Conditions for Clearing the MIL/DTC

WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.

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.

DTC P1668

Step	Action	Value	Yes	No
Schematic Reference: Engine Controls Schematics for the 3.9L (LZ9) engine or Starting and Charging Schematics Connector End View Reference: Engine Control Module (ECM) Connector End Views for the 3.9L (LZ9) engine
1	Did you perform the Diagnostic System Check - Vehicle?	-	Go to Step 2	Go to Diagnostic System Check - Vehicle
2	Install a scan tool. Turn ON the ignition, with the engine OFF. Wait 5 seconds. Start the engine. With a scan tool, monitor the DTC information for DTC P1668 in Engine Controls. Does the scan tool indicate that DTC P1668 has passed?	-	Go to Testing for Intermittent Conditions and Poor Connections	Go to Step 3
3	Turn OFF the engine. Disconnect the generator harness connector. Start the engine. With a DMM measure the pulse width modulation (PWM) signal between the generator turn on signal circuit and ground. Is the PWM signal within the specified value?	15-87%	Go to Step 5	Go to Step 4
4	Test the generator turn on signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition?	-	Go to Step 10	Go to Step 7
5	Test the generator battery positive voltage output circuit for a high resistance or open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition?	-	Go to Step 10	Go to Step 6
6	Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs . Did you find and correct the condition?	-	Go to Step 10	Go to Step 8
7	Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition?	-	Go to Step 10	Go to Step 9
8	Replace the generator. Refer to Generator Replacement (LX9) or Generator Replacement (LZ9) . Did you complete the replacement?	-	Go to Step 10	-
9	Replace the ECM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement?	-	Go to Step 10	-
10	Use the scan tool in order to clear the DTCs. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text. Does the DTC reset?	-	Go to Step 3	System OK