Answer:   This is a difficult problem to detect because the computer can not sense a malfunction, the vehicles computer system thinks everything is ok. In reality what is happening is the electrical component inside the MAF sensor becomes contaminated by air impurities. These containments imbed themselves to the electrical component that senses the air flow causing the sensor to be slightly off, but not enough to trigger the MIL (malfunction indicator lamp). Replace the MAF sensor with a new. NOTE: (Mass Air Flow MAF sensor or Air Intake Sensor AIS, depending on manufacturer. It does the same thing only with different names).

Question: 2004 Ford Ranger mileage: 47,000. The engine light keeps coming on and the computer reads EGR valve, but I already had that replaced. What do you think could be the problem?

Follow-up: I sent you a question but have since found out my problem. The problem was the pressure feedback exhaust sensor ($88.23). The place I took it to said he has had to replace that thing in every Ford Ranger he's seen. It stopped my problem! I thought it might be informative to your readers!- THANKS 2CarPros.com !

Question: 1999 Mazda Protege mileage: 88,000. My car recently tripped the engine check light. My wife took the car to our local Mazda dealer (I was out of town) and they pulled codes 23 and 24 from the computer. According to the service manager, those codes related to high idle and misfire. Anyway, all they did was adjust base idle, perform a top end carbon cleanout, and reset the computer. According to the service report, they road tested the car for about 9 miles and the check light stayed out. When my wife picked up the car, she drove it a short distance away from the dealer and, as you might expect, the check light came on again. I'm perplexed. I did a bit of Internet research yesterday after the car visited the dealer and my information indicates that codes 23 & 24 relate to the right side oxygen sensor, not high idle and misfire. All the various engine sensors are original. Also, plugs are new NGKs and we do use high octane gas as recommended by Mazda. My speculation is that the oxygen sensor is bad. With 128,000 miles on the car, it appears prudent to me to replace both the right hand and left hand sensors. Am I heading in the right direction?

Answer: Replace that oxygen sensor. If the spark plug wires are several years old, replacing them would be a good idea. If the problem persists, you may have to replace the mass airflow sensor.

Answer: If you scan the computer for fault codes, it should tell you which component is faulty. Replace as needed to recheck system.

Question: 2000 Toyota Camry 2.4 mileage: 149,000. I went to change my oil and the guy at the shop asked me if I wanted to clean my injectors because this is due at 50,000 miles. I said ok, let's do it because I really take care of my car and want it running good. The guy connected a little pressurized bottle to my engine through a coiled yellow tube, and started the engine, revving it up slowly. After about 10 minutes and a lot (I mean a LOT) of smoke/steam coming out of the tail pipe, he decided that the injectors are clean. I paid 60 bucks for this. The problem is that the yellow "check engine" light came on after I started my car to go home. Went back to the shop immediately and asked the mechanic what's going on. He told me that the light is going to go away by itself after 1-2 days of driving and that this thing it's normal after cleaning injectors. So after 2 days the yellow light is still on. Is it going to go away by itself? The car works just fine but I really don't like having that yellow light on all the time.

Answer: The check engine light means that there is a fault code stored in the computer. If the computer is scanned, it will tell you which component is causing the light to go on.

Question: 2000 Mazda Protege 1.8 mileage: 17,000. After re-fueling, my check engine light stayed on and the O/D light was flashing. I stopped, shut off and restarted the car and just the check engine light remained on. I re-seated the gas cap, to no avail. I was running on fumes before refilling; it took 14.2 gallons in a 14 gallon tank. Is there a reset button/procedure somewhere?

Answer: Once the check engine light comes on due to a loose or missing gas cap, the computer must be reset with OBD-2 scanner after the cap is re-secured.

Answer: Do a compression check on all cylinders. Make sure that all spark plugs and plug wires are in good condition. The computer must be reset with OBD-2 scanner after repairs have been performed.

Answer: The code you mentioned indicates a problem in the fuel vapor recovery system. Check for a loose case cap, cracked or loose vapor hoses, faulty purge relay or purge solenoid. The module is probably alright.

Answer: The camshaft sensor tells the engine control computer the position of the camshaft. Our flat rate labor guide shows the time to change the cam position sensor at 36 minutes on your car.

Answer: The dealer did not know what was causing the check engine light to come on. When the computer was scanned, it showed a fault code in the fuel evaporator system, which led the mechanic to the area of the gas cap. The dealership spent time locating your problem but obviously, a gas cap that was not tightened properly is not covered by warranty and thus the dealership could not look to the manufacture for reimbursement.

Answer: Check all the fuses. In addition, check for voltage to the oxygen sensor heater.

Question: 1997 Ford Taurus GL 3.0 mileage: 121,000. The check engine light came on and a local mechanic told me it was a faulty crank sensor. I bought the part and sure enough, my old sensor was broken inside. After cleaning out the broken pieces, I put in a new sensor. However, the check engine light is still on. I gather from reading your site that I may need to have the computer rescanned and/or cleared. Is this so? Is there a reset button I can push? Or do I need someone with a device to clear the computer?

Answer: There is no reset button that can be pushed. The check engine light must be reset with an OBDII computer scanner.

Question: 1999 Hyundai Accent GSI 1.5 mileage: 49,000. My Check engine light comes on intermittently. It will come on for a couple of hours or for a day but then goes out. There is no performance loss or any obvious problems with the vehicle. Is there a way to check what is causing this without returning to the dealer?

Answer: Yes there is. Any vehicle service center that has an OBDII scanner can scan your vehicle and identify the stored fault codes.

Question: 1993 Pontiac Grand Am V6 mileage: 110,000. What might cause the check engine light to come on when you are driving at highway speed and then let off the gas? You can drive for varying distances but the first time you let off the gas the CEL comes on. If you decelerate (close the throttle) very slowly you can keep the light from coming on. I want to try to check the codes but the printout on the connector under the steering wheel doesn't match other diagrams I've seen. As you look at it from the drivers seat, it has 2 rows of six pins. There is one pin in the top right of the connector and two pins in the lower right of the connector. The connector alignment tab is on the top. This would equate to pins A, K, & L from other diagrams I've seen.

Answer: On pre-1995 cars you could jump between two of the pins and read the codes that were stored in the computer. 1995 and newer cars require the use of the OBDII scanner to retrieve the codes.

Question: 1996 Cadillac Sedan DeVille mileage: 101,500. During warmer weather (above 48 degrees F) the fuel data center will start cycling sporadically through the various displays. The "Change Oil" light will flash on and off during this event. Eventually, the ECM and BCM will start throwing codes such as Data signal lost between BCM and Data signal lost from ECM. Without spending hundreds of dollars buying new ECM's, BCM's, and Fuel Data Centers, have you ever heard of this occurring on this make and model of vehicle before? If so, what is the procedure for diagnosis and what is the repair made to it? (This one has thrown me!)

Answer: Check the ground wires for proper connections (resistance). Also, see if you can duplicate the problem by moving the wiring looms and watching the display. Check the looms for damage and/or corrosion on the connectors.

Question: 1993 Ford Aerostar 4.0L mileage: 92,000. Check engine light comes on after backing off the gas pedal at about 45 or 50 mph. But then, touch the gas pedal and the check engine light goes off. Code says lean fuel/air to right rear bank. This van DOES NOT have an EGR nor a MAPS. So far, Oxygen sensor, air filter, and fuel filter have been changed. In addition, it has been de-carboned. When passing gear is engaged it feels like it is "gagging". Any suggestions?

Answer: You may have a partially plugged fuel injector or a vacuum leak. In addition, do a compression check on the engine.

Question: 1999 Chrysler LHS mileage: 72,000. Check engine light is on, idles rough. Had the car in the shop and they gave me a long laundry list of about $900 worth of stuff to fix which included, fan belts, timing belt, and water pump. In May the timing belt broke, so we had that replaced, along with the water pump. The code when you do the key thingy, says O2 sensor. This car had 4 of them, at about $90 each. I picked the cheapest one of them and replaced it. Unplugged the battery and it went out for about 2 weeks. Now it is back on. My question is this: the car runs fine other than the rough idle, will one of the O2 sensors being bad cause my problems? Is there any easy way to check them without paying an arm and a leg?

Answer: A bad oxygen sensor will cause an engine to run poor. If you have the computer scanned, it will tell you which of the oxygen sensors has failed.

Question: 1997 Isuzu Rodeo 3.2L V6 mileage: 65,000. My wife was driving her '96 Rodeo 3.2L V6 and the speedometer quit working. Oddly enough, the CHECK ENGINE light came on about 2 minutes later. When she restarted the CHECK ENGINE indicator came on immediately. I pulled the ECM fuse to reset the computer and drove the car for a few minutes. The CHECK ENGINE light did not come on, but the speedometer still doesn't work. Should I be thinking loose connection (already looked and didn't find any), faulty ECM, or the unlikely coincidence of speedometer failure combined with failure of another component that would trigger CHECK ENGINE?

Answer: Your computer needs information from the speedometer signal to properly manage the engine. When your speedometer quite working, the check engine light did what it was supposed to do. You need to get the speedometer working again and then clear the codes from the computer.

Question: 1997 Mitsubishi Eclipse liter mileage: 101,000. Dear Bob and Ken, I just purchased a 91 Eclipse and while driving it home the check engine light came on. I took it to the shop and they scanned the engine and came up with a code 14. Throttle position sensor was the problem. The only problem I have had with the car is it shifts slowly and sometimes jerks when it does. The car is an automatic. Are the mechanics right with their diagnosis? Or could the problem lie somewhere else? Thank you for your time. Jeanice

Answer: The throttle position sensor tells the computer how far open the throttle is. This does affect the transmission shift points. Your mechanic appears to be on the right track.