Occasional P1151 code - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 04-20-2014
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Occasional P1151 code

So I've had my truck about 5 months now. I think this is the 3rd time I've gotten a CEL & Code P1151 (according to my ScanGuage). I say think because I got a CEL a few weeks after driving it; but didn't save it anywhere. In the last 3-4 weeks I've gotten the code twice. At the same intersection on my way home from work.

No idle/driving issues, starts right up, drive 200', stop at a light for ~1min, then drive 45mph for 1mi, stop at another light, step on gas, CEL comes on. Again no rough idle, or hesitation, drives like normal. Finish the next 5mi home, clear the code & it went away until today.

Searching the boards/net seems like it can come from several things; but any insight on where to start? Leave it alone?

Truck has 154k mi, since I bought it I've only changed the oil, plugs, wires & ran some seafom in the tank (haven't 'smoked it yet!)

Probably unrelated, but I also changed the fuel filter, wheel bearings, upper & lower ball joints, shocks (4) and swapped 16" wheels for the 15's that were on it. Haven't changed the air filter yet; but the current one looks clean. Probably also unrelated but the oil gauge doesn't register for a mile or so, and occasionally the fuel gauge reads over actual amount (ie parked at night with 3/4 tank, ~100mi since fill up, next morning it read full)
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Old 04-22-2014
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I am not an expert, but looking at the code in google, the first link that comes up says that you most likely won't have driving issues. There are also a lot of easy things to look at.

With that said, I don't just leave things alone. I try to find the problem. I would start with the easy issues and knock them out first. Make sure the oil dipstick is seated properly. I know, sounds stupid, but do it. Mark it off. Check all your vacuum lines, have you overfilled the oil? Check all electrical connections. Is there any corrosion? Get some electronics spray, and hit the connections. I wouldn't be surprised if they were dirty with this amount of mileage.

This code comes up with low fuel pressure, so re-check your fuel filter. Are the lines connected properly? Check your gas cap? Does it seal properly?

Follow all your lines and connections from beginning to end.

A lot of this seems obvious, but you will be amazed at what you will find. A while back, I was getting codes, forget which, but it ended up being my gas cap. I didn't clear the code and I waited for it to go away on its own. It took a few weeks, but it worked!

I really like the $5 easy problems.
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Old 04-22-2014
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"P1151 - A Heated Exhaust Oxygen (HO2S) sensor indicating lean at the end of a test and is trying to correct for an over-rich condition."

Most likely just a loose or corroded connection at an O2 sensor.
You will have 3 O2 sensors, one on each exhaust pipe from the engine and one after the catalytic converter << this one is the one I would remove the connector on first, it gets the most water intrusion, check pins and slots for corrosion, clean if needed then replace and drive, see if code comes back.
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Old 04-23-2014
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Thanks, looked at the plug on the O2 at the cat; looked good at the connection. How hard is it to change? (ie can I do it with hand tools, or is it welded/torched in?)
The other 2 look real hard to get to; will try when I get some free time.

The gas cap is a replacement; I think its on OK. Dispstick & oil are fine; I haven't checked for a vac leak recently; I tried the first CEL months ago, couldn't find one by spraying carb cleaner all over the place.
Changed fuel filter in Dec, would it take 2-4 months to cause problems?

I did finally run sea foam thru the brake booster line; will see if that does anything. (ran some in the gas & oil a few months ago)

Thanks for the info
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Old 04-27-2014
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I went ahead and ordered 3 O2 sensors from rock auto, $20ea, I'm sure by the looks of other parts on the truck these are original or close to it.


I did set my scanguaage to read O2 bank 1 & 2, Short & long term fuel trim 1 &2.

There is no CEL now, Short term 1 & 2 were reading within +/-3 of each other, long term even closer.

O2 1 & 2 were wild! It was like watching an 80's sci-fi movie. 5, 69, 17, 23, 70, 2, and no where close to same numbers at the same time. Now I did watch a utube of an O2 diag, he had a fancy machine conected, giving an ociliscope wave form of the sensor, I suppose that's what the numbers could represent in a digital # format (and probably latent timing)

Hopefully the sensors aren't too hard to get to.

Also my tank mpg's have been averaging around 14 (+10% for the bigger tire size speedo compensation, still is only 15.4) I didn't expect much; but was hoping to hit the lower EPA number
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Old 04-27-2014
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Short term fuel trim(STFT) should look that way, very fast changes, that means O2 is seeing exhaust oxygen levels
.1 to .9 is the range .45 is the sweet spot for the front O2s

Rear O2(sensor 2) won't move as much



Long term fuel trim(LTFT) is easier to look at, lol, usually displayed as a %, +/- 5 is great, +/- 10 not so good but might not be a problem, above that means there is an issue.
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Old 04-30-2014
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Well got 'em done today... What a to get to!

The ones I pulled were Bosch with a Ford logo on them, probably original. Drove 15-20mi so far, no CEL (fingers crossed!)
Attached Thumbnails
Occasional P1151 code-img_20140430_140319%5B1%5D.jpg   Occasional P1151 code-img_20140430_142339%5B1%5D.jpg   Occasional P1151 code-img_20140430_152851%5B1%5D.jpg  
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Old 05-28-2014
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Well still no CEL; so I'm guessing this fixed it!
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Old 05-28-2014
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Good work

Thanks for the update on the fix
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