Question about OBD-II scanners? | Ford Explorer Forums - Serious Explorations

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Question about OBD-II scanners?

Adam Berger

Well-Known Member
May 15, 2002
Reaction score
City, State
Melbourne, Australia
Year, Model & Trim Level
1999 XLT 4wd
I am currently looking into purchasing a code scanner (not a reader) and have been doing a bit of research on them. There are a heap of scanners available on Ebay but am not sure which one to buy and which one will work. I have so far learnt that Ford uses the PWM protocol for communicating. My question is, which scanners support this protocol, or do all OBD-II scanners support this anyway?
My problem with my Explorer is it is quite thirsty. It's drinking at the rate of 19litres/100km. Alot more than it used to. I am thinking that there may be a faulty sensor causing this but am not sure. I don't have a check engine light on, so does anyone know if you can have O2 sensor faults without the CEL coming on?
Does anyone know if O2 sensor codes are generic or manufacturer specific codes? There appear to be scanners that do only generic, some that do both and some that do ABS and airbag codes aswell.
I currently have my Ex booked in at Ford for some diagnostics but have to wait 2 weeks to get in. I don't even know what they charge to do this. If anyone has any input, suggestions or tips then they will be greatly appreciated. I have a little bit of time to make a decision on buying one or not.

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You did not mention how many miles are on your truck. Certainly some regular maintenance can help with poor mileage. Before I took my truck in for $60 per hour work I would be sure plugs, wires, air filter, fuel filter are all fresh. If more than 35,000 miles on o2 sensors, I would change them (upstream sensors). A dirty mam (mass air meter) can also cause poor mileage. A good electrical parts cleaner sprayed on those mass air meter wires will clean it up.

To properly calculate fuel economy try to buy fuel from the same station from the same fuel pump each time. Then only fill tank till pump automatically shuts off. Don't top off. This will help ensure equally filled tanks each time.

I have been using Autotap diagnostic software for several years now. It is most handy when software is loaded onto a laptop computer. I purchased the Ford full diagnostic package. Supposedly I can see averything that Ford techs can see. I particualarly like the data logging feature, where I can log the parameters of interest to me while on a chassis dyno. This feature is most helpful when really trying to get some tuning dead spot on. With data logging along with wide band O2 sensor data one can see exactly what the enginge is doing - such as whether engine is transitioning over from closed loop to open loop operation. On my '98 the engine was vitually never making the transition from closed to open loop operation and under heavy acceleration still running dangerously lean at nearly 14.6 : 1 and not making the power it was capable of making.

Get all the easy maintenance items done before turning loose the high priced Ford techs. Try to buy fuel with the least amount of ethynol in it as possible. Regular gasoline has more btu's of energy in it than does a gallon of ethynol, so the less ethynol you buy the better - if this is possible where you live.

You really sound like you know what your talking about. I already have changed the plugs, leads, fuel filter and cleaned my K&N. I was thinking about cleaning the Mass air sensor. I read on a post that when using a K&N filter, it is sometimes possible to overcoat the element, thus resulting in oil being sucked in and coating the sensors. I also read that the fuel pressure regualtor can give you bad economy but not affect the car's performance much and would certainly not show up on the computer (I think).
My Explorer had 100,000km on it when I changed all the above items. It now has 111,000km on it and I just did a service. I can't fault the car, it runs perfect. The engine is so smooth, you barely notice it is running. It still has plenty of power, but doesn't seem quite as powerful as it used to.
This Autotap sounds alright. What connectors can you buy to connect to the car? Where do you get the software? I have a spare computer which I will eventually have in my workshop. This might be the way to go.
The fuel I use, I'm told, does not contain any ethynol at all. We use Shell petrol. Come to think of it, my wife has recently been using fuel from a different service station. Seems like a coincedence that just recently we have been going through more fuel and using a different petrol.
Do you think it is worth having it scanned anyway? It might be a good idea to switch back to the other petrol and clean the air sensor. Then see what happens. Do you think I should change the O2 sensors anyway? I have a friend at Ford so I get things at cost.


Sounds like you have a good handle on that car already. It is true that when running an oil impregnated cotton filter (like K & N) those little mass air meter wires can become dirty from a little oil sticking to them. That mass air meter is very seneitve and a very little bit of oil or dirt can affect its performance. A dirty mass air sensor will surely affect engine performance. It's no big deal. Just disconnect battery, take K & N apart and spray with good electrical parts cleaner. You want to spray those two tiny little wires. They are fragile -- no high pressure air compressor cleaning.

I would consider changing your upstream O2 sensors. If you lay under your truck and follow your exhaust manifold out to the muffler, you should find a fancy looking spark plug with wires coming out of it threaded into the exhaust pipe. You should find one between the exhaust manifold and the catalytic converter and another one between the cat. converter and the muffler. You should find 4 total -- two on each side of the engine. These are your expensive O2 sensors that most folks never replace as they aren't cheap ($50 each at the parts house and $100 each at the dealer). The ones between the manifold and the cat. converter are the 'upstream' sensors. These are the ones the pcm uses to fine tune your engine as it is going down the road and are most important. The other ones between the cat. converter and the muffler simply are there to tell the pcm that there are indeed cats in place. Now the trouble with the O2 sensors is this: If one should fail completely your enginewill really run poorly and the pcm will set a hard code (check engine light). The pcm 'knows ' that if the O2 sensor's output voltage falls below a certain value the sensor has completely failed. In this case no problem O2 sensor has completely failed and needs replacement.....................but O2 sensors operate in some very harsh conditions, dealing with the high temperatures as well as the corrosive properties of exhaust gases. As the sensors age, they many times fail to react as quickly as they did when they were new. Thus the pcm isn't getting as good of information from the sensors as it did when they were new.

When your Ford engine is cruising down the highway and at proper operating temperature, your engine is running in 'closed loop' operation. Meaning the pcm is evaluating its different parameters -- intake air temp, coolant temp, engine load, O2 sensor readings, and many others. These pcms are programmed to keep the air / fuel ratio at about 14.62 : 1 for best fuel economy. When engine is under hard accleration, for example, the engine transitions into what is called open loop operation. Then, the pcm ignores O2 sensors and instead consults its own stored fuel table values and tunes the engine for hard acceleration - letting air / fuel ratio burn richer at say about 12.5 : 1...............................

So, as your O2 sensors age, their ability to quickly report changing conditions in the exhaust stream degrades -- just not enough to set a hard code (check engine light). And removing O2 sensor and testing it with a vom won't tell you how fast the sensor is reacting.

The problem, only in my opinion, is that I think Ford warrants their emissions control systems for 80,000 miles. If they recommended changing out those upstream sensors at say 35,000 to 40,000 miles they would be setting themselves up to replace them for free. See, catalytic converters could be working just fine and exhaust gases meeting emissions requirements, but since the O2 sensor is part of emissions system they would likely be forced to replace O2 sensors under warranty if they recommended changing them out to improve engine tuning and performance. I believe they would rather have engines getting less than optimal fuel economy and power than pay for O2 sensors. This is only my opinion.

If you decided to replace those two upstream sensors, buy Bosch. They are oem in many vehicles and were oem in my 98.

You can read up on diagnostic software at You plug into the obd II data port (standard by law in all late model vehicles). Then you plug in to your computer via usb port or serial port if you have an older computer. The diagnostic software takes very little computing power.

Sorry to get so long winded here, but the topic of tuning these Fords can become rather complex. I'm not a mechanic, but I have learned tons since I bought my 98, 99, and now 03 Fords.

Just curious, I assume you have the 4.0 soc engine. I had the 99 with the 4.0 ohv. It was great and got 20+ mpg with my mods. A real shame it got totalled.

Just an added note: some companies when selling their computer chips also require putting in a cooler 160 degree thermostat. All their doing is trying to 'cheat' the pcm into staying in open loop, rather than doing the proper tuning to actually increase with the actual engine parameters.


I have the 4.0litre SOHC engine. From my brief calculations, I'm getting about 14mpg maybe less in your terms. We use metric here in Australia so I can't be exact. I cleaned my Mass Air sensor this morning and re-cleaned my K&N, but this time making sure not to apply too much oil. It seemed to run ok afterwards, so I'll have to wait and see when this tank runs out. I might look into new O2 sensors aswell. Might be better to spend $$ on them rather than Ford. At least i'll know they are good.

Scanners for OBD2

A while Back I went thru the same exercise you are doing. I ended up with a program for my laptop from which is really great, and pretty cheap too. The documentation is pretty detailed but the program works good and I have solved a couple of problems with it so far on my 96 and 97 EBs. It's neat to drive down the road looking at graphs of data, like O2 sensors switching etc.They have a demo you can download to kind of try out. Give it a try. best Regards - Jerry ( a Ford kind of guy)