P1638

DTC P1638 GENERATOR F-TERMINAL CIRCUIT









Circuit Description

This diagnostic DTC is used to monitor the field voltage of the generator. The generator is able to produce the desired voltage by varying the duty cycle of the field current. At low engine speeds, the field may have a duty cycle of 90%. At higher engine speeds and lower electrical loads, the duty cycle will be less. The generator produces a PWM signal that is monitored by the PCM on CKT 23 at connector C1 terminal 54. This signal duty cycle is sent to the PCM and if it tails below a certain duty cycle for too long, DTC P1638 will set.

Conditions for Running the DTC

^ Engine has been running for at least 60 seconds
^ Engine speed between 500 and 3000 RPM.

Conditions for Setting the DTC

Generator F-terminal duty cycle is 5% or less for 20 seconds.

Action Taken When the DTC Sets

^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ The PCM will command a message to be displayed.
^ The PCM may record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records.

Conditions for Clearing the Message/DTC

^ The PCM will turn the message OFF after one run and pass of the diagnostic test.
^ A History DTC will clear after forty consecutive warm-up cycles with no failures of any non-emission related diagnostic test.
^ A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
^ Use a scan tool to clear DTCs.
^ Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes. Reading and Clearing Diagnostic Trouble Codes

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

2. If DTC P0560 is also set, diagnose it first because the charging system may be faulty.
3. If the DTC is history, an intermittent wire problem may be present.
4. If the duty cycle is greater than 0%, the generator may be faulty.
5. If the duty cycle is greater than the failure threshold, the PCM may be faulty.