P1660

Circuit Description

The PCM contains a chip called a Quad Driver Module that provides 4 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 PCMs microprocessor. When the output is OFF, the quad driver should receive the 12 volts fed to the solenoid, relay, etc. When the output is ON, the quad driver should receive 0 volt since it is grounding the output. If it receives 0 volt when the output is OFF or 12 volts when the output is ON, it sets the fault line low. DTC P1660 is used to monitor the fault line of the cooling fan control relay output.

Conditions for Running the DTC

^ Ignition voltage between 10 and 16 volts.
^ PCM in Closed Loop fuel control.
^ Engine running for at least 10 seconds.

Conditions for Setting the DTC

Fault line is low 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

Review the Freeze Frame and Failure Records that were stored when this DTC set. Check these conditions to determine the odometer reading and driving conditions under which this DTC set.