P1637

Circuit Description
The L-terminal circuit from the generator is a discrete circuit into the PCM. The PCM supplies the ignition voltage to the generator lamp feed. This ignition voltage is pulled low by the generator once the ignition switch supplies ignition 1 voltage. The voltage stays low until the generator turns. When the generator is up and running, the PCM detects ignition voltage. Therefore, with no failures with the vehicle's charging system, the lamp terminal circuit will go low (0 volts) when the ignition switch is powered up and then goes to the ignition voltage after the engine is started. When the charging system detects a fault (circuit shorted to ground), the Instrument Panel Cluster (IPC) displays a message.

Conditions for Running the DTC
Engine operating.

Conditions for Setting the DTC
The PCM detects an improper voltage on the generator L terminal circuit.

Action Taken When the DTC Sets
^ The PCM stores the DTC information into memory when the diagnostic runs and fails.
^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

Conditions for Clearing the MIL/DTC
^ A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
^ A last test failed (Current DTC) will clear when the diagnostic runs and does not fail.
^ Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

^ The following may cause an intermittent:
- Poor connections: Check for adequate terminal tension.
- Corrosion.
- Mis-routed harness.
- Rubbed through wire insulation.
- Broken wire inside the insulation.
^ For an intermittent, refer to Symptoms.
^ A generator fault, such as a shorted output diode, malfunctioning regulator, open or shorted rotor may cause a low battery charge.
^ Use a scan tool in order to diagnosis the generator circuits. A scan tool displays Generator L-Terminal Inactive when there is a problem with the L-terminal circuit. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
2. This step determines if a fault is present.
11. A poor connection at the generator causes no output.