DTC P0621 Generator L-Terminal Circuit. Cadillac Seville 2000

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2000 🢒 Seville 🢒 DTC 🢒 DTC P0621 Generator L-Terminal Circuit

Engine Electrical Component Views
Generator, PCM, Steering Pressure Switch and Oil Level Switch
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The PCM uses the L-terminal 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 L-terminal circuit. The PCM should detect a low L-terminal 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 L-terminal voltage. The PCM performs key ON and RUN tests to determine the status of the L-terminal circuit. During the key ON test, if the PCM detects a high L-terminal voltage, DTC P0621 will set. DTC P0621 will also set if, during the RUN test, the PCM detects a low L-terminal voltage. When the DTC sets, the PCM will send a class 2 serial data message to illuminate the charging telltale.

Conditions for Running the DTC

Key ON Test

•	No generator, CKP sensors, or 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 L-terminal circuit for at least 5 seconds.

•	During the RUN test, the PCM detects a low signal voltage on the L-terminal 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	Values	Yes	No
1	Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Is DTC P0622 also set?	--	Go to DTC P0622 Generator F-Terminal Circuit	Go to Step 3
3	Observe the L-Terminal display on the scan tool. Does the L-Terminal display NO OUTPUT?	--	Go to Diagnostic Aids	Go to Step 4
4	Turn OFF the ignition. Disconnect the generator connector. Turn ON the ignition, with the engine OFF. Observe the L-Terminal display on the scan tool. Does the L-Terminal display NO OUTPUT	--	Go to Generator Replacement in Engine Electrical	Go to Step 5
5	Test the L-Terminal circuit for a short to voltage. If the condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to Step 7	Go to Step 6
6	Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete?	--	Go to Step 7	--
7	Review and record the scan tool Fail Records data. Clear the DTCs. Operate the vehicle with the parameters listed in the Conditions for Running the DTC. Monitor the scan tool Specific DTC Information for DTC P0621 until the test runs. Does the scan tool indicate that DTC P0621 passed?	--	System OK	Go to Step 2