Is your CHECK ENGINE light on?....some tips
12-20-13, 09:27 AM
#1
Lexus Fanatic
Thread Starter
Is your CHECK ENGINE light on?....some tips
Although less-complex systems were also in use before then, ever since 1996, all new vehicles in the U.S. must have the OBD II (On-Board-Diagnostics) system to monitor emissions/engine-management functions and warn when something is not working properly. This sophisticated system monitiors dozens of different underhood, exhaust-system, and gas-filler functions and their associated sensors (mass-airflow sensor, crankshaft-position sensor, throttle-position sensor, spark-timing, etc....). When one or more of them is inoperative, not working properly, or out of factory-spec range, the computer turns on a (usually) yellow or orange-colored CHECK ENGINE light or symbol somewhere in the gauge-cluster. These symbol-shapes can differ somewhat from vehicle to vehicle when they are on and glowing, so check your specific Owner's Manual for reference. CHECK ENGINE lights/symbols being on are one of the most common issues that owners of newer cars often have to deal with.
Of course, when the light or symbol DOES come on, it tells you very little, right up front, about specifically is wrong, or what action has to be taken to correct it....and that is where some of the problems arise. I hope this will address some of them.
First, the system sometimes turns on the light for only a momentary or temporary malfunction (or just a momentary fluke in the circuits), and, though it doesn't always go off by itself immediately, will sometimes do so in a day or two, or after the computer has recycled/rebooted itself through one or more cycles of engine starts and stops. If the light then goes off, and stays off, then usually no other attention or service is needed.
Second, if the light does not go off, sometimes doing something as simple as tightening the gas cap a little will do the trick (assuming, of course, that it is not one of Ford's newer capless refueling systems). In fact, that is usually the first thing I recommend when people ask me what to do when the light comes on. That's because one of the dozens of sensors that the system monitors is for the vacuum created around the gas cap rubber O-ring seal...an EPA requirement to keep gas vapors from escaping into the air. As caps age, the rubber seals can get brittle or crack, allowing the vaccum seal to be broken. The sensor will report this to the OBD II's central computer, which will then turn on the light. Sometimes, unless the gas cap is really old and worn, just hand-tightening it a little more (don't overdo it) will do the trick, restore the seal, and turn the light off.
If that doesn't do the trick, then it may be time to take it to the dealer's service facility or other repair shop. Here's where many of the problems originate. The Service Technician will usually hook up an OBD II diagnostic scanner....in many cars, the plug/port for this is under the left side of the dash, near the hood release. The scanner will flash a diagnostic code to inform what system or circuit caused the problem. What some poorly-trained technicians or second-class repair shops do, though, sometimes, is just a knee-jerk reaction to the code by simply replacing the part or sensor that is is indicated in the code....oxygen sensor, spark plug, mass air-flow sensor, catalytic converter (converters can be expensive), etc......
That's not the way to do it. Simply doing that may or may not actually solve the problem..... and, if the vehicle is no longer under warranty, may end up costing the customer needless dollars in parts and labor. The correct way to do it (Pat Goss, the head Technician on TV's Motorweek, who also owns his own repair shop, has described this many times in detail) is for the technician, when the scanner indicates a code, to consult the factory Technical Repair Manual for the vehicle/engine (which, of course, was written by the engineers who designed the system) and then do a series of further diagnostic tests that are first required by the code. This, of course, may take a little more time (and with a lot of shops, they are in a hurry and don't want to take the time). But, if done correctly, it may or may not require an actual part or sensor-replacement....sometimes only requiring a less-expensive option as a minor adjustment.
Of course, when the light or symbol DOES come on, it tells you very little, right up front, about specifically is wrong, or what action has to be taken to correct it....and that is where some of the problems arise. I hope this will address some of them.
First, the system sometimes turns on the light for only a momentary or temporary malfunction (or just a momentary fluke in the circuits), and, though it doesn't always go off by itself immediately, will sometimes do so in a day or two, or after the computer has recycled/rebooted itself through one or more cycles of engine starts and stops. If the light then goes off, and stays off, then usually no other attention or service is needed.
Second, if the light does not go off, sometimes doing something as simple as tightening the gas cap a little will do the trick (assuming, of course, that it is not one of Ford's newer capless refueling systems). In fact, that is usually the first thing I recommend when people ask me what to do when the light comes on. That's because one of the dozens of sensors that the system monitors is for the vacuum created around the gas cap rubber O-ring seal...an EPA requirement to keep gas vapors from escaping into the air. As caps age, the rubber seals can get brittle or crack, allowing the vaccum seal to be broken. The sensor will report this to the OBD II's central computer, which will then turn on the light. Sometimes, unless the gas cap is really old and worn, just hand-tightening it a little more (don't overdo it) will do the trick, restore the seal, and turn the light off.
If that doesn't do the trick, then it may be time to take it to the dealer's service facility or other repair shop. Here's where many of the problems originate. The Service Technician will usually hook up an OBD II diagnostic scanner....in many cars, the plug/port for this is under the left side of the dash, near the hood release. The scanner will flash a diagnostic code to inform what system or circuit caused the problem. What some poorly-trained technicians or second-class repair shops do, though, sometimes, is just a knee-jerk reaction to the code by simply replacing the part or sensor that is is indicated in the code....oxygen sensor, spark plug, mass air-flow sensor, catalytic converter (converters can be expensive), etc......
That's not the way to do it. Simply doing that may or may not actually solve the problem..... and, if the vehicle is no longer under warranty, may end up costing the customer needless dollars in parts and labor. The correct way to do it (Pat Goss, the head Technician on TV's Motorweek, who also owns his own repair shop, has described this many times in detail) is for the technician, when the scanner indicates a code, to consult the factory Technical Repair Manual for the vehicle/engine (which, of course, was written by the engineers who designed the system) and then do a series of further diagnostic tests that are first required by the code. This, of course, may take a little more time (and with a lot of shops, they are in a hurry and don't want to take the time). But, if done correctly, it may or may not require an actual part or sensor-replacement....sometimes only requiring a less-expensive option as a minor adjustment.
Last edited by mmarshall; 12-20-13 at 09:40 AM.
12-20-13, 12:11 PM
#2
Lexus Champion
I thought this was great info from Autozone (which will diagnose your check engine light for free btw)......
http://www.autozone.com/autozone/lan...k-engine-light
http://www.autozone.com/autozone/lan...k-engine-light
12-20-13, 06:00 PM
#4
Lexus Fanatic
Thread Starter
Thanks. 
I've posted them both from personal experience and what I've learned from others.
Same here. One of these days, I just MIGHT learn how to use BMW's I-Drive and Audi's MMI....but don't count on it. 
I've posted them both from personal experience and what I've learned from others.
Usually just a refresher for me but once in awhile I learn something new 
Last edited by mmarshall; 12-20-13 at 06:13 PM.
12-21-13, 08:55 AM
#5
Out of Warranty
Great notes, Mike! Once in a while the solution to an intermittent problem may never throw a CEL, but will still leave a trail of bread crumbs in the OBD.
Last spring a miss on #3 cylinder in the minivan would only appear occasionally - never enough to turn on the check engine light - had finally become regular enough to chase down. I figured it was a bad plug, but the guys at AutoZone read the codes, found several other possible problems and offered some good advice: when presented a list of likely causes, start with the cheap solutions. OK, plug, plug wire, distributor cap and remaining wires, crank position sensor . . .
I'd been dreading this because on the MoPar minis the engine sits behind the front axle, and the ignition system is so far back under the cabin air intake, it's nearly in the front seat. I'd tried to get at it without removing body panels, but with my big mitts it was a guaranteed knuckle-buster, even with a new set of double-jointed wrenches to get at the plugs and distributor. I noticed that the #3 plug wire was bent into a tight "S" - not a good sign . . . somebody had trouble with this before. Uh-oh.
I finally took it down to my local garage where the owner's teenaged son, who is blessed with tiny hands was able to get in there, remove the plug wire, and extract the #3 plug easily. The side electrode was burned and the central electrode was almost non-existent. At 95K that plug was probably OEM since it was so difficult to reach. unlike the points-and-coil ignition, modern flamethrowers can produce one heck of a spark, even enough to bridge a huge air gap created by a badly burned plug. That can lead to complacency. We don't change plugs every 10-15K like we once did . . . and because most can survive 50K, we sort of erase them from our "to do" maintenance charts. Of course the fact that plugs are not easily serviceable on modern engines doesn't help. Out of sight, out of mind.
While the kid was in there I had him change all the plugs and a install proper #3 wire that was of the appropriate length. Problem fixed. No further codes. The little 2.4L hums along contentedly.
Last spring a miss on #3 cylinder in the minivan would only appear occasionally - never enough to turn on the check engine light - had finally become regular enough to chase down. I figured it was a bad plug, but the guys at AutoZone read the codes, found several other possible problems and offered some good advice: when presented a list of likely causes, start with the cheap solutions. OK, plug, plug wire, distributor cap and remaining wires, crank position sensor . . .
I'd been dreading this because on the MoPar minis the engine sits behind the front axle, and the ignition system is so far back under the cabin air intake, it's nearly in the front seat. I'd tried to get at it without removing body panels, but with my big mitts it was a guaranteed knuckle-buster, even with a new set of double-jointed wrenches to get at the plugs and distributor. I noticed that the #3 plug wire was bent into a tight "S" - not a good sign . . . somebody had trouble with this before. Uh-oh.
I finally took it down to my local garage where the owner's teenaged son, who is blessed with tiny hands was able to get in there, remove the plug wire, and extract the #3 plug easily. The side electrode was burned and the central electrode was almost non-existent. At 95K that plug was probably OEM since it was so difficult to reach. unlike the points-and-coil ignition, modern flamethrowers can produce one heck of a spark, even enough to bridge a huge air gap created by a badly burned plug. That can lead to complacency. We don't change plugs every 10-15K like we once did . . . and because most can survive 50K, we sort of erase them from our "to do" maintenance charts. Of course the fact that plugs are not easily serviceable on modern engines doesn't help. Out of sight, out of mind.
While the kid was in there I had him change all the plugs and a install proper #3 wire that was of the appropriate length. Problem fixed. No further codes. The little 2.4L hums along contentedly.
Last edited by Lil4X; 12-21-13 at 09:00 AM.
12-21-13, 09:19 AM
#6
Lexus Fanatic
Thread Starter
I finally took it down to my local garage where the owner's teenaged son, who is blessed with tiny hands was able to get in there, remove the plug wire, and extract the #3 plug easily. The side electrode was burned and the central electrode was almost non-existent. At 95K that plug was probably OEM since it was so difficult to reach. unlike the points-and-coil ignition, modern flamethrowers can produce one heck of a spark, even enough to bridge a huge air gap created by a badly burned plug. That can lead to complacency. We don't change plugs every 10-15K like we once did . . . and because most can survive 50K, we sort of erase them from our "to do" maintenance charts. Of course the fact that plugs are not easily serviceable on modern engines doesn't help. Out of sight, out of mind.
While the kid was in there I had him change all the plugs and a install proper #3 wire that was of the appropriate length. Problem fixed. No further codes. The little 2.4L hums along contentedly.
While the kid was in there I had him change all the plugs and a install proper #3 wire that was of the appropriate length. Problem fixed. No further codes. The little 2.4L hums along contentedly.
Today's plugs, as you note, can easily go 30-50K...even 100K in some cases for platinum plugs. But, the problem is......if they actually stay in the block that long, sometimes the accumulated engine heat over the years burns the plug-threads into the block so hard it is very difficult to actually remove them, even though they usually put them in with anti-seize compound at the factory. I've heard of cases where the technician actually had to drill them out and repair/rethread the block or cylinder head.
12-22-13, 01:02 AM
#7
Consulting the factory service manual should be the 1st step in any repair IMO. I know for GM cars they are CHEAP(like $20). For Toyotas, cheapest I could find for my 93 truck was $120(and I paid $550 for the whole damn truck lol).
Also, on pre 1996 cars with OBD I, there is a way to read the codes without a scanner. You turn the igintion to on, bend a paper clip, and insert the two ends into a certain port on the connector under the dash. This grounds the PCM and puts it into diagnostic mode. It makes the PCM flash the check engine light a certain number of times. You count the flashes, then consult the factory service manual for the code. Then look up the code, it tells you how to fix the problem. My 91 Cadillac Brougham had a whole 10 page section on how to do this, saved me a ton of $$$$ when that check engine light came on a couple of different times.
Also with certain model Cadillacs(might also apply to other luxury cars), you push a certain sequence of buttons on the dash(usually temp up and fan max) and the in dash display will read you recent trouble codes.
Also, on pre 1996 cars with OBD I, there is a way to read the codes without a scanner. You turn the igintion to on, bend a paper clip, and insert the two ends into a certain port on the connector under the dash. This grounds the PCM and puts it into diagnostic mode. It makes the PCM flash the check engine light a certain number of times. You count the flashes, then consult the factory service manual for the code. Then look up the code, it tells you how to fix the problem. My 91 Cadillac Brougham had a whole 10 page section on how to do this, saved me a ton of $$$$ when that check engine light came on a couple of different times.
Also with certain model Cadillacs(might also apply to other luxury cars), you push a certain sequence of buttons on the dash(usually temp up and fan max) and the in dash display will read you recent trouble codes.
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