Cat Monitor Will Not Complete

Rob Mechanic California Posted   Latest  
Unsolved
Emissions
2008 Ford Crown Victoria 4.6L (V) 4-spd (4R75E) — 2FAFP71V88X161367
Unable To Complete Cat Monitor

the cat monitor will not run, all other monitors have run. in mode 6 the switch ratio from front to rear and rear to front indicate 0, i disconnected the battery and tried to re run the monitors and the cat did not complete. the o2 sensors are working as expected. i am at a loss as to what to do next. i checked if the pcm has an update but it has the latest calibration. any suggestions? Thank You for your time.

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Glenn Owner/Technician
Texas
Glenn
 

I recommend you inspect all harness and test the individual O2 sensors. There could be a bad heater in one of them not showing resistance. The PCM monitors the heater circuits.

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Paul Mechanic
Illinois
Paul
 

What does mode 6 show for cats when codes are cleared. How are fuel trims? Can you check local epa emissions for past test results to make certain cat monitor set to ready? Maybe look up criteria for setting P0430 and P0420 to check when pcm checks cats. Fords are pretty quick to set unless something is not right, like trims or temp.

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Stephen Educator
Ohio
Stephen
 

Graph out your front and rear O2 sensors and compare them. Also, snap the throttle several times while monitoring the rear O2 sensor. It should change considerably. If not, the rear Os sensor may be your problem.

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Timothy Owner/Technician
Wisconsin
Timothy
 

The switch ratio will not update in Mode 6 until the cat monitor clears, which is why it shows zero. You can do some graphing and math of your own to see what the switch ratio is…likely, the cats are dead…pretty common on an old beast with original cats.

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Robert Diagnostician
California
Robert
 

Of all the cars I have had that would not run the cat monitor I would say replacing the O2 sensors fixed the problem almost every time. When it did not the graphing of the O2 sensors showed the cats as slow to warm up and marginal. One thing to make sure of is the operational parameters of the cat monitor. The engine not quite getting up to temp but not bad enough to set a thermostat code is…

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Stephen Owner/Technician
California
Stephen
 

Check for proper engine temp. I've seen if the thermostat sticks open a bit, the engine will not get hot enough to light off the cats

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Timothy Owner/Technician
Wisconsin
Timothy
 

Stephen: engine temp has little to nothing to do with the catalyst ‘lighting off’. The cats come on-line in about 90 seconds when driving (not in the stall), long before engine temp comes up, and catalyst light-off, in late model vehicles, comes on even more rapidly. There are catalyst heating strategies on newer vehicles to assure that happens. OBD 2 regs say that the engine has to be in fuel…

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Thomas Technician
California
Thomas
 

Stuck open thermostat will keep cat monitor from running especially on gm ,cleared the monitor on hundreds of cars by replacing the stat​.​needs to see above 190 at cruise

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Ray Diagnostician
California
Ray
 

Scope the O2 sensors and post them here. Make sure there are no exhaust leaks, If you do Smog checks, use your five gas analyzer to do Cat efficiency tests.

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Paul Technician
California
Paul
 

Hi Robb, Proper engine temp, O2 heaters and having a minimum amount of fuel in the tank are things to check. Ford likes to see a minimum of ¼ tank of fuel, I try to keep them at ½ Full to be safe. Also, if you have on O2 sensor or O2 heater that is right on the edge of failing, the pcm may be wanting to see several good trips on the sensor or heater to make sure it will pass before passing the…

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Chris Technical Support Specialist
New York
Chris
 

Also check your temperature sensors for rationality Biased but not out enough to trigger a DTC can cause certain monitors not to run. I have also experienced cat monitors not setting, even with a passed evap, no DTCs with FTP voltage over 4.0V KOEO. This is out of range as it should be about 2.6V static pressure. If you have the availability to check the PCM calibration, Per the website it…

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Rudy Technician
California
Rudy
 

Robb- what drive cycle are you running? Where did you get that info?

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Darren Mechanic
Wisconsin
Darren
 

Aftermarket software?

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Ray Diagnostician
California
Ray
 

youtube​.​com/watch?v=uVmWwK… Good video on Oxygen storage capacity testing if you have a scope.

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Jim Educator
California
Jim
   

Robb Would it help to visit Ford's free OBDII theory and operation web page? Do you find anything of value here? motorcraftservice​.​com/FreeResources…

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