Test Procedure

WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 2004 Mercury Sable, 2004 Mercury Mountaineer, 2004 Mercury Monterey, 2004 Mercury Marauder, and 2004 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.

TJ1 DTCS P0720, P0721, P0722, P0723 AND P1900: VERIFY DRIVE CYCLE

Access the PCM -OSS PID.
Drive the vehicle.
Monitor the PID in all transmission gear ranges while increasing and decreasing the speed.

Does the PID reading increase and decrease with engine and vehicle speed?

Yes	No
OSS performed as expected GO to TJ2.	KEY OFF GO to TJ3.

TJ2 VISUAL INSPECTION

OSS connector disconnected.
INSPECT the OSS harness for damage.
INSPECT the OSS vehicle harness connector for damage and proper seating.
If possible, carry out a wiggle test.

Have any problems been found?

Yes	No
REPAIR FAULT	GO to Z1.

TJ3 VERIFY THE TYPE OF OSS SENSOR

INSPECT for a Hall-effect or VR-type OSS sensor.

Is this a Hall-effect type OSS sensor?

Yes	No
GO to TJ4.	GO to TJ6.

TJ4 CHECK THE VPWR TO THE OSS SENSOR

OSS connector disconnected.
Key ON Engine OFF.
Measure the voltage between:

( + )OSS Connector, Harness Side	( - )Vehicle battery
VPWR	Negative terminal

Is the voltage greater than 10.5 V?

Yes	No
KEY OFF GO to TJ5.	KEY OFF REPAIR the open circuit.

TJ5 CHECK THE VPWR GROUND TO THE OSS SENSOR

Measure the resistance between:

( + )OSS Connector, Harness Side	( - )Vehicle battery
PWRGND	Negative terminal

Is the resistance less than 5 ohms?

Yes	No
GO to TJ6.	REPAIR the open circuit.

TJ6 CHECK THE OSS CIRCUIT FOR A SHORT TO VREF AND VPWR IN THE HARNESS

Key ON Engine OFF.
OSS connector disconnected.
Measure the voltage between:

( + )OSS Connector, Harness Side	( - )Vehicle battery
OSS	Negative terminal

Is the voltage less than 1 V?

Yes	No
KEY OFF GO to TJ7.	KEY OFF REPAIR the short circuit.

TJ7 CHECK THE OSS CIRCUIT FOR AN OPEN IN THE HARNESS

PCM connector disconnected.
OSS connector disconnected.
Measure the resistance between:

( + )PCM Connector, Harness Side	( - )OSS Connector, Harness Side
OSS - Pin 84	OSS
SIGRTN - Pin 91	SIGRTN

NOTE: Hall-effect sensors are not equipped with a SIGRTN circuit.

Are the resistances less than 5 ohms?

Yes	No
GO to TJ8.	REPAIR the open circuit.

TJ8 CHECK THE OSS CIRCUIT FOR A SHORT TO GROUND IN THE HARNESS

Measure the resistance between:

( + )OSS Connector, Harness Side	( - )OSS Connector, Harness Side
OSS	PWRGND
OSS	SIGRTN

Measure the resistance between:

( + )OSS Connector, Harness Side	( - )
OSS	Ground

Are the resistances greater than 10 KOhm??

Yes	No
GO to TJ9.	REPAIR the short circuit.

TJ9 VERIFY THE TYPE OF OSS SENSOR

INSPECT for a Hall-effect or VR-type OSS sensor.

Is this a Hall-effect type OSS sensor?

Yes	No
GO to TJ10.	GO to TJ11.

TJ10 CHECK THE OSS SIGNAL OUTPUT TO THE PCM, HALL-EFFECT TYPE SENSOR

PCM connector disconnected.
Raise the vehicle to allow rotation of the front drive wheels.
Key ON Engine OFF.
Transmission in NEUTRAL.
Measure the voltage between:

( + )PCM Connector, Harness Side	( - )PCM Connector, Harness Side
OSS - Pin 84	PWRGND - Pin 103

NOTE: The opposite wheel must be held stationary.
The voltage should rise above 5 volts and fall below 1 volt in a regular cycle. Observe several cycles.

Does the OSS output voltage rise and fall as specified?

Yes	No
REPLACE the PCM. REFER to FLASH ELECTRICALLY ERASEABLE PROGRAMMABLE READ ONLY MEMORY - FLASH EEPROM .	REPLACE the OSS sensor.

TJ11 CHECK THE RESISTANCE OF THE OSS SENSOR

Measure the resistance between:

( + )OSS Connector, Component Side	( - )OSS Connector, Component Side
OSS	SIGRTN

Is the resistance between 400 ohms - 1.25K ohms?

Yes	No
REPLACE the PCM. REFER to FLASH ELECTRICALLY ERASEABLE PROGRAMMABLE READ ONLY MEMORY - FLASH EEPROM .	REPLACE the OSS.