P1668

DTC P1668

Circuit Description
The engine control module (ECM) uses the generator turn-on signal circuit to control the voltage output of the generator. When a different voltage is desired, the ECM will change the pulse width modulation (PWM) signal to the voltage regulator via the generator turn-on signal circuit. This causes the voltage regulator to the voltage output of the generator. The ECM has fault detection circuitry which monitors the state of the generator turn-on signal circuit. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. The voltage regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the generator turn-on signal circuit, pulling the voltage low. This also causes the ECM to set the DTC.

DTC Descriptor
This diagnostic procedure supports the following DTC:

DTC P1668 Generator L-Terminal Control Circuit

Conditions for Running the DTC

Key ON Test
^ The key is in the ON position for 5 seconds.
^ The engine is OFF.

Engine Run Test
^ The engine is running.
^ The engine speed is less than 3,000 RPM.

Conditions for Setting the DTC

Key ON Test
^ The ECM detects a high signal voltage on the generator turn on signal circuit for at least 5 seconds.
^ The engine must be started.
During the RUN test, the ECM detects a low signal voltage on the generator turn on signal circuit for at least 5 seconds.

Action Taken When the DTC Sets
^ The ECM sends a class 2 message to the IPC to illuminate the charge indicator and/or turn on a message.
^ The ECM will not illuminate the malfunction indicator lamp (MIL).
^ The ECM will store the conditions present when the DTC set as Fail Records data only.

Conditions for Clearing the MIL/DTC

Step 1 - Step 10:

^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the scan tool Clear DTC Information function.