P1638

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

Schematic:

CIRCUIT DESCRIPTION
The generator has an input to the PCM called the F Terminal to indicate the percentage of total capacity that the generator is producing. This signal is detected by the PCM as a duty cycle from the generator and displayed on the scan tool as a percentage. The PCM can monitor the generators output under all conditions to determine if it is functioning normally.

When there is low demand from the electrical system on the generator, a low duty cycle percentage will be displayed. As more accessory load is placed on the generator, the duty cycle output detected by the PCM will approach 100 percent. A normally functioning generating system will never reach 100 percent as indicated on the scan tool.

CONDITIONS FOR RUNNING THE DTC
The engine is operating.

CONDITIONS FOR SETTING THE DTC
^ The F Terminal indicates a duty cycle less than 10 percent with the engine running.
^ All conditions met for 6 seconds.

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 DTC
^ A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
^ A history DTC will clear after 40 consecutive warm-up cycles, it no failures are reported by this or any other non-emission related diagnostic.
^ Use a scan tool in order to clear the DTC.

DIAGNOSTIC AIDS
^ DTCs P1637 and P1638 may set at the same time depending on the failure. Also, the L-terminal circuit can cause a DTC P1638 to set. This diagnostic table diagnoses both DTCs P1637 and P1638.
^ Use a scan tool in order to diagnosis the generator circuits. The scan tool should display Inactive for the L terminal and 10-40 percent for the F terminal when the ignition is ON. When the engine is operating, the display should indicate that the L terminal is Active and the F terminal is more than 10 percent.
^ A generator fault, such as a shorted output diode, malfunctioning regulator, open or shorted rotor, or open sense lead or battery feed may cause a low battery charge. Refer to Charging System Test in Starting and Charging for further information and generator diagnosis. Testing and Inspection
^ For an intermittent condition, refer to Symptoms. Symptom Related Diagnostic Procedures

TEST DESCRIPTION
The numbers below refer to the step numbers on the Diagnostic Table.
2. This step verifies the fault is current.
4. Inspect the circuit for an open or a short to ground if the test lamp did not illuminate.
5. If the scan tool displays Active, this indicates the circuit is open.
6. This step tests the F terminal for being shorted to a voltage. With the ignition ON, the F terminal should display between 10-40 percent. If the F terminal displays greater than 40 percent, inspect the circuit for a short to voltage.
7. When the engine is started the L terminal should be active.
8. This step is testing the L terminal for an open. If the L terminal displays Active when the circuit is grounded, this indicates the circuit is open.
10. This step is testing the F terminal circuit for an open or a short to ground. If the F terminal parameter goes to 99 percent the condition is within the generator.