stubborn SES light costing me a lot of $$$

You are better off getting codes read first for free at autozone. Lean codes don't usually point to the o2 being faulty, as it looks like you have found out. Check for vacuum leaks, possibly around the throttle body where rubber sleeve goes around it. Mine wants to curl up on the bottom side some times when I put it on, and unless I check for it, it is hard to see. If you can't find any leaks try putting the stock tube back on. If you have the kind that has an eblow in front of the MAF, they tend to throw off the MAF reading sometimes.

IMO..it's your rear 02 sensors.

You can "turn them off", but you'll need a custom chip to do so.

It's going to cost you money, but my adivise would be to go to a qualified tuner...(I prefer SCT)...they'll run the codes to be sure...burn a custom chip for you...disarm the rear 02s and make her run a bit better.

My rear 02's didn't act up with my Bassani catted X-pipe until the 2nd year I had the pipe on...and every Stang shop I visited were surprised it didn't happen sooner.

This is typical with an aftermarket mid-pipe.

Don't waste your money putting new rear 02s in...my bet is they'll be throwing the same codes in no time...get a chip and turn them off.

Get the code scanned and then let us know what it is.

ok........ you got MIL Eliminators?

this is what you need.
http://www.partshopper.com/shop/item.asp?itemid=262&catid=

/end thread.

http://eleanor.pro3i.com/showpost.php?p=5372403&postcount=6

start reading.

Rear o2's will not throw a lean code. Something else to check for is an exhaust leak.

Stangboy017 said:

i dont get it, like jstreet is saying, rear O2's don't throw the lean code I'm getting

Click to expand...

Cause jstreet knows the the rear o2's will only trigger certain codes, and none of them are these.
P0171 System Too Lean - Bank No. 1.
P0172 System Too Rich - Bank No. 1.
P0174 System Too Lean - Bank No. 2.
P0175 System Too Rich - Bank No. 2.


There rear o2's have one function only, and that is to give a voltage reading when the eec cycles through the series of obdii tests and gets to the one that checks for cat effenciency. It will throw codes indicating that it has failed the test, or it can throw codes if the rear o2 isn't functioning.

P0420 Catalyst System Efficiency below Limit - Bank No 1.
P0421 Catalyst System Efficiency below Limit - Bank No 1.
P0430 Catalyst System Efficiency below Limit - Bank No 2.
P0431 Catalyst System Efficiency below Limit - Bank No 2.
P0156 Downstream Heated Oxygen Sensor circuit fault - Bank No. 2.
P0158 Downstream Heated Oxygen Sensor circuit Voltage High - Bank No. 2.
P0160 Downstream Heated Oxygen Sensor circuit fault - Bank No. 2.
P0161 Downstream Heated Oxygen Sensor Heater circuit fault - Bank No. 2.
P0136 Downstream Heated Oxygen Sensor circuit fault - Bank No. 1.
P0138 Downstream Heated Oxygen Sensor circuit Voltage High - Bank No. 1.
P0140 Downstream Heated Oxygen Sensor circuit Faulty - Bank No. 1.
P0141 Downstream Heated Oxygen Sensor Heater circuit fault - Bank No. 1.



The lean code can be cause by a few things.
1. You really are running lean, which may be due to the MAF reading being off, or a vacuum leak.
2. An o2 sensor that is out of range and reading high. (not likely)
3. An exhaust leak that is allowing air to seep in and mix with the exhuast and throwing off the o2 reading.

The exhuast leak sounds the most likely if the car generally runs good otherwise, and you are getting the code only on one bank, and the fact that it happend right after the midpipe install. Even a pin hole size leak can throw off the o2's.