Any auto repair experts? Question regarding 'check engine' light

Jon_Are

Senior HTF Member
Joined
Jun 25, 2001
Messages
2,036
What's the scoop on the 'check engine' light? The last few cars I've owned have had a problem with the light staying on, and - after several trips to the shop - the problem usually remained unresolved. Friends and relatives tell me similar stories.

Now yesterday, the light came on in my '98 Ranger (35,000 miles). Took it in this morning to a shop I've come to trust. Picked it up a few hours ago - after paying a $48 charge for analyzing the engine - and found that the light is still glowing as before. The bill states "Code for mass air flow sensor low reading, cleaned & reset." The mechanic had already gone home; I'm going to call him in the morning.

So...WTF? Are these lights worth paying attention to? I hate to bring it back in, probably repeatedly, while the engine analyzer spits out different codes and the mechanic chases a problem that may not even exist.

Should I bring it back in? (note: the truck hesitated on acceleration a few times when the light first came on, and once more on the way home from the shop, otherwise rode fine. Never had any problems at all before.) Or should I live with the freakin' thing?

Thanks,

Jon
 

Eve T

Supporting Actor
Joined
Jan 16, 2002
Messages
616
If you had problems with it on the way home I would take it back in. Did you ask what their analysis was for the check engine light coming on? Could be a loose wire making it stay on that keeps making a connection I'm really not sure but could ask a mechanic buddy of mine. About the problems you had on the way home... sounds like that could be a timing problem or perhaps your distributor. I'd mention that to them when you take it back (and I would take it back) to find out why they "think" the light is staying on and to address the problems you had on the way home.

I'm not a mechanic but I turn wrenches on my car and work as a parts monkey at a parts store at night.

Good luck

Eve
 

Len Cheong

Second Unit
Joined
Mar 18, 2000
Messages
372
Sometimes, if you did not screw the gas cap on tightly enough, the check engine light will come on. After you rescrew it on tightly, it usually takes a day before the check engine light goes off again. Happened to me once.
 

Brad_V

Second Unit
Joined
Mar 8, 2002
Messages
356
I would have thought the shop would have called you and asked if you wanted the mass air sensor replaced, etc, instead of just checking the code and having it come back on.

Used to be, the CE light would come on mainly only for an emissions problem, so it didn't matter a whole lot. Now it can point to a serious trouble spot.

If you've had previous cars with CE problems that were never figured out by the shop, I'd find a new shop. Seriously.

Oftentimes, a car will run bad when a sensor is having a problem, but then when it gets bad enough to trip the CE light, the computer will switch that output to a standard setting and bypass that sensor, and then the car will run much better. It won't run like it should, but will run much better than before the CE light came on and the sensor was going out. That's probably why yours ran better once the light came on. It flagged the code and then switched to the default setting for that sensor.
 

Jon_Are

Senior HTF Member
Joined
Jun 25, 2001
Messages
2,036
Someone tell me about this sensor...where is it located? What, specifically, does it sense? How can one sensor (I assume there's just one) indicate so many different problems?

Eve: I couldn't ask about the analysis, the mechanic had gone home. I will today. Go ahead and ask your mechanic friend, I'd appreciate it.

Brad: The truck hesitated after the light went on for the first time, and again after they 'fixed' it.

I just don't want to keep emptying my wallet each time they find a new 'solution'.

Thanks, everyone,

Jon
 

AllanN

Supporting Actor
Joined
Mar 15, 2002
Messages
950
Funny I have a 2000 Ranger with 32k on it and the CE light has been comming on randomly. It runs a little rough when it is on so I think its eitehr the MAF Sensor or the O2 sensor. Although they should not have charged you anything because it under warenty. I had the Oil Pressure sensor go and the truck would not start and they fixed it for free.
 

SteveA

Supporting Actor
Joined
May 25, 2000
Messages
700
I have a friend who works in the service department of a large car dealership - and the number one complaint his shop receives is: "My check engine light is on in my Ford!"

Apparently, it's a problem that absolutely plagues late model Fords.
 

Vince Maskeeper

Senior HTF Member
Joined
Jan 18, 1999
Messages
6,499
The CE light is a simple indicator for all the computer monitoring systems in a modern automobile. Like was mentioned above- early version really only monitored emissions and vacuum issues- but modern ones have sensors all over the car, in every major system that monitor air flow, valves, fuel, every kind of pressure, etc.

In the old days, on most models you could do a "blink back" by bridging two pins - the CE light would blink out a code number which diagnosed the problem, and you just have to look it up in a book. These days, I think this has been disabled (to prevent driveway mechanics from actually working on their own cars, and to require professional mechanics to actualy purchase the very expensive diagnostic software).

Too bad, I used to use the blink back on my Buick to save a trip to the dealer.

-Vince
 

Chet_F

Supporting Actor
Joined
Mar 1, 2002
Messages
776
Typically from my experience the CE light comes on if your oxygen sensor is faulty. But I suppose that the CE light can be programmed to show status of many problems. The oxygen sensor usually does not fail until 50-60k miles so I would rule that out in your case. It is possible that your specific car has problems related to your CE light that may be found on the net. Do a search and crossreference with the type of vehicle and CE light to see if you can find a correlation of a specific problem with mileage. I also would recommend looking at newsgroups as a reference tool.
Good Luck
 

Jay H

Senior HTF Member
Joined
Mar 22, 1999
Messages
5,654
Location
Pittsfield, MA
Real Name
Jay
I doubt it's just Fords, many problems result in the magical "check engine" light to show up, some things like the gas cap isn't entirely obvious. It's kind of the blanket solution to any problem, kind of like the blue screen of death for Microsoft Windows users. But then these days with OBDII and stuff, it's hard to diagnose stuff without fancy electronics and software so the "check engine" light is perhaps the only reasonable solution for auto makers. Many of the luxury cars have specific sensors for the various fluids, even the brakepad wear, but still they are not exempt from the "check engine"-syndrome.

I know many cars have hidden diagnostic menus, but you need somebody to tell you what each code means, which you can usually find on the net.

Jay
 

Todd Hochard

Senior HTF Member
Joined
Jan 24, 1999
Messages
2,312
The mass air flow sensor is a metal cylinder in the intake air path. It's located between the air filter and throttle body (maybe not physically, but speaking in terms of the air path). Its job is to sense the amount of air moving into the engine. From this (and other parameters), it can calculate injector duty cycle (i.e. how much fuel into the engine), and spark advance. It is one the KEY sensors in any fuel injected engine.
MAF sensor low reading? Hmmm... when was the last time you changed the air filter? Does it tend to hesitate more under acceleration, or also when cruising?
The check engine light is your friend. The shotgun-style troubleshooting that your mechanic uses is not. Don't blame the electronics- it can only report the symptoms. A GOOD technician will consider ALL symptoms and possibilities, and attempt to get to the true source of the problem.
Todd
P.S. The check engine light has never been on in my '95 Accord. 112K miles and NO parts failures yet.
 

TimG

Second Unit
Joined
Oct 5, 1999
Messages
361
I would have to agree with Todd, check your air filter. A lot of the newer cars will also use the light to signal time to take it to the dealer for service. My wifes Volvo does this at predetermined intervals. All they do is use a "doohickey" to reset the light. The hesitation may just be a coincidence, (clogged fuel filter?) if you are lucky. I will tell you a Mass Air Flow Sensor is not cheap to replace. (Replaced one on my wifes old 86 Volvo) Good luck.

Tim
 

Jon_Are

Senior HTF Member
Joined
Jun 25, 2001
Messages
2,036
Update time.
The mass air flow sensor has been replaced, to the tune of $200. So far, the truck runs beautifully. According to the mechanic, they knew this was the problem, but sometimes they can simply clean it out and it would function. If not, replacement is indicated. Would have been nice to know all this from the get-go, though.
Todd: Excellent explanation. The mechanic explained much the same stuff to me and showed me my defective sensor.
Vince: You've impressed me previously with your HTF knowledge, and now again with cars. You some kinda know-it-all or something?

Jon,
fondly recalling the days I used to do my own work on cars...gapping plugs, checking timing, etc. Nowadays, you're lucky if you can even get access to the plugs.
 

Leroy

Second Unit
Joined
Jun 30, 1997
Messages
305
My 2002 Ranger not only has a check engine light, but the overdrive light also doubles as a trouble light for the drivetrain. My O/D light came on 2 days after delivery and it was because the transmission fluid was a little low. To the dealer a couple of days to figure that one out.

I know that the check engine light on my old Mitsubishi came on at preset intervals to remind the owner of scheduled maintainence.
 

DennisHP

Second Unit
Joined
Aug 6, 2000
Messages
352
Next time your CE light comeson, dis-conect the battery and then re-connect it. It will reset the car's computer and sometimes the lights will stay out if there is not a serious problem.

On some vehicles there is a sequential procedure performed with the key in the ignition (turn the key on then off a couple times while holding your mouth a certain way) that will return the problem code that you then reference in a manual that will tell which device is having the difficulty.
 

Jon_Are

Senior HTF Member
Joined
Jun 25, 2001
Messages
2,036
Good advice on the battery disconnect, Dennis. I'll remember that.

Those coded procedures are too mysterious and time-encompassing for me to deal with. I'm a guy who hates Easter eggs.

Jon
 

Bill_Weinreich

Second Unit
Joined
Sep 25, 2000
Messages
317
One problems with CEL's is that since about '96, the federal govt mandated all vehicles in the US to comply to the OBDII (On Board Diagnoses Series 2) standards. This sets a good protocal in the fact that all vehicles have the same connection (also in about the same place on the vehicle), the generic codes can be read by a single type of scan tool, all terminology is to be the same (i.e. computers used to called ECM, PCM, SMEC, .... now they fall under one title) The problem sometimes lies in the fact that all the manufacturers have to adapt their computers to be compatible. Not unlike your PC at home, compatibility is always an issue. Also some manufacturers will still use other self diagnoses systems (in addition to OBDII) that only specialized scan tools can read.

The CEL on an OBDII vehicle will usually stay on after a trouble code is set, even if the problem goes away. Hence a harder diagnoses.

Disconnecting the battery on these vehicles will not always clear the codes. Sometime it has to be done with a scan tool.

On some vehicles there is a sequential procedure performed with the key in the ignition (turn the key on then off a couple times while holding your mouth a certain way) that will return the problem code that you then reference in a manual that will tell which device is having the difficulty.
- Pre OBDII Chrysler products.

Bill

Oops, One more thing about the gas cap.
Yes a loose gas cap (or a bad one) can set a DTC (Diagnostic trouble code) also remember that it can set when fueling the car with the engine running.
 

Joe Tilley

Supporting Actor
Joined
Jan 1, 2002
Messages
686
I'm probley repeating something someone else said (I didn't read everyones replys) But if you disconnect your battery for about 5 minutes then re hook it it will clear any saved trouble codes & turn off the CE light. It is very easy to check these codes your self if you wont,most newer cars have an ALCL link under the drivers side of the dash that by jumping two certain terminals & than turning you key to the start pos will make the CE light flash a code stored in the ECM. You can get a Haynes manual to get the codes & what terminals to jump to find out what is going on.

Normally it is something pretty simple like a 02 sensor,throttle position,or EGR,all things that are very easy to do yourself if you have some basic hand tools & a good set of rubber arms to get to the problem sensor.

I wouldn't bother with a dealer unless it a warranty thing or unless you absolutely have no way to do it your self.
 

Henry Carmona

Screenwriter
Joined
Feb 7, 2000
Messages
1,299
Location
San Antonio
Real Name
Henry Carmona
If the MAF was dirty, you could have cleaned it.
Im not sure about Rangers, but my truck also has a screen on the MAF that can trap fibers, etc. and clog up.

If it was malfunctioning, then there was nothing you could do besides pay up.

Be prepared to replace your O2 sensors in a few thousand miles. they arent cheap either. I replaced my sisters on her Ranger not long ago.
 

Forum Sponsors

Forum statistics

Threads
345,174
Messages
4,733,132
Members
141,399
Latest member
Industrious