DTC P1641 Malfunction Indicator Lamp (MIL) Control Circuit. Buick Century 1997

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1997 🢒 Century 🢒 Engine 🢒 Engine Controls - 3.1L 🢒 DTC P1641 Malfunction Indicator Lamp (MIL) Control Circuit

Engine Controls Components
Power, Ground, MIL, DLC
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

Output Driver Modules (ODMs) are used by the PCM to turn on many of the current-driven devices that are needed to control various engine and Transaxle functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which the PCM is commanding on.

Unlike the Quad Driver Modules (QDMs) used in prior model years, ODMs have the capability of diagnosing each output circuit individually. DTC P1641 set indicates an improper voltage level has been detected on ODM A output 1, which controls the Malfunction Indicator Lamp (MIL).

Conditions for Setting the DTC

•	Ignition is on.

•	An improper voltage level has been detected on the MIL driver circuit.

•	Above conditions for at least 20 seconds.

Action Taken When the DTC Sets

•	The PCM will not illuminate the malfunction indicator lamp (MIL).

•	The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

Conditions for Clearing the MIL/DTC

•	A 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 Info function.

Diagnostic Aids

Check for the following conditions:

•	Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

•

Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM, turn the ignition on and observe a voltmeter connected to the MIL driver circuit at the PCM harness connector while moving connectors and wiring harnesses related to the MIL. A change in voltage will indicate the location of the fault.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

Normally, ignition feed voltage present on the output driver circuit with the PCM disconnected and the ignition turned on.

Checks for a shorted component or a short to battery positive voltage on the output driver circuit. Either condition would result in a measured current of over 1.5 amps. Also checks for a component that is going open while being operated, resulting in a measured current of 0.0 amps.

Checks for a faulty MIL bulb.

This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Step	Action	Value(s)	Yes	No
1	Was the Powertrain On Board Diagnostic (OBD) System Check performed?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Turn the ignition off, disconnect the PCM. Turn the ignition on. Using DMM (J 39200), measure voltage between the MIL output driver circuit at the PCM harness connector and ground. Is voltage near the specified value?	B+	Go to Step 3	Go to Step 6
3	Set up the DMM to measure 10 amp range. Measure current between the MIL output driver circuit and ground. Monitor the current reading on the Digital MultiMeter for at least 2 minutes. Does the current reading remain between the specified values?	0.05 amp - 1.5 amps	Go to Step 11	Go to Step 4
4	Turn the ignition off, disconnect the instrument panel (leave the PCM disconnected). Turn the ignition on. Using the DMM, measure voltage between the MIL output driver circuit and ground. Is the voltage at the specified value?	0.0 V	Go to Step 10	Go to Step 5
5	Locate and repair short to voltage in the MIL output driver circuit. Refer to Repair Procedures in Electrical Diagnosis. Is the action complete?	--	Go to Step 15	--
6	Check the ignition feed fuse for the instrument panel indicators. Is the fuse blown?	--	Go to Step 7	Go to Step 8
7	Locate and repair short to ground in ignition feed circuit for the instrument panel indicators. Refer to Repair Procedures in Electrical Diagnosis. Replace the fuse. Is the action complete?	--	Go to Step 15	--
8	Disconnect the instrument cluster. Ignition on, measure voltage between the ignition feed circuit for the instrument cluster indicators and ground. Is voltage near the specified value?	B+	Go to Step 9	Go to Step 13
9	Check the MIL output driver circuit for an open or a short to ground. If a problem is found, repair the MIL output driver circuit. Refer to Repair Procedures in Electrical Diagnosis. Was a problem found?	--	Go to Step 15	Go to Step 10
10	Check the MIL output driver circuit and the instrument panel indicators ignition feed circuit for a poor connection at the instrument panel and at the PCM. If a problem is found, replace faulty terminal(s). Was a problem found?	--	Go to Step 15	Go to Instrument Panel in Electrical Diagnosis
11	Turn the ignition off, reconnect the PCM and disconnect the instrument cluster. Turn the Ignition on, connect J 34142-B test light between the MIL output driver circuit and the ignition feed circuit at the instrument panel harness connector. Using the scan tool outputs test function, cycle the MIL on and off. Does the test light flash on and off?	--	Go to Diagnostic Aids	Go to Step 12
12	Check the MIL output driver circuit for a poor connection at the PCM. If a problem is found, replace faulty terminal. Refer to Repair Procedures in Electrical Diagnosis. Was a problem found?	--	Go to Step 15	Go to Step 14
13	Locate and repair open in ignition feed circuit to the I/P indicator. Refer to Repair Procedures in Electrical Diagnosis. Is the action complete?	--	Go to Step 15	--
14	Replace the PCM. Important: : Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is the action complete?	--	Go to Step 15	--
15	Review and record scan tool Fail Records data. Clear the DTC(s). Operate vehicle within Fail Records conditions as noted. Using a scan tool, monitor SPECIFIC DTC info for DTC P1641 until the DTC P1641 test runs. Does scan tool indicate DTC P1641 failed this ignition?	--	Go to Step 2	Repair complete