98 ford f150 4.6 ltr . replaced alternator 2 months ago . by disconnecting the battery the obd11 sensors cleared . after doing the drive cycle , the o2 and hrt sensors will not reset . i have run a can of bg 44k platinum thru the system and still can't get the sluggish o2 and hrt sensor to reset for smog test in california . any ideas ? smog center want $125 for dynamometer test to diagnose .

 

You may need new O2 sensors.

 

thanks . much appreciated . i have 128k miles on the vehicle and have the original sensors.

 

I change my o2 sensors out at 60-90k miles. They are consumable items.

Yes, they can last longer, but the EPA mandated warranty is 80k miles (or 2,400/hours, whichever comes first).

At 128k, you got more than your money's worth out of them.

Also, don't run it too long with bad o2 sensors, you could look at replacing your cats, which is serious money.

 

You need to do a better job at fault description.
Which sensors are involved, there are four.
What does hrt mean? Is it the Ox sensor Heater circuits? if they are open, the sensors will not heat up until well into the drive cycles because they have to run at about 600 degrees. This indicates either an open or shorted wire harness under the truck. This also affects fuel mileage and the life of the converters.
Being in CA., replacement of Cats comes under pretty strict state regulations and gets pretty expensive.
You begin to see the importance of better info, other wise it cost you more hassle and money tryin g to guess you way out of the issues.
What you indicate can have 6 or more different codes to ID which and how many items are involved and lead to what the repairs are..
You can't guess and short cut around this.
Good luck.

 

sorry about the description . i used an obdll scan tool and the 2 sensors that continue to show not ready status are o2 and hrt . the scan tool registers no trouble codes or pending codes .
just can't get the last two sensors on the scan tool to clear . guess i need to take it to a shop and have it properly diagnosed . thanks for all the input .

 

Bluegrass - HRT is O2 sensor heater monitor.

 

Yes, I said that must be it in my reply just to be sure.
People who give descriptions with out code have no idea what is going on are very often wrong.
The Ox Sensors are not directly called Smog sensors but if they set a code, that would indicate a failure to meet the limits, indirectly.
The Ox Sensors. run full time to keep fuel correction under tight control AND detect out of limits operation on a secondary basis..
It appears the Heaters are not working. That will result in failure to pass diagnostics as stated.
Using fuel additives on cold Sensors will do nothing. That's why it did not help.

 

finally got my 98 ford f150 smoged after 4 weeks . i replaced the o2 sensors as was suggested . cleaned the throttle body and maf sensor . did at least 6 obd2 drive cycles and the monitors still would not reset . finally went to the local ford dealership and was informed that they no longer work on smog issues in california due to the states onerous regulations . i was referred to a smog shop that they send all their clientele . turns out that when i had the exhaust manifold gasket replaced the mechanic replaced the thermostat with one set at 160 degrees . all full size trucks require a thermostat to allow the engine to get to a minimum temperature of 200 degrees. once the thermostat was replaced with one set at 195 degrees , the monitors all reset on one 10 minute drive cycle . if the engine runs to cool the upstream sensors will read correct , but the downstream behind the cat will read too rich or to lean and will not allow the monitors to reset . the o2 heater must reset before the o2 sensors will reset . it requires an operating temperature above 200 degrees . so not being a mechanic i hope i explained this in a way that will help others that have had o2 sensor monitor reset issues . thanks to all of you on this forum for your guidance and assistance , much appreciated . california is smog hell .......

 

With all due respect and not knowing about what you might have been told, your reply is not correct.
A low temperature under about 175 is detected by the computer as not heating up in a certain amount of time from a cold start. It has a code assigned.
Next, the CHT has nothing to do with Ox Sensors down stream in the exhaust for their testing sequence because they have their dedicated Heaters for fast heat from cold starts that begins at the instant the Ignition switch is turned on to supply them 12 volts.
Next, the rear Ox Sensors also have Heaters but only monitor the Oxygen stored in the Cats. They are way down stream and used to access the performance of the Cats and have no other >>controlling<< input to the computer, The functions monitored have their own codes such as 420/421 etc. Look them up.
A failure of the front Ox Sensor heaters can keep the test from completing because the Sensor has to get up to 600 degrees from the exhaust in order to work and permit closed Loop fuel control.
Refer back to reply #5.
Good you got things cleared up and pass inspection.
Good luck..