P1641

Diagnostic Chart:

Schematic:

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).

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
^ 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:
2. Ensures that both the ON and the OFF states are commanded.
9. 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.