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

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1996 🢒 GMC Suburban - 2WD 🢒 Engine 🢒 Engine Controls - 6.5L 🢒 DTC P1641 Malfunction Indicator Lamp (MIL) Control Circuit

Circuit Description

A dash light is illuminated by the PCM if diagnostics have detected certain errors related to the engine performance or engine sensor status. When the PCM is commanding the 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 battery volts). The primary function of the PCM is to supply the ground for the MIL circuit. This is a type D DTC

Conditions for Setting the DTC

•	MIL requested ON.

•	Voltage on MIL control circuit high (near battery volts).

•	MIL requested OFF.

•	Voltage on MIL control circuit low (near 0 volts).

Action Taken When the DTC Sets

Will not turn ON the MIL.

Conditions for Clearing the MIL/DTC

•	A History DTC will clear when forty consecutive warm-up cycles that the diagnostic does not fail (coolant temperature has risen 5°C (40°F) from start up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle.

•	Use of a Scan tool

Diagnostic Aids

A faulty bulb or the control circuit shorted to ground will cause a P1641 to set.

Test Description

Number(s) below refer to the Step number(s) on the Diagnostic Table.

Be sure that both the ON and the OFF states are commanded. Repeat the commands as many times as necessary.

If no trouble is found in the control circuit or the connection at the PCM, the PCM maybe faulty, however, this is an extremely unlikely failure.

Step

Action

Value(s)

Yes

Important: Before clearing DTCs use the scan tool to record freeze frame and failure records for reference, as data will be lost when Clear Info function is used.

Was the On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Ignition ON, engine OFF.
Using a scan tool, command the lamp ON and OFF.

Does the lamp turn ON and OFF with each command?

Go to Step 3

Go to Step 4

DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs were stored refer to those table(s).

Are additional DTCs stored?

Go to the applicable DTC table

Go to Diagnostic Aids

Ignition OFF.
Disconnect the PCM connector containing the lamp control circuit.
Ignition ON, engine OFF.

Is the lamp OFF?

Go to Step 5

Go to Step 7

Ignition ON, 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 PCM.
If a problem was found, repair as necessary.

Was a repair performed?

Go to Step 10

Go to Step 9

MIL control circuit is shorted to ground, repair as necessary.

Is the action complete?

Go to Step 10

Check the MIL circuit for the following:

•	Open ignition feed to the bulb.

•	Faulty bulb.

•	Control circuit open or shorted to B+.

Is the repair complete?

Go to Step 10

Replace the faulty PCM.

Important: If the PCM is faulty, the new PCM must be programmed.

Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

Go to Step 10

Using the Scan Tool, select DTC, Clear Info.
Start engine and idle at normal operating temperature.
Select DTC, Specific, then enter the DTC number which was set.
Operate vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the Scan Tool indicate that this diagnostic Ran and Passed?

Go to Step 11

Go to Step 2

Using the Scan Tool, select Capture Info, Review Info.

Are any DTCs displayed that have not been diagnosed?

Go the Applicable DTC Table

System OK