Hey everyone,

I don’t need help (for once) but wanted to share my weekend experience in case someone else can learn from it.

On Saturday night, the ‘Check Engine’ light came on in my wife’s ’02 Monte. Sunday I drove to an auto parts store and had the code read; it was P0171 – ‘Bank 1 too lean’. Run back home – do a little online research here at MCF and elsewhere. Quickly found out that it could simply be a dirty Mass Air Flow (MAF) sensor.

OK, so clean the MAF sensor, right? Disconnect the battery, disconnect the MAF sensor connector, then get ready to remove the two screws mounting the MAF sensor. Then quickly discover that the two screws holding the MAF sensor in place use security torx heads – the kind with the little post in the middle. So my torx bits won't work. So reconnect the battery and make another trip to the store to buy some security torx bits. (As far as I can tell, those are the only two screws on the entire car that use security torx heads. What’s up with that??)

Once the MAF sensor was removed, it was a simple process to clean the sensor. I used electrical contact cleaner (not brake or carb cleaner – those can leave a film) to spray the two thin wires that form the heart of the MAF sensor. You can buy ‘MAF Cleaner’ but as far as I can tell it appears to be electrical contacts cleaner by a different name. (Someone correct me if I’m wrong there.) Electrical contact cleaner is alcohol based and dries very quickly without leaving any residue.

After re-installing the MAF sensor and reconnecting the battery, the code had cleared itself. Ran some errands with the Monte and the code did not reappear.

And there was much rejoicing.

Very easy job - once I had the right tool. And much cheaper than having my wife take her car to the shop for diagnosis / repair. They probably would have installed a new MAF sensor at significant cost.

Lessons learned:
- Take advantage of free service ('Check Engine' code reading) provided by local auto parts stores
- Use MCF and other online resources to determine possible causes / resolution based upon the code shown
- Pay back the generosity of the auto parts store by buying necessary tools / parts from them
- Do the work yourself, save a bundle, and learn more about your car

In nearly 150K miles, my wife's Monte had never 'thrown a code' before. So the process of figuring out what's wrong based upon the code was new to me. Luckily this first one was pretty simple.

 

The TPS and IAC sensor on the TB also use the T-20 Security screws

Usually in these threads I mention to people that they need this type of Torx for the job.

If your code comes back, remember to check your o2 sensor on your rear exhaust manifold, if it has never been changed before with those miles, you may need to do it. I just recently did it on my car.

 

Thanks, Mike. I now have a complete set of security torx bits through size 30, so I'm ready for the TPS and IAC sensors!

I had expected the O2 sensors to be mentioned more. Surprised I didn't see much. Both O2 sensors are original - so they are both in need of replacement. They are on my 'To Do' list.

 

Great info to pass on Sparky!! I'm certain your findings will help someone.

When I was modding the L67 TB (now on my Monte), two of the original security torx busted, I removed all the security torx screws and switched to stainless steel hex heads. Hopefully I am now clear of that ever happening again.

To tack in about the O2, I can't confirm, but I heard the most reliable ones to use in GMs are Delphi and AC Delco. Some people have had issues with Bosch (so far I haven't, but I not put on on the Monte).

 

Thanks, Maniac. One reason I haven't replaced my O2 sensors yet is that I wanted to research what brand to use. Bosch are one of the first to pop up in any search. I wanted to check out NGK as well. I like their spark plugs; don't know anything about their O2 sensors though.

 

I stuck with the original ACDelco model AFS109 (off Amazon, I got it for $43 shipped), they are a little more expensive, but like Jason said, these cars can have issues with inferior sensors.

I wouldn't worry about the rear o2 sensor, just because it's sole purpose is to read the cat, but you will know if the cat is bad just by smelling the car, or watching it struggle on hills.

A little help on changing the o2 sensor.

I know some people do NOT have the California Emissions Pumps on their 3800, but I still find removing the dog-bones and rocking the engine forward a necessity when doing any work to the rear of the motor. Use a specific O2 sensor socket (a good quality one is needed) And just unplug the sensor before you tackle it. (I also disconnect the negative terminal whenever I do anything with sensors). When you put the new one on, I believe the torque is 35/36 ft/lbs.

*Edit, I think I'm also going to make this a sticky in the How-To Section*

 

I should have mentioned, after modding my Monte, I destroyed the factory O2 (not knowing my PLOG had a internal coating that was going to burn off). I first popped on a Denso (well after the coating burn off should be gone). Week later it had one issue related to PCM tuning and the other was the code that prompted me to replace the O2 (low volts code, don't recall the number).

I am currently riding on a Delphi (about 1000 miles now on it). NO problems. But after reading Chibi's O2 replacement info, I wish I would have gone with the AC Delco one "just because" it's true OEM.

 

Thanks, Mike! I wasn't aware an 'O2 sensor socket' existed. I've learned the hard way that having the right tool makes all the difference in getting the job done.

 

It has a slit down the side and is a deep socket. The slit helps you feed the wire through and you can use a socket instead of a wrench.

Here is the actual one I purchased:

Amazon.com: Lisle 12100 Oxygen Sensor Socket: Automotive

There is also something called a thread chaser, they are good to have for changing spark plugs AND o2 sensors because after you remove your old plug, sometimes there can be stuff left on the threads that make the new plug screw it poorly or not straight. This is something that you screw in and then remove and it will clean the threads. I got one that was double sided (one for o2, one for spark plug) and you just have to use a 15mm deep socket on it. But you can also find brushes and such to clean them out if you want.

 

I just put the Lisle socket on my Amazon Wish List moments before seeing your message. Great minds think alike.

I haven't seen the 'chaser' you mentioned. I'll have to check that out as well.