Hey all,

I have searched already, but could use some help. I got P1131 CEL, truck running fine, no issues really that I can find. I clear code yesterday and as soon as I start truck it is back. I cleared it again, didn't start it and scanned again and it's back. I unplugged the battery, check codes with just ign. on and it is back.

I have checked all over for any kind of vacuum leaks, cleaned out the AFM and changed out the passenger side (bank 1) oxygen sensor. And the target....remains. Still coding.

I drove it, got it nice and warm, cannot clear this code. Anyone have any ideas? The wiring at the connection to the O2 sensor was pristine. I am not sure how to troubleshoot the heater circuit or what-not on this sensor to make sure it's not failing to even energize the sensor or if there is some other sensor in this circuit that could cause it to code like this. The engine knows it's bad before you even start it, so it would "seem" it must be electrical or another sensor in the line is failed out. Or the ECU is not sending the signal or juice.

Thanks for any help. I will take my own advise and see if I can find a wiring diagram :O)

 

Always good to post definition you are using with the code
P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1

No one has them all memorized, lol, and maybe its the wrong definition

Bank 1 is passenger side of V6 engine

Heater on each O2 will set a separate code if its not working
Heaters all get 12v from same fuse with key on, and each heater has a ground wire back to computer
Computer "sees" the 12v passing thru each heater with key on, it then grounds each wire to activate the heater, then ungrounds it every few seconds to test if 12v is still there

O2 sensors need to be above 650degF to detect oxygen, they are heated so they can get above 650degF faster than if just warmed up by exhaust heat, this lowers emissions
So after warm up O2 technically doesn't need the heater any longer
So wouldn't be a heater issue

For the sensor part, the O2 generates its own voltage, 0.1v to 0.9v
0.1v is lean
0.9v is rich
In the truck side of the O2 sensor plug there will be an Orange wire, that's the computers reference ground, pin 91 on computer, its the grey/red wire found at other sensors
You can use an OHM meter to test Orange wire to another sensor's grey/red wire, should see 0 ohms or low ohms, or use a continuity tester
Grey/red and orange wires are spliced together in the harness, all 3 O2s use/share the same orange wire

On O2 sensor 1 plugin, on a 1999, there should be a grey/light blue stripe wire, that runs to pin 60 on computer thats the wire that has the 0.1-0.9volt
You can test this with engine running

I would just use your code reader to watch Live Data coming from O2 S1B1 to see what computer is seeing as far as voltage from this sensor
If you can't do live data then get a $20 OBD2 bluetooth reader, they can

P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1
This means voltage is staying at 0.0 or 0.1 on this O2 sensor, so if you have changed the sensor then its a wiring issue on orange or grey/blue wire, OR computer circuit failure

 

thanks Ron! I will post back what I find out. I don't have a code reader that does anything but tell you the code and erase for an older OBDII connector. I have a pretty decent one for newer cars, but don't know how to hook up to the Ranger since the connector doesn't fit. I will do some testing with ohmmeter on that circuit.

 

Spend the under $20 for an OBD2 bluetooth reader, APPs are free
You can watch live data on those

ODB2 was standard plug from 1996 and up on ALL vehicles sold in North America, its is the LAW, not optional for car makers
So you newer one must work on a 1999 Ranger

 

My wife drove it to work yesterday and now the code is gone (which she didn't mention) My "good" obdII does hook up to the Ranger. I thought that the connector was an old style one. So, I guess the new sensor needed a couple cycles to start working or something. All good now. I can see the live data is putting anywhere from .35 - .75 when I was watching on both sensors.

Cool thanks for your help!

 

Good stuff

Thank for updating your thread, it WILL help someone else