DTC P0622 Diesel

Circuit Description

The engine control module (ECM)/powertrain control module (PCM) uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator. The generator field duty cycle signal circuit connects to the high side of the field winding in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field winding ON and OFF. The ECM/PCM uses the PWM signal input to determine the generator load on the engine. This allows the ECM/PCM to adjust the idle speed to compensate for high electrical loads.

The ECM/PCM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the ECM/PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5 percent and 100 percent. The ECM/PCM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the ECM/PCM detects an out of range PWM signal, DTC P0622 will set. 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 P0622 Generator F-Terminal Circuit

Conditions for Running the DTC

Key ON Test

Run Test

Conditions for Setting the DTC

Action Taken When the DTC Sets

Conditions for Clearing the DTC

Diagnostic Aids

On vehicles equipped with a sense circuit connected to the voltage regulator. This circuit must have voltage for the charging system to operate properly. This circuit is used as a reference to control system voltage. All circuits must be tested at the generator before replacing any components. refer to system schematic to confirm if the vehicle being serviced uses the sense circuit as part of the charging system.

Step	Action	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	Go to Diagnostic System Check - Vehicle
2	If DTC  P0621 is also set diagnose that DTC first, refer to Diagnostic Aids. Install a scan tool. Start the engine. With a scan tool, monitor the DTC information for DTC P0622. Does the scan tool indicate that DTC P0622 has passed?	Go to Testing for Intermittent Conditions and Poor Connections	Go to Step 3
3	Test the F-terminal signal circuit for a short to voltage, short to ground or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition?	Go to Step 6	Go to Step 4
4	Inspect for poor connections at the harness connector of generator. Refer to Connector Repairs . Did you find and correct the condition?	Go to Step 6	Go to Step 5
5	Replace the Generator. Refer to Generator Replacement . Did you compete the replacement?	Go to Step 6	--
6	Review and record the scan tool Fail Records data. Clear any DTCs. Operate the vehicle within the Fail Records conditions as noted. Using a scan tool, monitor the Specific DTC info for this DTC. Does the scan tool indicate that this DTC failed this ignition?	Go to Step 2	System OK

DTC P0622 Gas

Diagnostic Instructions

DTC Descriptor

DTC P0622: Generator F-Terminal Circuit

Circuit/System Description

The engine control module (ECM)/powertrain control module (PCM) uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator. The generator field duty cycle signal circuit connects to high side of the field windings in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field windings ON and OFF. The ECM/PCM uses the PWM signal input to determine the generator load on the engine. This allows the ECM/PCM to adjust the idle speed to compensate for high electrical loads. The ECM/PCM monitors the status of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the ECM/PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5-95 percent.

Conditions for Running the DTC

Conditions for Setting the DTC

The ECM/PCM detects an out of range PWM signal during the KEY ON test the ECM/PCM detects, a PWM signal greater than 65 percent for at least 5 seconds or during the RUN test a PWM signal less than 5 percent for at least 15 seconds.

Action Taken When the DTC Sets

Conditions for Clearing the DTC

Diagnostic Aids

On vehicles equipped with a sense circuit connected to the voltage regulator. This circuit must have voltage for the charging system to operate properly. This circuit is used as a reference to control system voltage. All circuits must be tested at the generator before replacing any components. refer to system schematic to confirm if the vehicle being serviced uses the sense circuit as part of the charging system.

Reference Information

Schematic Reference

Starting and Charging Schematics

Connector End View Reference

Engine Electrical Connector End Views

Description and Operation

Charging System Description and Operation

Electrical Information Reference

Scan Tool Reference

Circuit/System Verification

With the scan tool installed, ignition ON and the engine running, observe the GEN-F Terminal Signal parameter in the ECM/PCM data list. The GEN-F Terminal Signal parameter should read between 5-95 percent.

Circuit/System Testing

1. If DTC  P0621 is also set diagnose that DTC first, refer to Diagnostic Aids.
2. Ignition OFF, disconnect the generator harness connector.
3. The ignition ON, engine OFF, connect a test lamp to battery positive voltage and repeatedly probe the generator field duty cycle circuit, harness side while monitoring the GEN-F Terminal Signal Parameter in the data list. It should change from less than 5 percent to above 95  percent.

⇒	If the GEN-F Terminal Signal parameter was not affected by the test lamp, test the GEN-F Terminal Signal circuit for a short to ground, a high resistance, an open circuit. If the circuit tests normal replace the ECM/PCM.

4. If the circuit test normal during the Ignition ON/Run tests, and the ECM/PCM parameter changed from less than 5 percent to above 95  percent replace the generator.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.