Archive for May, 2009
Check Engine Light – Code Readers
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If you see a “check engine” or a “service engine soon” light in your instrument cluster; your car has stored a diagnostic trouble code. Which means the computer system on your vehicle has detected a problem within various systems it controls. Your car has many different sensors that monitor the various vehicle systems.
If the trouble code light has been illuminated then your vehicle enters into a “limp mode” . This means it is running on a program that causes poor mileage and increased emissions.
To find out what trouble code or codes were stored then you must use a code reader or Scan Tool . Most scan tools will tell you all of the codes that are stored in the PCM and most of the time in the order they were stored.
Now if you plan on working on your own vehicle quite a bit then I highly recommend paying for a subscription to www.alldata.com. Its one of the best web sites for the do it your selfers and they supply a lot of info that you cant get any where else. It will cost you about $ 26.00 dollars for your first vehicle and $ 16.00 for every vehicle after that and the subscription lasts for one year. Its well worth it and they give you all the TSBs or Technical Service Bulletins, Which are very helpful in diagnosing your problem.
First locate your vehicle’s computer connector (ALDL) or Data Link Connector , most are on the lower driver’s side. In some vehicles you might need to look around a little, on the passenger’s side, and around the center console under a plastic cover. For more information, check your owner’s manual.
After repair has been made, clear the trouble codes and re-check system. After codes have been cleared the computer system is ready for internal testing, this means that while the car or truck is in operation and the on board computer is performing tests. These tests are called “monitors” and most cars have between 4 and 8 monitor systems. The computer goes through its testing procedure in about 40 to 60 miles.
Most on Board Computers are called ECMs ( Electronic Control Modules ) or on the 1996 and newer models they are called PCMs ( Powertrain Control Modules ) and they usually look like this. The job of the ECM or PCM is to monitor the input and output signals produced by various sensors in the system. The ECM or PCM then adjusts the system as necessary.
Sensors can include: oxygen sensor, coolant sensor, mass air flow sensor, air intake sensor, crankshaft angle sensor, throttle position sensor, camshaft angle sensor and knock sensor. The ECM operating program consists of information cells. These cells hold the code for proper engine operation, if information is outside the cell parameters, a MIL (malfunction indicator lamp) or “check engine light” is illuminated on the dash.
Once a “check engine” or a “service engine soon” light in your dash has illuminated, the ECM has stored at least one diagnostic trouble code. This means the computer system on your vehicle has detected a problem with the various systems it controls. Your car or truck has many different sensors that monitor the various vehicle systems.
If the trouble code light has been illuminated your vehicle enters into “limp mode” this means it is running on a special program that causes poor mileage.Trust me if you are running on “limp mode” it will feel like your car is about to stall.
The ECM outputs a 5 volt reference to most sensors to drive the monitoring circuits. The ECM also controls the radiator cooling fan, air pump controls, fuel pump, EVAP system and more depending on the vehicle.
Manufacturers have different trouble codes for each vehicle and some can be very generic. Check with a good after market repair manual if your code reader cannot give you the definition of your code so you can know where to start looking.
And remember that a code definition doesnt mean that a specific sensor is bad. Check it out before replacing it or you could be throwing your money away.
Well I hope this has answered a few questions about that mysterious “ Check Engine Light “ and if you have any more questions, I would like to hear from you. Just leave a comment by clicking on the contact us tab at the top of the page and I will try to answer it for you as soon as possible.
Until next time , this is ASE Master Mechanic Jeff Williams saying ” Thanks for Stopping By ” and if this web site has been helpful to you then please help us keep it running by clicking on the coffee cup icon below. Your support is greatly appreciated. Jeff
CV Axles-Description and Replacement Info
Posted by: | CommentsFor most of you that have worked on a front wheel vehicle the image you see below is nothing new, but for the people out there that have never seen one of these things before, it is called a CV ( Constant Velocity ) axle or more commonly known as a Half Shaft.
A CV joint or constant velocity joint is a type of mechanisms that connects two fixed rotating shafts. This joint allows the shafts to be connected while axis’s pivots change, for example when suspension or steering operation occurs. CV joints are widely used in front-wheel and rear wheel drive cars.
CV joints can deliver torque more evenly then conventional “U” joints. The CV joint is used because of its ability to transmit more even torque throughout a particular flex range. A CV joint can also deliver power on a wider range of angles then “U” joints which makes them more desirable then its older counterpart.
The CV joint is virtually non-serviceable unless the boot ruptures or extreme conditions exist, like high mileage or abuse. When the CV joint fails simply replace it with a new unit.
A CV Half Shaft is composed of four basic pieces. They are the inner joint or inboard shaft , the outer joint or outboard shaft, the axle and the axle nut. Both inner and outer joints have a protective rubber boot on them that can sometimes tear, which is why most half shaft fail in the first place.
If you were to open the inner and outer joints up, chances are they would look like this on the inside. There are those who like to rebuild the joints and replace the boots but due to economical reasons, I prefer to replace them.
For those of you that are curious as to why I say that, I have a few illustrations below that give you the very basics of Boot Replacement.
The Boot itself is very inexpensive but when it fails the entire half shaft is prone to fail as well. The job of the Boot is protect the bearing assembly inside from the outside elements while holding in life giving grease.
The Boot closest to the wheel is always prone to tear or split first due to them experiencing the most movement.Once the boot tears or splits, grease is thrown out of the joint by centrifugal force while driving. Without grease to keep the joint lubricated and cooler, its life is drastically reduced.
If you own a front wheel drive vehicle, look under it and check out your boots for signs of tearing . It should be easy to spot. If so, then its only a matter of time before the fail. Once they fail, your vehicle will no longer move in any direction.
The most common sign that your CV joints are about to fail is by the clicking sound they make when you make a turn. You only have a short while before you the bearing fail and the shaft is no longer connected to the outboard joint.
Removing the Half Shaft Assembly :
The job of removing the Half shaft on most cars is pretty much the same on all cars. Below is a quick list of how to do it, but please consult your repair manual for a more complete guide to replacing your own half shaft.
1. Remove the front wheels
2.Remove the big nut that holds the joint to the wheel hub. ( You may have to replace it with a new one on some models )
3.The steering knuckle ( Thats where the brake hardware bolt to ) must either be loosened at the strut mount or at the lower ball joint to allow the shaft to slip out of the hub assembly. You choose which one is easier.
4.The inner or inboard joint will be held into the transmission by either bolts or by a retaing clip called a circlip. ( Refer the the illustration above)
5. If you see no bolts then you will have to pry the half shaft out the transmission due to the cir clip holding it in there. Be careful not to damage the transmission while doing this. Try using a slide hammer with a CV joint puller attached ot the other end. It works pretty good.
6. Install the new shaft in the reverse. Grease the splines ( Grooves on the shaft with the large nut ) and lubricate the seal in the transmission first. I would replace the seal if you are this far into it, its easier with the shaft out.
7. Use new hardware like cotter pins and axle nuts. Torque the axle nut to spec with the vehicle on the ground. You can find the Torque Spec to the axle nut or CV joint bolts in any Haynes or Chilton Manual .
If you don’t have a manual you can log onto www. alldata.com and for a subscription fee you can have all of your vehicles info for one year.
Well that’s about it. I hope this has answered a few questions for you on CV Half Shaft and hopefully taken the mystery out of how they work. If you like this article then please send it to a friend and let them know about us or if you have a question, then please leave me a comment by clicking on the contact tab at the top of the page.
Until next time, this is Jeff Williams saying ” Thanks for stopping by ” and if this article has been helpful to you then please click on the coffee cup icon and help keep this site running. Thanks. Jeff
