P0621

DTC P0621

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 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.

Test

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