My wife's 04 Maxima is failing emissions. We took it to the dealer and they wanted $1100 for repairs. Negative. I'll try this myself. Here is what their paperwork reflected:

code #1273 - air flow system sensor failure

code #138 - oxygen sensor failure B-2

mass air flow alpha sensor readings AIN the lean percentile

their recommendations: air flow sensor replacement $480
O2 sensor replacement $375
fuel econ system service $170
idle control system relearn service $95

From what ive been reading code 1273 is any number of things. Some say O2 sensor, some say its the MAF. Does anyone here know for sure?

Also, code 138 says O2 sensor failure B-2. How do I know if this is BEFORE or AFTER the cat?

Im also confused as to where B1 and B2 is on this car. I know B1 typically is on the passenger side but as I look at the motor up top I see an O2 sensor behind the radiatior and another on the driver side of the motor. Which is B1 and which is B2?

I'm sorry this 1st post is so long but I gotta get this fixed ASAP. I feel like all the Atlanta area dealers are out to hose you. I spent 40 minutes on the phone with Conyers Nissan and no one could answer these questions for me.

MAF-$25 at junkyard
02 Sensor-$100
Fuel treatment(aka injector cleaner)-$10
IACV cleaning-FREE

None of this is hard to do

i know its not hard to do...and i know where to buy the stuff. what i need to know is
1 - is this code referring to the O2 BEFORE or AFTER the cat?
2 - i can see the upstream sensors, one is behind the radiator and the other is on the driver side of the motor...which bank is which?
3 - is 1273 a MAF code for sure?

Narco944 wrote:My wife's 04 Maxima is failing emissions. We took it to the dealer and they wanted $1100 for repairs. Negative. I'll try this myself. Here is what their paperwork reflected:

code #1273 - air flow system sensor failure

code #138 - oxygen sensor failure B-2

mass air flow alpha sensor readings AIN the lean percentile

their recommendations: air flow sensor replacement $480
O2 sensor replacement $375
fuel econ system service $170
idle control system relearn service $95

From what ive been reading code 1273 is any number of things. Some say O2 sensor, some say its the MAF. Does anyone here know for sure?

Also, code 138 says O2 sensor failure B-2. How do I know if this is BEFORE or AFTER the cat?

Im also confused as to where B1 and B2 is on this car. I know B1 typically is on the passenger side but as I look at the motor up top I see an O2 sensor behind the radiatior and another on the driver side of the motor. Which is B1 and which is B2?

I'm sorry this 1st post is so long but I gotta get this fixed ASAP. I feel like all the Atlanta area dealers are out to hose you. I spent 40 minutes on the phone with Conyers Nissan and no one could answer these questions for me.

The problems are pointing to Bank 1 only. Bank 1 (right bank) is for the cylinders 1-3-5 closer to the firewall while Bank 2 (left bank) is for cylinders 2-4-6 towards the radiator. Before replacing any component, check the air intake for leak and replace the air filter, if dirty. Also clean the main engine harness Ground Wire Connector near the Oil Filler Cap.

Make sure you got the code right as P0138 is for the Rear Heated O2 Sensor (downstream of catalyst), Bank 1, a.k.a. HO2S2-B1 (P0158 is for Bank 2). Refer to the link below, pages EC-198 for description and EC-203 for location.

P1273 is for the Air Fuel Ratio Sensor (traditionally known as the front O2 sensor, before/upstream of the catalyst). Refer to pages EC-481 for description, EC-486 for sensor location and EC-488 for connector location.

http://www.nicoclub.com/FSM/maxima/2004/EC.pdf

Please indicate if you have manual or automatic transmission. Below is the link to NICO sponsor, NGK.com, a.k.a. "sparkplugs.com," based on the assumption that your wife's car has an automatic transmission. AFAIK, the OEM O2 sensor is made by Bosch and is more expensive than the OE-equivalent NGK/NTK sensor. And if you are lucky, you may find better pricing at Amazon, provided you know the part number of the sensor.

http://www.ngk.com/results_app.asp

The Air Fuel (A/F) Ratio Sensor is relatively new and tends to get confused with the Mass Air Flow (MAF) sensor. There is only 1 MAF sensor (air intake) while there are 2 A/F sensors, one for each bank (catalyst). The A/F sensor has replaced the traditional Front O2 (before/upstream 'cat') sensor. A different type of sensing element is used for the A/F sensor and is typically more expensive than the traditional O2 sensor. Under ideal air-fuel ratio (Stoichiometric condition, 14.7:1) an O2 sensor output voltage to the ECM is @ 0.45 VDC while for the A/F sensor, it's 1.5 VDC.

yep, thats thge correct code for sure. i copied it down exactly as it was on the dealer printout. so, it seems that 1273 is the upstream a/f sensor, but why doesnt it specify which bank? and am i correct in assuming that 138 is downstream b/c its not labeled as an a/f sensor? is bank 2 the driver side on the downstream?

As in my previous post, both codes are for Bank 1 - P1273 for the A/F (front) sensor while P0138 is for the Rear O2 sensor.