DTC P1641 Malfunction Indicator Lamp (MIL) Control Circuit. GMC Truck Savana 2000

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2000 🢒 Savana 🢒 Engine 🢒 Engine Controls - 6.5L (L65) 🢒 DTC P1641 Malfunction Indicator Lamp (MIL) Control Circuit

Engine Controls Components
Fuses, MIL, PCM, DLC, G101, G103, G201
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

A dash light is illuminated by the powertrain control module (PCM) when the ignition is ON with the engine OFF, or if the diagnostics have detected certain errors related to the engine performance or the engine sensor status. When the PCM is commanding the malfunction indicator lamp (MIL) ON, the voltage potential of the circuit will be low, near 0 volts. When the PCM is commanding the MIL OFF, the voltage potential of the circuit will be high, near the battery volts. The primary function of the PCM in this circuit is to supply the ground for the MIL circuit.

Conditions for Running the DTC

The ignition is in the ON position.

Conditions for Setting the DTC

•	The MIL is requested ON.

•	The voltage on the MIL control circuit is high (near the battery volts).

•	The MIL is requested OFF.

•	The voltage on the MIL control circuit is low (near 0 volts).

Action Taken When the DTC Sets

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

•	The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Failure Records.

Conditions for Clearing the MIL/DTC

•	A history DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.

•	The scan tool Clear Info function was used.

Diagnostic Aids

A malfunctioning bulb, the control circuit shorted to ground or battery voltage, will cause a P1641 to set.

An intermittent may be caused by the following:

•	Poor connections

•	Rubbed through wire insulation

•	Broken wire inside the insulation

Test Description

The numbers below refer to the step numbers on the diagnostic table:

Ensures that both the ON and the OFF states are commanded.

This step ensures that the replacement PCM, which utilizes an electrically erasable programmable read only memory (EEPROM), is programmed when installed. If no trouble is found in the control circuit or in the connection at the PCM, the PCM may be malfunctioning, however, this is an extremely unlikely failure.

Step

Action

Values

Yes

Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The data in the control module is deleted once the Clear Info function is used.

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Turn ON the ignition with the engine OFF.

Important: Ensure that both the ON and the OFF states are commanded. Repeat the commands as many times as necessary.

Use a scan tool in order to command the lamp ON and OFF.

Does the lamp turn ON and OFF with each command?

Go to Step 3

Go to Step 4

The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If any additional DTCs are stored, refer to those tables.

Are any additional DTCs stored?

Go to the applicable DTC table

Go to Diagnostic Aids

Turn OFF the ignition.
Disconnect the PCM connector containing the lamp control circuit.
Turn ON the ignition with the engine OFF.

Is the lamp OFF?

Go to Step 5

Go to Step 7

Turn ON the ignition with the engine OFF.
With a fused jumper wire connected to ground, probe the lamp control circuit in the PCM harness connector.

Is the lamp ON?

Go to Step 6

Go to Step 8

Check for poor connections at the PCM.
If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you perform a repair?

Go to Step 10

Go to Step 9

Inspect the MIL control circuit for a short to ground.
Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 10

Check the MIL circuit for the following conditions:

•	A malfunctioning bulb

•	A control circuit either open or shorted to B+

Repair the conditions as needed. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

Go to Step 10

Important: The new PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

Go to Step 10

Use the scan tool in order to clear the DTCs.
Start the engine.
Allow the engine to idle until the engine reaches the normal operating temperature.
Select DTC and the Specific DTC function.
Enter the DTC number that was set.
Operate the vehicle within the Conditions for Setting this DTC until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

Go to Step 11

Go to Step 2

Does the scan tool display any additional undiagnosed DTCs?

Go the applicable DTC table

System OK