Pending Code P1131, No CEL

[diego_0]

Hello, I just got this 2000 Ford Ranger 4.0. It was missing a bunch of parts, I got everything back together but now I got a pending code P1131. I am trying to get all monitors ready but once this code comes out pending (no CEL) the last monitor (catalyst) won't reflect readiness. The only symptoms I get is that the car will randomly shut down while driving but it will start right back up and sometimes even if I floor it the RPM stays low around 2k, and highest speed 55mph. So far I swap O2 sensors, replaced PCV, fuel filter, crankshaft sensor and check fuel pressure (around 64psi). Thank youuu

 

[diego_0]

I know you already replaced the fuel pump so now you should check the wiring for the O2 sensor, the one before the Cat on the passenger side. Let me know If you find anything

 

[RonD]

P1131 Lack of Upstream Heated Oxygen Sensor Switch – Sensor Indicates Lean – Bank No. 1

Always good to post the code definition so we are all on the same page

Bank 1 on a V Ford engine is passenger side, drivers side is Bank 2

Upstream means O2 closest to engine

Because there is not a P1151 Lack of Upstream Heated Oxygen Sensor Switch – Sensor Indicates Lean – Bank No. 2, Code

Then you know its not an issue that would be common to BOTH banks of the engine, like, fuel pressure, MAF sensor, upper intake vacuum leak, pretty much anything that would effect both sides of a V engine

Which leaves exhaust leak on Bank 1 exhaust manifold, this sucks in air as well as leaking exhaust so O2 sees Lean
Vacuum leak in lower intake manifold on bank 1
Bad O2 sensor or wires on that Bank

Dirty injector on bank 1 so leans out fuel mix in a cylinder

You didn't mention misfires, but a misfire on bank 1 can cause that code as well since no air was used up in ignition so air is dumped into exhaust and O2 sees Lean

If you have a OBD2 reader you can usually watch Live Data
O2s are numbered this way
B1(bank 1)
B2(bank 2)
S1(upstream)
S2(downstream)

So B1S1 would be the upstream bank 1 sensor setting that code
B2S1 would be upstream O2 on the other bank to use to compare data

With engine running see what both show on the screen, if voltage is available use it
0.1v is Lean
0.9v is Rich
At idle mixture is rich, so raise RPMs to say 1,500 and hold it there, but driving is better
Should change fast but stay between 0.3 and 0.6, 0.45 is the sweet spot computer tries to get

If you just have Fuel Trims, a %, then -5% to +5% is what you want to see
Higher than +20% is what sets Lean codes on a bank, +15% while accelerating is normal but should settle down to under +10% while cruising
Fuel trims are OPEN TIME for injectors, so not O2 sensor data, % is difference between computers calculation and O2 feed back
So if computer calculated 100millisecond open time for injector to add the right amount of gasoline
And O2 showed Lean then computer would open injector longer to add more fuel, so +2% would be new open time of 102ms
+10% 110ms open time
So if its off by 20% there is something wrong in the system

O2s can not work until heated above 650degF so only start working after 5mins or so after cold start, which is why they are "heated" O2 sensors, to get them hot ASAP

 

[diego_0]

Thanks RonD, I double checked my headers on Bank 1 and they are tight as well as the 2 bolts from the Headers to CAT. I unplugged each injector on Bank 1, one by one and I could hear the RPM going down everytime. P1131 is the only code I get, no misfires and the code is pending comes and goes. It prevents the all the monitors to get ready for smog.

 

[RonD]

Look at the data from the O2 sensors after warm up
B1S1 and B2S1

If they don't "look the same" then either replace B1S1 or swap them around and see if you then get P1151, so code followed the O2 sensor, replace sensor
If it stays as P1131 then either its a wiring issue at that O2 or PCM issue
As said above, 0.1 volt is Lean, so 0.0v is also lean(no voltage from O2), so bad wire can be P1131

O2s have 4 wires
12v key on for heater
Ground from computer for heater

Reference ground from computer
0.1v to 0.9v out to computer

O2s generate their own voltage, using a chemical reaction after they are above 650degF
And its under 1 volt
So any wiring issue on one of the 2 "sensor" wires goes to 0.0v, lean code

 

[diego_0]

It fluctuates, but what I did before I swap the B1S1 for B1S2 before and it gave me the same code.

 

[diego_0]

After driving for a while just parked and the other sensor it's showing a reading.

 

[diego_0]

RonD you are genius, yes it was the O2 sensor, I guess when I swapped i, I bent it.I replaced it for a new one and no more pending code. Thank you!!!!

 

[RonD]

Good work