Circuit Description
A malfunction indicator lamp (MIL) lamp is illuminated by the powertrain control module (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 voltage). The primary function of the PCM 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 voltage on MIL control circuit is high (near battery voltage) when the MIL is requested ON.
or
Voltage on MIL control circuit is low (near 0 volts) when the MIL is requested OFF.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
A faulty bulb, the control circuit shorted to ground, or battery voltage, will cause a DTC P1641 to set.
An intermittent can be caused by the following conditions:
| • | 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.
-
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 malfunctioning, however, this is an extremely unlikely failure.
Step | Action | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |||||||
Does the lamp illuminate with each command? | Go to Step 3 | Go to Step 4 | |||||||
3 | The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs were stored, refer to those tables. Are any additional DTCs stored? | Go to Diagnostic Aids | |||||||
4 |
Does the lamp illuminate? | Go to Step 7 | Go to Step 5 | ||||||
5 |
Does the lamp illuminate? | Go to Step 6 | Go to Step 8 | ||||||
6 |
Did you find and correct the condition? | Go to Step 10 | Go to Step 9 | ||||||
7 | Repair the short to ground in the MIL control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 10 | -- | ||||||
8 | Check the MIL circuit for the following:
Did you complete the repair? | Go to Step 10 | -- | ||||||
Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 10 | -- | |||||||
10 |
Does the DTC run and pass? | Go to Step 11 | Go to Step 2 | ||||||
11 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |||||||
