Circuit Description
A dash light is illuminated by the powertrain control module (PCM) 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 is to supply the ground for the MIL circuit.
Conditions for Running the DTC
The ignition switch 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). |
or
| • | 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
| • | The PCM will turn the MIL off after 3 consecutive trips without a fault condition. |
| • | 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 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 in the connection at the PCM, the PCM may be malfunctioning; however, this is an extremely unlikely failure.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool Capture Info function to save the Freeze Frame and the Failure records for reference. The control module's data is deleted once the Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||
Does the lamp turn ON and OFF with each command? | -- | |||||||||
3 | The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If any additional DTCs are stored, refer to those table(s). Are any additional DTCs stored? | -- | Go to the applicable DTC table | Go to Diagnostic Aids | ||||||
4 |
Is the lamp OFF? | -- | ||||||||
5 |
Is the lamp ON? | -- | ||||||||
6 |
Did you perform a repair? | -- | ||||||||
7 | The MIL control circuit is shorted to ground. Repair as necessary. Refer to Wiring Repairs . Is the action complete? | -- | -- | |||||||
8 | Check the MIL circuit for the following:
Refer to Wiring Repairs . Is the repair complete? | -- | -- | |||||||
|
Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | ||||||||
10 |
Does the scan tool indicate the diagnostic Passed? | -- | ||||||||
11 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go the applicable DTC Table | System OK |
