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 P1668 : Generator L-Terminal Control CircuitDTC 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 |
|---|---|---|---|---|
Alternator L- Terminal Circuit | P2500 | P1668 | P2501 | P1668 |
Circuit/System Description
The engine control module (ECM) uses the alternator turn ON signal circuit to control the load of the alternator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the alternator turn ON signal circuit. The ECM should detect low voltage on alternator turn on signal 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 alternator turn on signal circuit. The ECM performs key ON and RUN tests to determine the status of the alternator turn on signal circuit.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
With the engine running, the ECM detects low/high compared to a predetermined voltage on the alternator turn on signal circuit for at least 15 seconds.
Action Taken when the DTC Sets
DTCs P1668, P2500 or P2501 are type C store only DTCs.
Conditions for Clearing the MIL/DTC
DTCs P1668, P2500 or P2501 are type C store only DTCs.
Reference Information
Schematic Reference
Starting and Charging Schematics
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
- With ignition ON and the engine OFF, disconnect the alternator harness at the alternator and measure the voltage of the alternator turn on signal circuit should read near 0 volts.
- With ignition ON and the engine running, the voltage of the alternator turn on signal circuit should read over 3.5 volts.
- If all circuits test normal Refer to Charging System Test .
| ⇒ | If greater than 0 volts test the alternator turn on signal circuit for a short to voltage. If circuit test normal replace the ECM. |
| ⇒ | If no voltage is measured, test the alternator turn on signal circuit for a short to ground an open/high resistance If circuit tests normal replace the ECM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
