My maxima 05, no modifications, 171K Miles, runs perfectly but the SES light came on, the code is p1273.

Went to dealer and did a diagnosis and the Service Advisor give the recommendations as below.
Valve cover and Intake gaskets, Bank 1 Converter, Manifold, Conv nuts bolts and gasket, A-Pipe, O2 Sensor B1, O2 Sensor B2, A/F Sensor B1
He also advised to change outer tie rods and do alignment. And the total labor and parts will cost $3970+TAX

I said no thanks, paid diagnosis fee $100 and came back to a local workshop near by. They checked the car and told outer tie rods are in perfect condition and alignment is good. He then fixed Valve cover and Intake gaskets leaks, replaced the O2 Sensor B1, deleted the code, Cleared ECU Self-learning (by disconnecting mass air flow sensor and battery trick - Link ) Parts and labor costed $350.
They also advised to use Lucas Fuel System Treatment 5.25oz. in tank and i did it.

After a week the code came back. Can any one advice what is the next step i can try

 

Dealer will just write work, that is what they do. They don't diagnose the problem. Neither did your local guy. He then preceded to do some backroom trick on your computer? Also Lucas fuel system stuff is snake oil.

P1273 could be a number of things. Exhaust leak etc. I would start by checking that.

 

local workshop guy checked the code (P1273) as per him possible causes maybe O2 Sensor B1, Fuel injector, Intake air leaks, Mass Air Flow Sensor etc

So he replced O2 sensor B1. As per him this sensor and (A/F) sensor 1 is same.
For Fuel injector he did a test drive and told injector is good just add the Lucas Fuel System Treatment in fuel tank. will it cause any harm?
He also told Intake air leaks will be ok when Valve cover and Intake gaskets are fixed.

How can we check to find out an Exhaust leak?

 

Start engine put on lift. Stuff rags in tail pipes and listen near engine and underneath.

 

I will check the Exhaust as you said.

i have seen a service bulletin form Nissan for maxima 05

It says

IF YOU CONFIRM
A rattle or buzz noise during acceleration
OR
A MIL ‘ON’ with DTC P1273 A/F Sensor
ACTION
• Inspect for a loose heat shield at the bottom of the Bank -1 catalyst. It may have
“separated”.
• If heat shield is loose replace the catalyst.

Mine the heat shields are missing. Do you think i need to replace the catayst?

 

I would have to look at it. Service bulletins will again just sell work and not diagnose what is happening.

 

checked the exhaust and didn't find any leaks

 

Did your mechanic use aftermarket or OEM O2 sensor. I am not a fan of aftermarket sensors. Only true way to find a vacuum leak is to use a smoke machine. If your mechanic does not have one, then find one who does. Lucas fuel treatment is more of an upper cyl lubricate than injector cleaner. Find a mechanic with a smoke machine and eliminate the guess work. If not. you may be changing parts for a long time before you find the issue. Good luck

 

As per the advises here we checked the exhaust thoroughly and found a tiny crack on one welded joint on the pipe coming to the catalytic converter(part of cat-bended pipe joined to cat).The heat sink was already found missing form the cat. So we replaced the cat and cleared the code.
every thing was ok but after around 1700 miles one evening the SEL came back on. I parked the car in my garage and next morning i noticed everything is back to normal. No SEL on, ride the car around 700 more miles and SEL stays off and car is running smooth and shows no symptoms of troubles.

I dont know what to do now.