P1640

Circuit Description

The PCM contains chips called Output Driver Modules that provide 7 switchable ground outputs for operating solenoids, relays, telltales, and other devices. Each of these ground outputs has an internal fault line that feeds back to the PCM's microprocessor. Output Driver Module (ODM) # 1 can also sense high voltage coming in which might damage the chip. DTC P1640 is used to monitor ODM # 1's overvoltage sense line.

Conditions for Running the DTC

Engine running at least 10 seconds.

Conditions for Setting the DTC

Overvoltage is sensed for 2 seconds.

Action Taken When the DTC Sets

^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.

Conditions for Clearing the MIL/DTC

^ The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
^ A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
^ A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.
^ Use a scan tool to clear DTCs.
^ Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended.

Diagnostic Aids

Since an overvoltage at ODM # 1 should also trigger DTC P0563 the diagnosis for DTC P0563 may be used if vehicle voltage is actually too high.

A loose or faulty connection at generator L terminal may cause DTC P1640 to set intermittently.

Test Description

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

2. If ignition voltage and Instrument Panel Cluster (IPC) battery voltage are within 1.5 volt of each other, there may be a system voltage problem. If they are not within 1.5 volt of each other, find out why the PCM is different.
3. Checking if PCM ignition voltage is actually displaying system voltage.