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 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
| • | The ignition is ON. |
| • | The engine speed is more than 1,000 RPM. |
Conditions for Setting the DTC
| • | The ECM detects the GEN L-Terminal active with the ignition ON. |
| • | The ECM detects the GEN L-Terminal inactive with the engine operating. |
| • | The above conditions are present for 6 seconds. |
Action Taken When the DTC Sets
| • | The ECM will record the operating conditions presents when the DTC set as Failure Records data only. |
| • | The IPC displays a message. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
Conditions for Clearing the DTC
| • | The Conditions for Setting the DTC are no longer present. |
| • | A history DTC will clear after 40 malfunction free ignition cycles. |
| • | The ECM receives the clear code command from the scan tool. |
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 |
Does the voltage read the indicated values? | Engine Off = 0 - 0.5 V Engine On = 4.5 - 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 ECM. Refer to Connector Repairs. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
9 | Replace the ECM. 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 |
