P0620

Schematic:

CIRCUIT DESCRIPTION

The Powertrain Control Module (PCM) output (L) terminal to the alternator determines when the alternator will be turned off. The alternator is on under all normal vehicle operating conditions except during low RPM conditions. The alternator is turned off during low RPM conditions in order to remove excess load from the engine.

The PCM input field (F) terminal from the alternator provides a 400 Hz Pulse-width Modulated (PWM) signal to the PCM. The duty cycle of the F terminal mimics the duty cycle of the field coils in the alternator, Thus, the F terminal duty cycle indicates the relative electrical load on the alternator.

The alternator telltale lamp will illuminate any time the ignition is on and the engine is not running. The telltale will turn off after the engine is running and the alternator is putting out the desired amperage.

CONDITIONS FOR RUNNING THE DTC
^ The engine is running.
^ The voltage telltale is on.

CONDITIONS FOR SETTING THE DTC
^ The L terminal voltage is low while the PCM is commanding the generator on.
^ The above condition is present for more than 30 seconds.
OR
^ The F terminal PWM is less than 5 percent.
^ The engine RPM is less than 2500.
^ The above conditions are present for more than 30 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will not illuminate the Malfunction Indicator Lamp (MIL).
^ The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ DTC can be cleared by using the scan tool.

DIAGNOSTIC AIDS
Check for the following conditions:
^ A faulty connection at the PCM or the generator. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connections. Use a corresponding mating terminal to test for the proper terminal tension. Refer to Testing for Intermittent and Poor Connections in Diagrams.
^ Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM, turn the ignition on, and observe a voltmeter connected to the generator circuits at the PCM harness connector while moving the connectors and wiring harnesses related to the generator control circuit. A change in voltage will indicate the location of the fault. Refer to Testing for Intermittent and Poor Connections in diagrams.


TEST DESCRIPTION

Diagnostic Chart:

The numbers below refer to the step numbers on the diagnostic table.
10. This vehicle is equipped with a PCM which utilizes an electrically Erasable Programmable Read-only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.