Last night my check engine light came on, so I took it to Auto Zone to have the code checked. Well it came up PT 1131. The guy told me that is was the o2 sensor-lean. So I was wondering if anyone could explain this to me. How do I figure out which sensor it is. The guy at auto zone told me that there were pre-cat sensors and after-cat sensors.

Along with the light I had a fairly rough idle and it seemed to feel like the truck wanted to die. I guessing that since it is lean that it just wasnt getting enough gas? This has been a problem that I have been having off and on for about a year or so but the light would go off before I was able to have it checked.

So if anyone could help me out with this I would greatly appreciate it.

Thanks Ryan

 

I had the exact same problem a few months ago, but I was throwing a couple more codes along with the P1131. I went ahead and replaced both o2 sensors, even though the codes were pointing to the passenger side sensor. I don't think there are o2 sensors after the cats. After I replaced them, everything was back to normal.

 

P1131 - Lack of HO2S -11 Switch, Sensor Indicates Lean. A HEGO sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time. Possible Causes:

1- Electrical: Short to VPWR in harness or HO2S. Water in harness connector. Open/Shorted HO2S circuit
Corrosion or poor mating terminals and wiring. Damaged HO2S. Damaged PCM
2- Fuel System: Excessive fuel pressure. Leaking/contaminated fuel injectors. Leaking fuel pressure regulator. Low fuel pressure or running out of fuel.
3- Vapor recovery system .
4- Induction System: Air leaks after the MAF. Vacuum Leaks.
5- PCV system. Improperly seated engine oil dipstick.
6- EGR System: Leaking gasket. Stuck EGR valve. Leaking diaphragm or EVR .
7- Base Engine: Oil overfill. Cam timing. Cylinder compression. Exhaust leaks before or near the HO2S(s)

Regards

Jean Marc

PS. -11 switch is the passenger side up stream of the converter sensor.

 

Hey thanks guys. This will help out alot.

How hard are the sensors to replace and where exactly are they located? If possible I would like to do it my self instead of paying a shop to change them.

Again thanks Ryan

 

They took me about an hour to do both. They are sticking out of the exhaust manifolds. you can see them from above, but they are easier to get to from the wheel wells.

 

Before you waste your money on O2 sensors, look for vacuum leaks and ck the plumbing to your air cleaner, most of the time this code is not set due to bad 02 sensors