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DTC P0621, P2500, or P2501

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 Descriptors

DTC P0621: Generator L-Terminal Circuit

DTC P2500: Generator L-Terminal Circuit Low Voltage

DTC P2501: Generator L-Terminal Circuit High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

B+

P0622, P0625

P0622, P0625

-

-

Signal

P0622, P0625

P0622, P0625

P0622, P0626

-

Control

P0621, P2500

P0621, P2500

P0621, P2501

-

Circuit/System Description

The engine control module (ECM) uses the generator turn on control circuit, or L-terminal circuit, to control the load of the generator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This controls the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the generator turn ON control circuit. The ECM should detect low voltage on generator turn on control circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect high voltage on the generator turn on control circuit. The ECM performs tests to determine the status of the generator turn on control circuit.

Conditions for Running the DTC

P0621

    • The ignition is ON, engine OFF for ignition on test.
    • The engine is running for the run test.

P2500

The engine is running.

P2501

    • The ignition is ON.
    • The engine is OFF.

Conditions for Setting the DTC

P0621

    • During the ignition on test, the ECM detects voltage on the alternator turn on control circuit for 5 s.
    • During the run test, the ECM detects low voltage on the generator turn on control circuit for 15 s.

P2500

The ECM detects low voltage on the generator turn on control circuit for 2 s.

P2501

The ECM detects high voltage on the alternator turn on control circuit for 2 s.

Action Taken When the DTC Sets

P0621

DTC P0621 is a C type DTC.

P2500 and P2501

The charge indicator turns ON 15 s after the DTC sets.

Conditions for Clearing the DTC

P0621

DTC P0621 is a C type DTC.

P2500 and P2501

    • The DTC will pass when the conditions for setting the DTC are no longer met for 2 s.
    • A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The charge indicator turns OFF 15 s after the DTC passes.

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 Testing
  1. Verify that a test lamp illuminates between the alternator B+ circuit terminal A X1 and earth.
    2. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  2. Ignition OFF, disconnect the X2 harness connector at the G13 Generator.
  3. Ignition ON, test for less than 1 V between the control circuit terminal 1 and ground.
    4. ⇒If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module.
  4. Engine running, test for greater than 3 V between the control circuit terminal 1 and ground.
    5. ⇒ If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module.
  5. If all circuits test normal, test or replace the G13 Alternator.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Generator Replacement : 2.4L LAF → 1.8L 2H0 → 2.0L Diesel LNP
    • Control Module References for ECM replacement, setup, and programming
   


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