For 1990-2009 cars

### 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 L-Terminal Circuit

### Circuit Description

The engine control module (ECM) 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 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 key is in the RUN position, with the engine OFF, the ECM should detect a duty cycle that is near 0 percent. However, when the engine is running, the duty cycle should be between 5-95 percent.

### Conditions for Running the DTC

• | Vehicle speed is greater 8 km/h (5 mph).

• | System voltage between 9.5-18 volts.

### Conditions for Setting the DTC

During the Ignition Key ON Test, the ECM detects a PWM signal greater than 65 percent for at least 5 seconds. Or during the RUN test, the ECM detects a PWM signal less than 5 percent for at least 15 seconds.

### Action Taken When the DTC Sets

• | The ECM will command the charge indicator and/or warning message to be illuminated on the instrument panel cluster (IPC) and the driver information center (DIC) (if equipped).

• | The ECM will not illuminate the malfunction indicator lamp (MIL).

• | The ECM will only store the operating conditions as Failure Records data when setting the DTC.

### Conditions for Clearing the MIL/DTC

• | The engine will command the message OFF after the diagnostic test has been run and passed once.

• | 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.

### Reference Information

#### Schematic Reference

Starting and Charging Schematics

#### Connector End View Reference

Engine Electrical Connector End Views

#### Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

#### Scan Tool Reference

Scan Tool Data List

Scan Tool Data Definitions

### Circuit/System Verification

Turn on the ignition switch and start the engine with an installed scan tool. Observe the Generator F-Terminal Signal parameter in the ECM data list, which should be between 5-95 percent.

### Circuit/System Testing

1. Turn OFF the ignition. Disconnect the generator harness connector.
2. Turn on the ignition switch. Turn off the engine. Connect the test lamp to the battery positive terminal and repeatedly probe the generator field duty cycle signal circuit (harness side), then monitor the Generator F-Terminal Signal parameter in the data list, and its values will change from 0 percent to above 95 percent.

⇒ | If the Generator F-Terminal Signal parameter is unaffected by the test lamp, test the Generator F-Terminal signal circuit for a short to ground, a high resistance or an open. If the circuit testing is normal, replace the ECM.

3. Go to Charging System Test.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Refer to Control Module References for ECM replacement, setup, and programming.