Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic approach.

•	Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0622

Generator F-Terminal Circuit

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
B+	P0622	P0621	-	-
Control	P0621	P0621	P0621	-
Signal	P0622	P0622	-	P0622

Circuit/System Description

The engine control module (ECM) uses the generator field duty cycle signal circuit, or F-terminal 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 uses the PWM signal input to determine the generator load on the engine. This allows the ECM to adjust the idle speed to compensate for high electrical loads. The ECM monitors the status of the generator field duty cycle signal circuit. When the ignition is ON and the engine is OFF, the ECM should detect a duty cycle near 0%. When the engine is running, the duty cycle should be between 5-99%.

Conditions for Running the DTC

•	Ignition ON engine OFF, for the Ignition ON test.

•	Engine running, engine speed less than 3 000 RPM for the RUN test.

Conditions for Setting the DTC

•	DTC P0621 is not set.

•	Ignition ON engine OFF, the ECM detects a PWM signal that is greater than 65% for 5 seconds.

•	Engine running, the ECM detects a PWM signal that is less than 5% for 15 seconds.

Action Taken When the DTC Sets

DTC P0622 is a C type DTC.

Conditions for Clearing the DTC

DTC P0622 is a C type DTC.

Reference Information

Schematic Reference

Starting and Charging Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Charging System Description and Operation

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Engine running, observe the scan tool Generator F-Terminal Signal Circuit parameter. The Generator F-Terminal Signal Circuit parameter should display between 5-99%.

Circuit/System Testing

1.	Verify that a test lamp illuminates between the G13 Generator B+ terminal A X1 and ground.

2.	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3.	Ignition OFF, disconnect the X2 harness connector at the G13 Generator.

4.	Ignition ON, verify the scan tool Generator F-Terminal Signal parameter displays less than 5%.

5.	If greater than the specified range, test the signal circuit terminal 2 for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module.

6.	Install a 3 A fused jumper wire between B+ and the signal circuit terminal 2.

7.	Verify the scan tool Generator F-Terminal Signal parameter displays greater than 95%.

8.	If less than the specified range, test the signal circuit terminal 2 for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module.

9.	If the circuit tests normal replace the G13 Generator.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

•	Refer to Generator Replacement (Diesel) Generator Replacement (LAU/A28NER) Generator Replacement (LLU/A16LET) Generator Replacement (LHU/A20NFT).

•	Control Module References for ECM replacement, setup, and programming