hi i just bought a 98 tacoma yesterday, i just failed smog, by two things

1 the check engine light is not working , when you turn the key to on all the lights in cluster should on right? once you fire it up all the lights should be off, now the check engine light is not on at all, could it be just the bulb or other stuff?

2 its throwing a code

P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1)


i see there are two sensors before and after the cat

does this mean i need a new cat or the sensor(s) is bad?


tail pipe emission passed but somehow close the max numbers , but it still pass


pls give me a hand , any help will be really appreciated

thanks peace!!

 

I think it's suspicious that a newly sold truck would have an inoperative MIL AND a P0420. One wonders if the seller disabled the MIL to make selling a truck with a bum cat easier (probably a Federal offense). But I'm a suspicious guy. Of course, it could be the bulb.

As far as the P0420, it could be an exhaust leak, a sensor, or the cat. You are at a disadvantage if you don't know the age of the sensors. If the front sensor is less than 70K and the rear sensor is older, replacing the rear sensor for a solo p0420 is a very good bet. In your case, however, you could do both sensors and still end up having to do the cat. A good tech with an OBDII scanner that will graph the o2 sensor outputs can make a pretty good guess what is going on. The dead MIL leaves me suspicious that it is the cat. I hope I'm wrong.

I'm pretty sure the FSM has a trouble shooting procedure for a dead MIL. If you could get that resolved, and it doesn't look deliberate, I'd probably take a chance and do the rear sensor. Front sensors usually throw other codes together with or instead of P0420. That said, they do tend to fail before the rear ones do. The ONLY purpose of the rear sensor is to set P0420.

You could look at the nuts on the sensors themselves to get a clue to their age. They tend to rust up pretty good by the time the sensor is old enough to fail.

 

I agree, I think something fishy is going on here. According to the Cali DMV website:

"When a car is sold, who is responsible for the inspection?

The seller is required to provide the buyer with a valid smog inspection certification at the time of the sale or transfer. Smog certifications are good for 90 days from the date of issuance.
The inspection is not required on a transfer if a biennial smog certification was submitted to DMV within 90 days prior to the vehicle transfer date (a vehicle inspection report may be required for proof of certification).
NOTE: Smog certifications are not required for transfers that occur for a gasoline powered motor vehicle that is four or less model years old. (Determine the oldest-qualifying year model by subtracting three from the current year) the four or less model years old rule does not apply to diesel powered vehicles. A smog transfer fee will be collected from the new owner."

 

I definitely suspect bulb is either missing or burnt out. It's not hard to take the IPC out and check. If you have someone with a good scan tool I would check the O2 sensor parameters and see if B1S1 and B2S1 (depending on system) are both fluctuating from 800mV to 200mV (can fluctuate more or less again depending on system). If they are fluctuating properly then I'd look at the S2 data. It should be reading fairly steady usually from 550-650mV (again depending on system). If they all look fine then 95% of the time the cat has failed. Unfortunately for you if it is the cat then you are already past the Federal Emissions warranty. Meaning up to 8 year or 80 k then you can have the cat's replaced for free under warranty.

 

thanks for the input guys,


i had the same thought that the seller took the bulb off so there is no check engine light

but i dont know man, its hard to tell, i think he is honest

i will take off the cluster tomorrow see whats going on

for the check engine light , if nothing wrong with the bulb , what should i do?


as for the smog thing , i knew it already, but still lots of people got the car without the smog for cheaper


where is the best place to get the back sensor? i looked around omg they are 80-100 bucks each, magnaflow carb legal cat is about 150 + 50 weld it on