test the PCM detects low voltage on the alternator turn on signal circuit for at least 15 seconds. |
Action Taken When the DTC Sets
| • | The PCM will command the charge indicator and or warning message to be illuminated on the instrument panel cluster (IPC) and the driver information centre (DIC), if equipped. |
| • | The PCM will not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM will store conditions, which were present when the DTC set as Fail Records data only. |
Conditions for Clearing the DTC
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | Using the scan tool Clear DTC Information function can clear the DTC. |
Circuit/System Testing
- Verify that a test lamp illuminates between the G13 alternator B+ terminal 1 X2 and ground.
| ⇒ | If the test lamp does not illuminate and the circuit fuse is good
|
| 1.2. | Test for less than 2 Ω in the B+ circuit end to end. |
| ⇒ | If 2 Ω or greater, repair the open/high resistance in the circuit. |
| ⇒ | If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse. |
| ⇒ | If the test lamp does not illuminate and the circuit fuse is open
|
| 1.2. | Test for greater than 100 Ω between the B+ circuit and ground. |
| ⇒ | If 100 Ω or less, repair the short to ground on the circuit. |
| ⇒ | If greater than 100 Ω, replace the alternator. |
| ⇓ | If the test lamp illuminates
|
- Ignition OFF, disconnect the X1 harness connector at the alternator, ignition ON.
- Test for 3.5V or greater between the control circuit terminal B X1 and ground.
| 3.1. | Ignition OFF, disconnect the harness connectors at the ECM. |
| 3.2. | Test for infinite resistance between the control circuit and ground. |
| ⇒ | If less than infinite resistance, repair the short to ground on the circuit. |
| 3.3. | Test for less than 2 Ω in the control circuit end to end. |
| ⇒ | If greater the 2 Ω, repair the open/high resistance in the circuit. |
| ⇒ | If less than 2 Ω, replace the ECM. |
| 3.1. | Ignition OFF, disconnect the harness connectors at the ECM. |
| 3.2. | Test for less than 1 V between the control circuit and ground. |
| ⇒ | If less than 1 V, replace the G13 Alternator. |
| ⇒ | If 1 V or greater, repair the short to voltage on the circuit. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for PCM replacement, setup, and programming
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