Dylan Amell

I have an 02 honda accord that failed emissions, i took it to a shop that guarantees a pass by doing enough work to qualify for a waiver. He really didnt do anything but charge me $170 for a piece of paper. But he also told me that he thinks if i replace my mass air flow sensor all of my problems will go away. The fail codes were P0172, P0420, and P1259. He said i should just buy MAF sensor and replace it in the car. But upon a little research by me, the 02 accord doesnt even have a MAF but it has a MAP instead... are these the same thing? Should i just replace the MAP?

hondamark35

you're correct, you don't have a MAF on your Accord. I would take this as a sign to disregard everything you were told at this shop and get a second opinion.

the first two, P0172 and P0420 are related to the O2 sensor output. P0172 can be triggered by a dirty, disconnected or failed MAF (in vehicles so equipped) but by way of the O2 sensor. P0420 typically indicates an ineffective (dirty or damaged) catalytic converter. to do this, the system monitors the output of upstream (primary) and downstream (secondary) O2 sensors. a large difference between the two tells the computer that the converter is cleaning things up. a small to no difference says the converter is no good.

the P1259 is related to the VTEC system. my understanding is that it's normally just a clogged screen for the VTEC solenoid.

What I would suggest you do is put a primary O2 sensor on (not terribly difficult on these vehicles), clean and/or replace the VTEC solenoid screen/gasket and clear the codes from the ECU (pull the Backup fuse for 10 seconds or use a code scanner if you have one). drive the car. if the codes don't come back, it's fixed.

MAD_MIKE

• P0172 Fuel system too rich
• P0420 Catalyst system efficency below thrshold NOTE: This does not mean the catalyst is dead, ignore this code for now.
• P1259 VTEC system malfunction.

Not the same and no you don't need to replace it.

You can do the basics yourself.
Give your car a tuneup, cap, rotor, wires, sparkplugs, adjust the valves, verify the base timing is correct, remove the upper plenum from the intake and clear out hte main EGR port.
Verify there is no oil in the spark plug tubes, if so you will need to replace the spark plug tube gaskets.


P0172, verify fuel pressure is correct first. If it is not you will need to correct this.
If fuel pressure is correct, you will need to start the engine hold it at 3K rpm until the radiator fan kicks on.
With a scanner watch the voltage output of the primary O2S.(engine should be in closed loop)
If it is stuck at .3V or less or .6V and more the O2S is most likely stuck/lazy and no longer functioning and needs to be replaced.
If the primary O2S is functioning correctly, use a vacuum pump to check the EVAP cannister purge valve.
If it holds vacuum verify valve clearance.
If it does not hold vacuum, replace the purge valve.

PO420, ignore this for now.
If the engine is out of tune or there are other codes present then the engine will not run at optimum.
If the engine is running poorly then the catalyst will not be able to properly function.
Too rich or too lean exhaust enters the catalyst then it will have a too rich or too lean output and fail emissions.
It is too expensive and critical of a component to simply blame it.
Most po-dunk shops will to get a few hundred out of you and the car may still not pass or barely pass emissions.
Fix the other codes first and verify catalyst functionality prior to replacement.

P1259, this could be the oil pressure is low(also check oil is full), oil pressure switch is faulty, or the wiring, or the VTEC solenoid itself, check your PM for a useful link.