Diagnostic Aids

WARNING: This page is about a different car, the 2005 Buick LaCrosse and 2005 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.

If any sensor using a 5-volt bias voltage, such as the intake air temperature (IAT) sensor or fuel sensor, is shorted to voltage, DTC P0651 may set in addition to DTC P0641.
For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections .

DTC P0641

Step	Action	Values	Yes	No
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module (PCM) Connector End Views
1	Did you perform the Diagnostic System Check - Vehicle?	-	Go to Step 2	Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2	Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition?	-	Go to Step 3	Go to Diagnostic Aids
3	Turn OFF the ignition. Disconnect the EGR valve. Turn ON the ignition, with the engine OFF. Command the EGR solenoid to 100 percent with a scan tool. Measure the voltage from the 5-volt reference circuit to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems. Is the voltage within the specified range?	4.8-5.2 V	Go to Step 5	Go to Step 4
4	Is the voltage measured in the previous step more than the specified value?	5.2 V	Go to Step 8	Go to Step 6
5	Connect the EGR valve. Disconnect a sensor associated with the same 5 volt reference Command the EGR solenoid to 100 percent with a scan tool. Measure the voltage from the 5-volt reference circuit to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems. Is the voltage within the specified range?	4.8-5.2 V	Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems	Go to Step 11
6	Monitor a DMM while disconnecting all other devices connected to the 5-volt reference circuit, one at a time. Refer to Engine Controls Component Views . If voltage changes when one of the devices are disconnected, replace the component. Was a component replaced?	-	Go to Step 13	Go to Step 7
7	Test this 5-volt reference circuit for a short to ground or any sensor low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	-	Go to Step 13	Go to Step 12
8	Monitor the DMM while disconnecting the a sensor assiduities with the 5 volt reference one at a time. Refer to Engine Controls Connector End Views . If the voltage returns to within the specified value when one of the devices is disconnected, test that sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	4.8-5.2 V	Go to Step 13	Go to Step 9
9	Test the 5-volt reference circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	-	Go to Step 13	Go to Step 10
10	Test for a short between the EGR 5-volt reference circuit and the EGR solenoid high control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	-	Go to Step 13	Go to Step 12
11	Replace the EGR valve. Refer to Exhaust Gas Recirculation (EGR) Valve Replacement . Did you complete the replacement?	-	Go to Step 13	-
12	Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement?	-	Go to Step 13	-
13	Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition?	-	Go to Step 2	Go to Step 14
14	Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed?	-	Go to Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information	System OK