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.
Conditions for Running the DTC
| • | Ignition switch in the on position (test 1). |
or
| • | Engine operating (test 2). |
Conditions for Setting the DTC
| • | Voltage on MIL control circuit high (near battery volts) (test
1). |
| • | All diagnostic set conditions met for 2 seconds. |
or
| • | All diagnostic set conditions met for 2 seconds (test 2). |
| • | Voltage on MIL control circuit 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 stores in the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | A History DTC clears after forty consecutive warm-up cycles,
if this or any other emission related diagnostic does not report any failures. |
Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the
PCM. Inspect the PCM connector gaskets when diagnosing/replacing the
PCM. Ensure that the gaskets are installed correctly. The gaskets prevent
water intrusion into the PCM.
A faulty bulb, the control circuit shorted to ground or battery voltage,
will cause a P1641 to set.
An intermittent can be caused by the following:
| • | Rubbed through wire insulation |
| • | Broken wire inside the insulation |
