More P1151 Engine Check Code

[PaulZ]

Howdy, been away sick for awhile but back to driving my '99 Ranger 4x4 4.0. Getting the dreaded P1151 oxygen switching sensor. Read most of the threads here; ignition, fuel, vacuum leak, sensor itself,,, mine is unusual, maybe, as it only happens after full warm up, 15-20 minutes or so. And I get a miss fire around 2-3,000 rpm under light load, floor it and it goes away.

So far I have only cleaned the MAP sensor and looked at a couple plugs, I am hesitant to buy parts that may not be the problem. Do my symptoms match any others that have been reported?

Thanks,
Paul

 

[RonD]

P1151 Lack of Upstream Heated Oxygen Sensor Switch – Sensor Indicates Lean – Bank No. 2

So driver's side upstream O2 has lower voltage even after computer has opened injectors at least 20% longer than it calculated

O2 sensors are the only sensors that wear out, 12 years or 100k miles and then need to be changed
And they go LEAN when they are completely worn out, and at that point it has probably cost you $100+ in wasted fuel over the years past the 12 year mark

So how old is that O2 sensor?
If you don't know then change ALL the O2 sensors

Exhaust manifold leak will cause that bank to go lean
Lower intake vacuum leak on that one bank will cause lean
Clogged injector on that bank will cause lean


Upper intake vacuum leak or MAF sensor issue or low fuel pressure will cause BOTH banks to show lean

 

[PaulZ]

Thanks Ron!

Truck has190k, I got it with 150 and no receipts. I’ll try a new sensor, good points on the MAF sensor and vacuum leaks.

What causes the sensor to “switch”? Cant find the connector, between engine and firewall just above trans I guess. Cant easily reach it..

Paul

 

[RonD]

O2 sensors generate there own voltage using chemical reaction with Oxygen in the exhaust
0.1v is high oxygen, lean
0.9v is low oxygen, rich

O2s need to be heated above 600degF to start to generate voltage, they have a built in heater to get up to temp faster, 2 of the 4 wires are the heater, 12v(key on) and a ground wire(each heater is monitored by the computer, there is a different code when a heater or power fails)

With engine running and O2s warmed up, the upstream O2s will "switch" very fast between 0.2v and 0.6v as the computer adjusts injector open time to get a 0.45v average, best power and MPG
This is millisecond switching, very very fast

When an O2 starts to run out of chemicals the voltage goes down, so FALSE LEAN, and computer runs the engine Richer than needed, not a lot but its costing you money
Over years the voltage is just not "switching" fast and then not at all, "lack of switching"

BUT........if there are other issues like steady misfires, exhaust manifold leaks, low compression, then O2 can also "Lack switching" because computer can't fix the issue by adjusting injector open time

First step is to change the O2s if you don't know their age, then you will be able to "trust" the code as another issue not a bad sensor report

 

[PaulZ]

Whew, that’s a lot to understand for a guy raised carbs, points and condensers, lol.

Drove it 20 miles yesterday, CEL never came on and it ran perfectly. Seems to only happen after more time and miles from cold.

Two other electrical glitches it has; 4WH, which I use to get up my dirt driveway, occasionally won’t engage, 4WH and 4WL lights just flicker on dash. And radio occasionally loses power. Again both work again after cool off, but I haven’t noticed a correlation between them and the CEL, nor a common electrical connector. I will try to correlate next time. I’ll also find that upstream sensor connector, somewhere above the bell housing, while waiting for new sensor.

Thanks again Ron!

 

[RonD]

Yup, me too
I am old so...............learned on carbs, points, timing, brake shoes and king pins

4WD lights flash when 4x4 controller gets "the message" from the dash switch to change but the electric motor on the transfer case does not move when sent 12v and ground

So dash switch is OK, and Controller is OK, transfer case shift motor or its wires are not

 

[PaulZ]

No more king pins either? What’s this world coming too?

I have an old backup 4x4, it has a big manual transfer case lever sticking up through the floor, no fancy electrical doo dads. But the carb really sucks the gas so I use the Ranger.

Just finally got that o2 sensor connector to where I could get a hand on it, but may have to pull the exhaust (or trans!) to get it apart. It’s above the bell housing with no room up top to get at it.

 

[RonD]

7/8" or 22mm crows foot offset wrench like this: https://www.amazon.com/OEMTOOLS-25249-Oxygen-Sensor-Crowfoot/dp/B004FEN9JG/?tag=959media-20

You can put the socket on the O2 and wrench it from under the exhaust pipe if there is no room above the O2, but some times the offset is enough to get it from above
Put socket on Upside down so extension hole is up higher if wrenching from underneth
Breaking it loose is the harder part, usually once its loose it will unscrew by hand

 

[PaulZ]

I got the sensor itself out of the pipe. It’s the electrical connector, which is another foot up above the bell housing, that I can’t get my hands on, top or bottom.

 

[PaulZ]

Hi Ron,

Finally changed the sensor yesterday. Had a tall, thin (and younger) guy get to the connector. I’ve only put 25 miles on it but so far so good, no misses or cel. But since the problem was sporadic and only when fully warm, too soon to tell. I won’t be able to drive it again this week, just wanted to report in and thank you again for your help.

 

[PaulZ]

Reporting back that after changing the one drivers side sensor, no more check light and no missfire, even passed a smog test. All good.

Aftet a couple of fill ups I’m only getting around 14 mpg. Would changing the passenger side sensor(s) help? It is a 5 speed 4.0, 4x4 with larger (265x16) M&S tires. Mostly non freeway driving.

 

[RonD]

New O2 sensors will give best MPG for 12 years or 100k miles

4.0l OHV 4x4 in the winter will be about 15/16mpg around town, so you are not too far off
Make sure you are compensating odometer miles shown for the larger diameter tires/wheels

 

[PaulZ]

There are two sensors on the passenger side, right? change both?

My door sticker says 245/75x16 tires. I have 265/70x16, Not much odometer difference seems.

 

[RonD]

1999 V6 single exhaust, yes 3 O2s total