Test Procedure
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2005 Mercury Sable, 2005 Mercury Mountaineer, 2005 Mercury Monterey, 2005 Mercury Montego, and 2005 Mercury Mariner. However, it is still accessible from the selected car via links, so may be relevant.
- NB1 MALFUNCTION INDICATOR LAMP ALWAYS ON (NO DTCS PRESENT)
Does the vehicle start?
Yes No GO to NB2. Concern is elsewhere. RETURN to SYMPTOM CHARTS - GASOLINE MODELS for further direction. - NB2 CHECK THE MIL CIRCUIT FOR A SHORT TO GROUND IN THE HARNESS
- Key in OFF position.
- PCM connector disconnected.
- Measure the resistance between:
(+) PCM Connector, Harness Side (-) Vehicle Battery MIL Negative terminal
Is the resistance greater than 10K ohms?
Yes No INSTALL a new PCM. REFER to FLASH ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY (EEPROM) . REPAIR the short circuit to GND. - NB3 MALFUNCTION INDICATOR LAMP (MIL) NEVER ON
Does the vehicle start?
Yes No GO to NB4. Concern is elsewhere. RETURN to SYMPTOM CHARTS - GASOLINE MODELS for further direction. - NB4 MIL HARNESS CHECK
- Key in OFF position.
- PCM connector disconnected.
- Key in ON position.
- Connect a 5 amp fused jumper wire between the following:
Point A PCM Connector, Harness Side Point B MIL Ground - Remove the jumper wire(s)
Does the MIL Illuminate when grounded?
Yes No INSTALL a new PCM. REFER to FLASH ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY (EEPROM) . GO to NB5. - NB5 CHECK FOR AN OPEN MIL CIRCUIT BETWEEN THE PCM AND INSTRUMENT CLUSTER
- Key in OFF position.
- Disconnect the instrument cluster.
- Measure the resistance between:
(+) PCM Connector, Harness Side (-) IC Connector, Harness Side MIL MIL
Is the resistance less than 5 ohms?
Yes No REFER to INSTRUMENT CLUSTER to diagnose the MIL and its circuitry. REPAIR the open circuit.
VERIFY the repair by turning the key to the ON position.