Glenn Stok uses his design background come solve technological problems and also save money on automobile repairs. He share his insight below.

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If your "check engine light" is on and your mechanic claims you require some high-quality repair, there is an easy way for friend to inspect if he is informing the truth. You have the right to read her car's diagnostic trouble codes yourself through a low-cost Diagnostic password Scanner that plugs in under the dash to accessibility the car’s computer.

This article will present you just how to know what your examine engine light means, whether over there is a real difficulty or simply a faulty sensor, just how to reset the light, and potentially stop expensive car repair bills.There are countless component fail that rotate on the inspect engine light. Among the many expensive to fix is the catalytic converter. However, many times the light is motivated by nothing much more than a faulty sensor.

Here's what you'll get from this article:

I'm walk to explain how to read your car’s diagnostic codes.I will also explain just how to phone call whether there is a real concern with her engine, or merely a faulty sensor that triggered the light.I'll display you exactly how to clean the irradiate so the you can pass one inspection.Some cars additionally have a "Check tires Pressure" light. I'll discuss that too.Finally, ns conclude with a section listing usual questions readers have been asking, together with my answers.

Understanding your Car's Diagnostic Codes

Your car's computer, known as the Powertrain manage Module (PCM), keeps a record of the diagnostic codes that stand for which sensor is reporting a problem.

The check engine light come on when any type of sensor reports a faulty device. However, it may not be the device that is bad. It may simply be an cheap faulty sensor.

When sensors fail, that is usually intermittent. A valuable experiment is to clear the codes and also watch to watch if the check engine irradiate comes ago on. You can read her car’s diagnostic codes with a an easy code scanner. The plugs right into a distinct plug the you can find under the dash.

You can also use these scanners to reset the PCM by clearing any type of saved trouble codes.

Since I have a background in computer science, i am conscious that the only way the PCM will know if a unit is failing is by a sensor reporting back to it.

When a password is stored, the inspect engine irradiate is lit to let friend know. A certain diagnostic code shows which sensor report the problem. This codes are recognized as the OBD-I and OBD-II codes, but an ext on that in a moment.

Sensors have the right to Fail and also Report False Codes

Your car has sensors for many components. Most are regarded emissions manage (see listed below for much more about the tire press warning light on newer cars).

Sometimes a sensor will certainly fail or obtain stuck and also report a false code. An moral mechanic will tell girlfriend that. Instead of a sensor is no that expensive.

You can do your very own cheap engine diagnostics through using among these low-cost password scanners. That will help you discover why your inspect engine light is on. Yet knowing if it's a sensor problem takes some extra work, together I'll explain.

Choosing a Diagnostic code Scanner

Many time I have actually noticed the mechanic plugging in a code scanner under the dash to check out the engine trouble codes indigenous the car's computer. Ns thought exactly how nice it would certainly be to recognize why the examine engine irradiate is on before I go into the fix shop. So I made decision to spend a tiny money top top my an extremely own Diagnostic code Scanner.I walk a few searches because that these units and found reasonable prices and also a wide an option of models on Amazon. Prices selection from approximately $50 come the upper $200's depending on the model and also features. After a tiny review, i realized that ns didn't should buy the most expensive one.If you have actually a 1996 or newer car, climate the cheaper models that Diagnostic code Scanners will certainly do simply fine. Every vehicles since 1996 use the OBD-II codes. The more expensive code Scanners can read the larger OBD-I codes together well. The is not essential to have unless you have actually an older car built before 1996.

Why It's Worth gaining an OBD code Scanner

Replacing the catalytic converter have the right to be expensive for parts and labor combined. If you have actually your annual State Inspection coming up, then you will certainly be required to pay for the repair to pass the inspection.The catalytic converter is component of the auto exhaust system, placed in between the engine and also the muffler. The reduces the toxicity the emissions indigenous internal combustion engines.It was an initial introduced in the U.S. In the mid-1970s to comply v EPA regulation for managing auto exhaust. Its features are monitored this particular day by the car's computer system system with sensors that space on all important auto parts.The sensor that detects a problem with the catalytic converter is known to expedition erroneously sometimes. It happened to me and also to numerous friends. I never required a replacement because it was simply a tripped sensor resulting in the examine engine irradiate to come on.The catalytic converter commonly has a warranty exceeding the remainder of the automobile's warranty length. However, if friend are past that warranty period (by time or through mileage), climate you could be dealing with a large repair bill.

If you're in a state the implements auto emission inspection programs, girlfriend might likewise get stuck to needing that repaired quickly due to the fact that your vehicle failed.You may have the ability to avoid instead of the catalytic converter. In plenty of cases, it's just a bad sensor, and you wouldn't understand that uneven you have the right to clear the car's diagnostic codes and also watch to view if the inspect engine irradiate comes ago on.

How to review Your code Scanner

This scanner the I usage doesn't call for me to look up the an interpretation of the codes. It shows the summary of the codes on the screen. It also lets you reset the inspect engine light by clearing the password from the computer.Most diagnostic scanners offer comparable features. Actron has versions that also read OBD-I codes in enlarge vehicles through an optional cable. By reading the password myself, i was may be to see that my difficulty was without doubt the catalytic converter.

Each code scanner is different, however they all present you the standard difficulty codes and also have a function that allows clearing and also resetting the computer. I recommend the you check out the user's manual. Most an excellent scanners will overview you with the procedure on the little screen if you closely follow along with the on-screen prompts.

How to Tell If girlfriend Really have actually an Engine Problem

There is no method to understand right far if the light is on due to a faulty sensor. You should erase the code and then see if that comes earlier on eventually.

My scanner offered me all the functions I needed to check out the codes and erase them. I very first chose the alternative to scan for any type of trouble password in the computer. Mine scanner also shows the an interpretation of the codes in plain English. It's great to know this before erasing the codes. Then I pick the alternative to erase the password from the computer.

But you're not done yet! To know for certain whether the concern is a faulty sensor or a catalytic converter that demands repair, you need to follow a couple of more steps.

Diagnosing the Problem

After friend reset the codes, either of two points will happen.

If the "Not Ready" condition becomes "Ready," and also the check engine light did no come earlier on, climate the problem may have been an intermittent faulty sensor.If the examine engine irradiate does come earlier on, climate the scanner will display you that bad code again. That would indicate you execute indeed have a component fail as mentioned by the code. In the case, at the very least you'll understand you will be spending money to solve a actual problem.

In instance you're wondering whether you go out the irradiate by turning it off, that is certainly not the case. An initial of all, the Diagnostic password Scanner check the condition of the check engine light as well. Secondly, once you revolve on the ignition without starting the engine, all the dashboard lights light up temporarily as a test, for this reason you deserve to see lock all room working.

Passing the yearly State Inspection

You will certainly not happen inspection if the light is no off. That is achieved by clearing the codes from the computer. However to happen inspection, the computer additionally has to display a "ready status." If you were to lug your car in because that an inspection, the mechanic would certainly tell you the he or she can't pass the vehicle at the time.

When you clean the codes through the “Erase Codes” function, the status of the mechanism Monitors is collection to “Not Ready.” You have to drive 50 come 100 miles in number of individual trips until the system reads the status of all the components again.

“Several trips” way that girlfriend shut turn off the engine and start another trip. Therefore it's not simply 100 miles in one trip. It's much more like making 3 trips of about 30 mile each.

Then connect the scanner again and also read the system Status to watch if the "Not Ready" problem is unable to do for all codes the you had cleared.

Three device Status conditions You have to Understand

System condition Explanation


If the examine engine light did no come ago on, the mechanism is working properly and also your vehicle will pass emissions tests.


Your automobile has no been driven enough after resetting the codes. You should drive till the system indicates a ready condition.


This method that your auto does not support that standing monitor and you don't must be concerned around it.

Do you have actually a question?

See "Questions native Readers" in the last section below, together with the answers.

High-End code Scanner With more Features

Some people prefer come spend more money to have actually many an ext features the replicate what have the right to be done by organization mechanics. Ns don't find any kind of need because that this just to monitor our own worries when the inspect engine light come one.

With a an easy scanner favor the persons I mentioned above, you can get a good idea the the problem, and also then bring your car in because that a more precise checkup by a mechanic girlfriend trust.

Nevertheless, if you want a scanner that does a lot more, the INNOVA 3160 may be what you'll want to have. However, I'm satisfied v the one I use (mentioned above), i m sorry is under $50.

Understanding the Tire press Warning Light

In 2008 the nationwide Highway website traffic Safety management introduced a new requirement that all brand-new cars and light van must have a Tire press Monitoring mechanism (TPMS).These more recent cars and trucks have actually a TPMS warning irradiate in the dash, which will come on if the press on any type of of the tires is listed below 25% of the encourage pressure. A flashing or blinking TPMS light way that one of the TPMS sensors is malfunctioning.The TPMS codes room not had in the ODB i or II codes and will no be known by an OBD scanner. A firm named Accutire provides a tire press monitor especially for the objective of analysis the TPMS codes.


This scanner display screens diagnostics results of Sensor ID, tires Pressure, Temperature, Battery Condition, and OE part number. Unlike the an approach of analysis the OBD codes, no physical link is compelled to read the standing of the TPMS. The reads the data via wireless signals.

There are two approaches for the TPMS device to work:

One method is indirect by making use of the ABS/wheel-speed sensors (wheels spin at various speeds based upon their inflation).The other technique is a direct valve sensor.

If your “Tire press Light” is on, examine the press in each tire. The encourage inflation press for most passenger automobile tires is 32 to 34 PSI once cold. Yet check her car's owner's hand-operated for its suitable pressure.

Drive a if after correctly inflating your tires. The will provide the system a chance to it is registered that the push is okay.If the TPMS light does not go off after control a while through the correct inflation, or if it's flashing, it might mean a fault v the tire push sensor, or through some other part of the monitoring system. You will require to find out what error code you have.Some after-market wheel are known to have an issue. The sensor will certainly not fit correctly if the valve feet is in the middle of the wheel’s barrel. If you space buying new wheels, inspect with your dealer to check out if they have wheels that are TPMS-compatible.

Questions native Readers about the check Engine Light

These are common questions people have to be asking, together with my answers.

Does the inspect engine light ultimately turn turn off without addressing the problem?

If the difficulty is not due to an actual component, but rather simply a faulty sensor the is intermittent, climate you may an alert the irradiate goes turn off after part time. Yet it may come back on again when in a while if the sensor continues to send faulty signals.

It's finest to have a mechanic look in ~ it. Yet tell them that it appears to be a faulty sensor, for this reason they recognize you already have some understanding of the situation.

I recognize two friends who paid dearly for a brand-new expensive part, only to have the irradiate come earlier on weeks later. The mechanic refuse to refund the cost, stating the he had no way of understanding it was only a negative sensor. Don't fall for that.

Is the catalytic converter connected to the car's computer?

Yes, that's among the components that is monitored by the Powertrain control Module (PCM), the car's computer. If the Catalyst System efficiency is listed below the threshold then it it is registered error password P0420.

Can the Actron scanner read individual sensors?

Yes, that will read all sensors and also display the results. Climate it allows you optionally clear the password from the computer system to begin fresh.

How countless miles have to be driven to reset examine engine light for inspection?

After you clean the computer, you must drive as much as 100 mile to give it a chance to monitor all the sensors and register the results. Occasionally it might be completed in around 50 miles. You'll know when you affix the scanner and check the status. It speak you if ready or not ready. Wait until you see whatever is in ready status before going for an inspection.

If you clear check engine codes through a scanner, will certainly it permit you to pass inspection?

If the difficulty is a faulty part, the chances are great that the computer system will read a brand-new error and also register a password again by the moment you get into the shop for the inspection. The function of this short article was not to cheat the system but to avoid costly repairs when only a sensor is in ~ fault.

If it's only an intermittent trouble with a sensor, it might take a while because that the sensor to acquire stuck again, and also you will pass inspection. Uneven the sensor is so bad that it it is registered a code again before you get your auto inspected. In any case, remember to wait until the computer system registers "ready," as I pointed out in the critical answer.

If ns reset my light, will certainly it present up in state inspection?

As long as you wait because that the computer to show a "ready status," climate there will certainly be no clue that you reset the computer. However, if you execute indeed have a problem, it will ultimately register the password again and also the light will come ago on. See my former answer about how numerous miles you must drive prior to the ready condition is established.

I gained a new catalytic converter, and also my inspect engine light is still coming earlier on. Why?

When the check engine light comes on, and also the scanner code mirrors that the catalytic converter is the cause, it can merely be the sensor the failed. That's why ns recommend making use of your very own scanner to clear the computer and see if the light comes back on. If the sensor is faulty, it might be intermittent.

When a car mechanic reads the code, they'll most likely sell you an expensive catalytic converter as soon as all you needed was a new sensor. Over there is no means for them to recognize without clearing the computer and waiting to check out what happens.

Is it feasible that it could be a loose gas cap?

A loose gas cap causes a fuel vapor leak sensor come register code number P0455, and also the inspect engine light will come on. But this code may be indicating a more serious problem. You can have damage anywhere in the EVAP system, i beg your pardon captures and also returns the fuel vapor.

So, by all means, make certain your gas cap is tight. And also if it's seal looks damaged, gain a new gas cap. However if the light proceeds to come on and your scanner shows P0455, then obtain it checked out.

QUIZ: test Your understanding of the inspect Engine Light

For each question, choose the ideal answer. The answer key is below.

When go the inspect engine irradiate come on?When the vehicle is thrust too fast.When the vehicle needs an oil change.When a sensor suggests an emissions problem.The catalytic converter is component of...The exhaust system.The electric system.What execute OBD Diagnostic password indicate?How fine the driver is operation the vehicle.They suggest which sensor is detecting a problem.When would certainly a sensor report a faulty code in error?When the computer system gets also hot.When a sensor gets stuck.When the car was no maintained.The diagnostic trouble codes in the car's computer will stay forever.True, they keep a history.False, as soon as cleared and also the part is fixed, over there is no recommendation to the problem.A Diagnostic code Scanner is provided to...Repair the difficulties reported with the OBD codes.Read the codes from the car's computer.Read the password from the defective parts.Can a loose gas cap reason the check engine light to come on?YesNo

Answer Key

When a sensor suggests an emissions problem.The exhaust system.They indicate which sensor is detecting a problem.When a sensor gets stuck.False, as soon as cleared and also the component is fixed, there is no recommendation to the problem.Read the password from the car's computer.Yes

Interpreting her Score

If friend got between 0 and also 2 correct answers: i was hope you'd remember several of this ingredient from the article.

If you got in between 3 and 4 correct answers: ns was hope you'd remember some of this ingredient from the article.

If you got 5 exactly answers: You deserve to do better.

If you acquired 6 correct answers: an extremely good!

If you acquired 7 exactly answers: You're a pro!

This contents is accurate and also true come the best of the author’s knowledge and is not expected to substitute for formal and individualized advice native a default professional.

Questions & Answers

Question: will the examine engine light go off instantly if you adjust the faulty sensor?

Answer: The OBD diagnostic system will reset immediately after a when if the status clears up and also is no much longer detected. That might take as much as over 100 mile of driving.

If you have actually it replaced by a mechanic, lock will commonly reset the condition for you. Friend can always do this yourself with a low-cost diagnostic tool, such together the one I pointed out in this article.

If that is only the sensor that is faulty, the inspect engine light have to not come earlier on. If it was not shut off by the mechanic, it should eventually reset as soon as the OBD device no longer detects a problem.

Question: What execute the OBD password P0300 and also P0339 mean?

Answer: below is the answer:

• The P0300 OBD code suggests “Random Misfire Detected” - This means not every cylinders are firing properly.

• The P0339 OBD code suggests “Crankshaft position Sensor B Circuit Intermittent” - It means that the powertrain regulate module (PCM) is detecting an erratic voltage from sensor B, which is the an additional crankshaft position (CKP) sensor.

In both cases, you need to have your mechanic examine your car to identify if repairs space required.

Note the you can conveniently search because that the an interpretation of any type of code you yourself by putting it into Google along with the keyword “OBD code.” Such together "OBD password P0300" that you asked about.

Question: I'm getting code P0340 on my 2002 Oldsmobile Alero 2.2L, which shows a camshaft position, sensor circuit malfunction. This engine doesn’t have actually a camshaft position sensor. I changed the crankshaft position sensor. I started the vehicle before clearing the code. Will certainly the sensor still present as negative in the PCM? What else must I perform to settle this password so I can pass emissions?

Answer: In enhancement to describe a problem with the Camshaft position Sensor, the P0340 password could also be indicating a problem with the wiring indigenous the sensor come the PCM. That could additionally be a bad PCM together well.

The sensor reads the data that the camshaft gears, for this reason the P0340 password could likewise mean a timing problem. Therefore, you should examine the timing belt. It have the right to be worn or loose.

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Question: What wake up if you clear the codes by taking the battery turn off in your car?

Answer: That's the very same as clearing the codes through the diagnostic scanner. The "Ready status" demands to it is in reestablished prior to your vehicle will happen the emissions test. The "ready status" occurs automatically after steering a reasonable street as described in the related article. The OBD error code will certainly reappear and the examine engine light will certainly come back on if the initial error is detect again.