I got the P1131 code and the check engine light is on. I cleaned the MAF and eventually installed a new one. The light stays off for about 1 week and then like clockwork, comes back on. What are the chances it is the HO2S? Any suggestions before I take it to my mechanic? Thanks.

 

Welcome to FTE.

You've not given us much to go on, as we don't know what your driving, how it's equipped, mileage, maintenance history, how the problem came about, ect, ect.

Since the list of things it could be is long, maybe read through this TSB & find your P1131 DTC & refer up to the DTC 1130 trouble list & sort through it one by one, to see if anything stands out & seems to fit your failure scenario & check those things.
01-9-7***DRIVEABILITY - HO2S (HEATED OXYGEN SENSOR), CATALYST, AND FUEL SYSTEM MONITORS - SERVICE TIPS - OBD II VEHICLES ONLY

Let us know how it goes.

 

Sorry, here. It's a 3.0L, XL supercab with 229,000 miles. I'd say I put about 200-300 miles a week on it. Mostly city driving. It was suggested to me to repalce the MAF, which I did to no avail. Last year it did this and replacing one of the upstream O2 sensors worked. It just seems odd that the MIL will stay off for about 6 days and then come back on. I'd really like to solve this without taking it in. Would testing the other sensors with a voltmeter be of any value? Thanks. The TSB has been very helpful.

 

Welcome to FTE. I would encourage you to include your truck's specs in your signature.

After you replaced the MAF and the O2 sensor, did you clear the codes (you can do that by disconnecting the NEG battery cable for 15 minutes or so)?

 

OK, that info is helpful, but we need more.

With that mileage, a number of things are well past due for replacement, so it would be helpful to know where you are on All past & present due scheduled maintenance items, repair & replacement parts & which brand you've used, like plugs, wires, filters, ect, which model year it is, auto, or manual tranny, what the set trouble code Number is, ect, ect.

With the mileage you have & the delayed CEL cycle, I agree a lazy O2 sensor fits that profile, so it would belong on your suspect list, but test to confirm Before any part replacement, as you already know from throwing an expensive MAF sensor at the problem with no joy.

Yes a good quality digital multimeter can be used to back probe/check many sensors, but it's a real pia & a slow process.
If your going to do that, be sure to check out the "Tech Info" thread atop this forums thread listing page, for all sorts of good info.
Scroll down to find a link to the 3.0L tech info page that Rockledge has posted, lots of good to know 3.0L things there.

A scantool that'll read various sensors live PID feed to the computer & it's output commands to various actuators is a much better way to go.

A scantools cost is way down, maybe 1/2 of what it was 5-6 years ago when Santa brought me my Actron CP9150.
One more diagnosis from it & I'll be money ahead, so it's been a worthwhile investment for me on all of my families vehicles!!!!

If you don't have, can't borrow, or don't want to invest in a scantool, run this puppy by your favorite autoparts store, as most will do a no cost computer trouble code scan, IF the CEL is lit.

Then post All of the code Number/s found, here, Before buying anything.

 

Yep, done that.

 

Plugs replaced about a year ago. I change the oil and filter religiously. Air filter replaced a couple months ago. Fuel filter replaced about 2 years ago. 95, manual tranny.

 

Ok, it's a manual tranny.

Your 3.0L has two upstream O2 sensors, so has the other one ever been replaced????
If not, it belongs high up on your suspect list.

Has the fuel pump ever been replaced???? If not, have you done a KOEO & KOER fuel pressure test lately????

WOOPS, I missed that your in Ca. & they won't let the autoparts stores do a no cost computer scan, so you'll need to pay to have it done, or invest in a code scanner, or scantool, or borrow one from a friend or club that has one.

Does the state permit the autoparts stores to have a scantool in their "Loan-A-Tool program & can you make loan of it, for a refundable deposit????

 

No. Just the one on the drivers side. Had the fuel pump replaced about 3-4 years ago. By scantool do you mean an OBD II reader? If so I can buy one at any auto part store. I think the O'Reilly's near my home advertises for free computer scans. When this first started I had it scanned on a code reader and it came back with the previously mentioned code.
Forgot to mention that I had the catalytic converter replaced last year. BTW, is the downstream sensor ever a problem?

 

No I don't mean a code reader. They read & maybe erase codes, but don't display live computer sensor data feeds (PID's), so they don't do much & thus don't cost much.

A scantool is more sophisticated, it'll do everyting a code reader will, but will also display live sensor data(PID's) to the computer, as well as the computers output to it's actuators, that it uses to control the engine.

SO, the scantool does a lot more & thus costs more, but they are about half what they were, say 5-6 years ago.

A good scantool will likely be $100-$200, depending on if it'll also do graphing, which is nice, but most of us don't really need that function, so the less expensive scantool that just displays numeric PID values, is all most of us need & they can now be had for about $100-150 .

I noticed Advance Auto recently had their Actrons on sale for half price, don't know if that sale is still on or not.
The price on upper end scantools is usually flexable, if you approach the store manager.

If the other upstream O2 sensor has never been changed, it's lived at least 2-3 lifetimes, as most folks replace them at about 75-100K miles, as their switching speed gets slow/sluggish/lazy with age, sorta like me!!!! lol

So as I posted above, it belongs high up on your suspect list, especially with 220+K miles on it.
The upstream O2 sensors are usually replaced in pairs.

Be sure to pull the B- battery cable before an O2 sensor installation, to wipe the computers memory, so it can begin to build new fuel trim tables with inputs from the new sensor & thus maybe avoid driveability problems. Also do the cold & warm idle strategy relearn routene, to avoid idle problems.

The down stream O2 sensor is just a cat converter monitor, to keep tabs on how it's doing it's emissions job & tattle on it, by turning the CEL on, if it lays down on the job, but this downstream O2 sensor doesn't affect how the engine runs.

 

Thanks. Right now I'm kinda leaning toward just replacing that sensor, but if I can find a reasonably priced scantool that sounds like a good investment. When I replaced that first O2 sensor I hadn't realized at that time that there were two until I took a closer look later at the schematic in the manuals (amazing how much more sense things make if you just pay attention). In the case of the O2 sensors is OEM critical or is aftermarket acceptable?

 

Well for sure OEM is good, if you use an aftermarket, use a quality part thats like the OEM design, so that the sampling & response time match up to what the computer program is written for.

I replaced both of my 94 Taurus 3.8L upstream O2 sensors about 2 years ago with Bosch, from Advance Auto & they seem to be doing fine.

Check out site sponsors for OEM parts, they'll likely have a better price than the Dealer, even with shipping.

Or if you have a Motorcraft Distributor locally, give them a try, mine even beat WallyWorld prices on some things & most parts stores on others!!!!

I opted for the Advance Bosch part as I needed them right away, they were in stock & I made use of their "Loan-A-Tool" program for the O2 sensor special socket kit, at no cost & I needed it's short off set split socket, for the Taurus rear bank sensor, that was in a tight limited space spot. Once in place, it made removal a breeze. Nothing like having the right tool for the job!!!!

I also used high temp nickel anti-sieze compound on the O2 sensor threads. Thank goodness when the factory put them in they did too, so the old ones came right out. Just be careful not to get any antisieze compound on the new O2 sensor tip.

 

Paw, I got a Bosch sensor and installed it today. The check engine light hadn't returned since I reset it last week but I went ahead and changed the sensor anyway as it wasn't very expensive. I won't feel really comfortable that it won't recur until its been off for a couple weeks but I'm pretty confident that this will work. I'll let you know. Thanks for all your help. TGC