Mechanics

02 SENSOR

2003 Ford Focus • 65,000 miles

I have a 2003 Ford Focus zx3 2.3 Litre motor.I have been having a misfire code PO302 cylinder 2. It is a unusual problem because it cuts out when ac is turned on turn it off it is fine, but some times it will cut out without ac running. But I have a another DTC number, well we had Pep Boys scan it and it came up with P2274, and I think it suppose to be P127, 02 Sensor Signal Stuck Lean-Bank 1 Sensor 3.I understand the bank one front of motor, but where is Sensor 3 located. And does anybody out there know how to test them. Thanks
Avatar
Randy sharp
June 17, 2013.




One thing to consider with the type of symptoms you described is a bad diode in the generator. That will reduce its maximum current output to exactly one third of its rated value which is not enough to run the entire electrical system under all conditions. A professional load-test will show that. With one bad diode of the six, "ripple" voltage will also be very high.

As for testing an oxygen sensor, the Engine Computer does that for you. You can watch its signal on a scanner, and you can introduce rich and lean conditions to see if it responds, but you have to remember they only measure unburned oxygen, not unburned fuel.

Normally when three oxygen sensors are used, number three is the one after the catalytic converter.
AD

Caradiodoc
Jun 17, 2013.
So your saying the alternator could have a bad diode, but I just replaced the alternator about a year ago. And the 3rd 02 sensor is after the cat. Let me ask you a question my friend, you seem very knowledgeable, on mechanics.I want to purchase a 0BD 2 scanner, what kind would you recommend?And I surely appreciate all the help and advise you have given me.

Tiny
Randy sharp
Jun 17, 2013.
A bad diode is just one of the possible causes of what you described but it's an easy one to quickly rule out or find with a professional load-test. That involves drawing the maximum possible current for a couple of seconds to see what can be delivered, not a simple voltage test. Measuring battery voltage while the engine is running will tell if the generator is working but not if it is capable of delivering the full current it was designed to.

As for scanners, I have the Chrysler DRB3 because with an extra plug-in card it will do emissions testing on all brands of cars sold in the U.S. On '96 and new models up to at least 2004, and a few models beyond that. With another card it will work on all Chrysler products back to '83 models.

I also have the Chrysler DRB2 made for all Chryslers from '83 through '95 but it requires various plug-in cartridges specific to the line of models you're working on.

If money is no object, Snapon has the MODIS and a few other models but they get you with expensive updates every year. My coworkers used a Genysis and liked it a lot but I never used them so I don't know much about them other than they're a popular, less-expensive alternative to the Snapon stuff.

You also have to look at the cars you're going to be using this on. '95 and older models had all different computer systems. For those, other than Chrysler products, I have a Monitor 4000. One cartridge lets me work on GM, Ford, and Chrysler, but aftermarket scanners never do all the functions of the manufacturer's scanners. Starting with '96 models the manufacturers started trying to standardize their computer systems, at least as far as the computer language they used. All of those models have the "OBD2" emissions system, (on-board diagnostics version 2). Besides being able to get really specific with well over 1000 potential fault codes, that is when they added the oxygen sensors after the catalytic converters to monitor how well they're working. To my knowledge everything through the 2003 models uses the OBD2 system. You need a scanner that conforms to that language if you want to use it on this car.

Starting with a few 2004 models they switched to the current "CAN BUSS" system. That stands for "controller area network". Every switch and sensor becomes a small computer module, right down to the headlight switch and door switches. The chances of developing electrical problems skyrockets but supposedly the many on-board computers do much of the diagnosis for you. I've only worked on a few trucks so far and it has always been an expensive computer that has solved the problems. I DO know I will never own another new car after seeing how ridiculously complicated they're designing them now.

New scanners are real expensive but they become obsolete real fast too. You might look on some online auction sites for used ones. Larger repair shops have multiple scanners so no mechanic has to wait to use one, but when they start to see fewer older cars they will often sell most of that equipment and just keep one on hand in case one of those cars comes in. Don't waste your money on a simple code reader. Many auto parts stores will read codes for you for free. Full scanners display all the data the various computers are seeing from the sensors in real time. They also access all or most of the computers on the vehicles, not just the Engine Computer. They're "bidirectional" which means along with receiving and displaying data, you can talk to the computers and command them to do things like fire injectors and ignition coils, and turn the radiator fan on and off. Those things are real useful when diagnosing problems.

One thing you'll get with the Snapon MODIS, and possibly others, is troubleshooting tips that aren't included in manufacturer's scanners. It has a section that gives you the description of fault codes and things to check. The list of stuff to check is pretty basic for an experienced mechanic but it can be real helpful for guys like me when we aren't familiar with the car we're working on. Some tests get right down to telling you which wire color to test and what to expect to find. I always taught my students to figure out those test points on their own so they could do it when they didn't have a book or scanner to tell them what to do, but for people with no electrical training those test steps can often lead you to the cause of a problem and save you a trip to the mechanic. If you plan on keeping your car a while, $3000.00 for a used scanner can save you more than that in diagnostic costs at the repair shop.

Caradiodoc
Jun 17, 2013.
Like I said before thank you so much for the information you have given me, I have been working on cars since I was 15 years old you know with dad, but I am not ase certified. Are you a teacher or something you are very knowledgeable about vehicles. Thank You for your time.

Tiny
Randy sharp
Jun 17, 2013.
Was a tv / vcr repairman for over 40 years, mostly part-time. Was a mechanic during the same time, seven years at a Sears Auto Center, then ten years at a very nice family-owned Chrysler dealer. Then taught in a community college for nine years. My specialty areas are Electrical, Suspension and Alignment, Brakes, and Engine Repair.

Caradiodoc
Jun 17, 2013.

AD