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 instrument panel cluster (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
* 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.
Test
