BAD THROTTLE POSITION SENSOR? HERE'S HOW TO SPOT PROBLEMS AND REPAIR THEM

There are so many different parts that are found in your car. Most of them work just fine and require no attention from the driver - until they go bad, that is. Your throttle position sensor is one of these little-known but important components.

When you have a bad throttle position sensor, you will know it right away, and you will have to deal with it without delay. Join us for an insider's view of what a throttle position sensor is, what it does, what makes your throttle position sensor go bad, how to know if it goes bad, how to clean or replace your throttle position sensor, what replacing it costs, and finally, whether it is worth fixing a bad throttle position sensor.

What is the throttle position sensor and how does it work?

In today's engines, with their strict emission controls, computers are in charge of virtually all aspects of the combustion process. Each car's engine computer must precisely control the metering of the fuel and air according to the driver's demands. It should provide the power that the driver needs, while maintaining good fuel economy and low tailpipe emissions.

The throttle position sensor is an electronic device that monitors the position of the throttle, which directly relates to how far down you have pushed your gas pedal. This regulates the amount of air entering the engine, which much then be matched by an appropriate computer-provided amount of fuel to mix with the air. The fuel-air combination will then enter the cylinders, where it is compressed, ignited, and burned to produce power for your vehicle.

By observing the electronic signals coming from your throttle position sensor, along with the information from other engine sensors, your engine computer can send the right amount of fuel to go with that air, so that your engine will produce the exact amount of power you are requesting from it. When everything is working correctly, your engine responds smoothly and instantly to your right foot's commands.

But when you have a bad throttle position sensor, the engine computer is no longer getting the right information, and may be unable to correctly interpret what you want the engine to do. Depending on the exact nature of your bad throttle position sensor problem, your car could be very difficult to drive, it could get stuck on the side of the road, or it could even accelerate uncontrollably - a very scary and dangerous situation!

What problems will a bad throttle position sensor cause?

While your throttle position sensor will normally last the life of the vehicle, there are exceptions. Your throttle position sensor is a component with both electronic and mechanical parts, so it is subject to damage and wear to both subsystems. In addition, your throttle position sensor lives in a very hostile environment, under the hood and on your engine. This subjects your throttle position sensor to heat, hot fluids, jolts from potholes, and other hazards of its "neighborhood." Here are some of the causes of a bad throttle position sensor -you will often see more than one of these appearing at the same time, making the diagnosis easier:

Acceleration and power delivery issues

This can cover a wide variety of different symptoms, all related to your not getting the response you wanted when pushing down the gas pedal. It's all because a bad throttle position sensor is sending garbled messages to the engine computer. You may experience:

• • • Poor acceleration
    • Surging acceleration
    • Hesitation
    • Sudden acceleration when you are not pushing the gas pedal
    • Inability to travel at higher speeds
    • Bucking and jerking
    • A delay from when you step on the gas until the car responds
    • Engine misfiring

Idling and stalling problems

This is the low-engine-speed version of the issues created by a bad throttle position sensor. Just as with the acceleration problems above, your bad throttle position sensor is unable to send the correct airflow information to the engine computer, so it is unable to provide the right amount of fuel for proper running. You may observe these symptoms:

• • • Rough idling
    • Slow, unstable idling
    • Surging idle
    • Stalling right after starting
    • Stalling while driving
    • Stalling under hard braking

Failure to start

This is exactly what it sounds like - your car won't start, due to a bad throttle position sensor. It may crank but not catch, it may die right after it starts, or it may not even crank. Time for a tow.

Excess fuel consumption

A major drop in fuel economy is a direct byproduct of the abnormal engine behavior that results from a bad throttle position sensor. All of that surging, misfiring, and sudden acceleration waste fuel. On top of that, the false readings sent from your bad throttle position sensor to the engine computer force it to compensate in ways that are not energy efficient. This symptom is unlikely to appear by itself, but it will confirm the diagnosis of a bad throttle position sensor, when added to the other, more obvious signs as noted above.

Check Engine Light comes on

Because your bad throttle position sensor is considered part of your car's emission control system, its malfunction is likely to illuminate your Check Engine Light (CEL). The CEL might flash, or it may remain illuminated. A code scanner can be attached to your car, and the trouble code retrieved. This will help to diagnose whether you have a bad throttle position sensor.

Difficulty changing gears

The acceleration problems that are the result of a bad throttle position sensor can also affect the way that your transmission shifts (or doesn't). The incorrect electronic signals being sent by your bad throttle position sensor are also used by your automatic transmission's computer, to help it decide when and how to shift. Both upshifts and downshifts can be rough, delayed, or even made at random, making driving even more difficult.

Limp-home mode is activated

Many current vehicles have engine computers that are sophisticated enough to recognize a serious condition like the one caused by a bad throttle position sensor. To protect the engine, transmission, and the entire drivetrain from possible damage, it will enter what is known as "limp-home" mode.

This is the engine computer's back-up setting, which is tripped when a major sensor like the throttle position sensor fails. Engine power is restricted, and the transmission is locked into a single gear, usually second or third. The CEL will also come on, to notify you of the problem. You will be able to drive at a maximum of around 45 mph - directly to a repair shop! Once your car is fixed, the mechanic can reset the computer and the CEL to normal operation.

How to test the throttle position sensor

Testing your throttle position sensor requires some serious in-depth knowledge and experience in diagnosing automotive electrical systems and electronics. Unless this sounds like you, this job is not for the average DIYer. A professional repair shop with the right tools, equipment, and personnel to track down the problem with your bad throttle position sensor is where you should be headed. Here's the short version:

First, use an OBD-II code reader to retrieve the trouble codes from the engine computer, with the engine off. Make a note of these codes. Next, clear the codes, then start the car to see whether the codes come back. If they don't, you may have a problem that is intermittent in nature. If the codes do return, and pertain to the throttle position sensor, you definitely have an issue.

The next step is to do a visual inspection of all the throttle position sensor wiring, including all connectors. Check that everything is in good condition, intact, and properly connected. Fix any wiring issues.

Now for the tests of the electrical system:

1. Using a digital multimeter (DMM), check for continuity between the sensor terminals. Any open circuits mean you have a bad throttle position sensor.
2. Find the value for your throttle position sensor's internal electrical resistance by checking the manufacturer's product information. Use the DMM to verify that this is correct between the two terminals that are farthest apart. If it is not, you have a bad throttle position sensor.
3. Test the reference voltage; if it is too low or nonexistent, you may have a wiring problem.
4. Test the ground if you got a good reference voltage; if the value is low, you may have a poor ground.
5. Switch to an analog multimeter and watch the needle as you move the throttle flap; if the needle stops while flap is moving, or it goes in a counter-clockwise direction, you have a bad throttle position sensor.

There are additional tests that can be run with a diagnostic scanner, or a scan tool that can display live data.

How to adjust the throttle position sensor

While many types of throttle position sensor are not adjustable, there are some that can be adjusted. The first thing you should do is to access the manufacturer's repair-related information for your vehicle's throttle position sensor, to determine whether your throttle position sensor is indeed adjustable. You will also need the correct specifications for a properly adjusted throttle position sensor.

Once you have done this, and you know that your throttle position sensor is adjustable, you can begin the process. Make sure that your battery is fully charged, and that your throttle cable and throttle stop are properly adjusted.

Using a voltmeter, multimeter, or ohmmeter (whichever is specified), attach one lead to the ground, and the other to the sensor signal wire. Start the engine and let it idle, then loosen the screws that hold the throttle position sensor in place. Rotating the sensor, watch the meter for the proper voltage listed in the manufacturer's specifications. When you see the correct reading appear on the meter, tighten the screws. You are done.

How to clean the throttle position sensor

If you suspect that you have a bad throttle position sensor, and you feel confident in your ability to access it on your car, then it might be worth cleaning your throttle position sensor. This could be an inexpensive way to solve the problem, before taking the vehicle in to your local mechanic or repair shop. Why? Because if the sensor is dirty, it can transmit incorrect information to the engine computer, producing similar symptoms to a bad throttle position sensor. Here's how to clean your throttle position sensor:

• • Go to your local hardware or auto supply store. Purchase a container of throttle body cleaner. You will also need a screwdriver set, standard and socket wrench sets, and a few microfiber towels.

• • Move your car to level ground and start it up. Let the engine warm up a bit, as this will make the throttle position sensor easier to clean, by softening any dirt and grime.

• • Next, open the hood and access the sensor. If you have a vehicle where too much disassembly is needed to reach the throttle position sensor, you might prefer to leave this job to a professional mechanic. If your throttle position sensor is easily accessible, find it. (take a picture with your phone that shows how the throttle position sensor is installed, to make it easier to reassemble after you're done cleaning it.)

• • Disconnect the wires connecting the throttle position sensor to the vehicle. Clean the throttle position sensor with the throttle body cleaner and your towel. Don't use too much cleaner, just enough to get the throttle position sensor clean. Be sure to also remove any dirt or grime on or around the throttle position sensor. Finally, be sure that any of the liquid you used for the cleaning process has dried completely or has been wiped away with a clean dry towel.

• • Reinstall and reconnect the cleaned throttle position sensor accurately and securely, leaving things as you initially found them.

• • Start your car and check whether the cleaning solved the problems with your throttle position sensor. If not, the next step is a replacement for your bad throttle position sensor.

How to replace the throttle position sensor

If cleaning your throttle position sensor did not result in any improvement to your car's running condition, it is probably time to consider replacing your bad throttle position sensor. Just as with the cleaning process, if your throttle position sensor is difficult to access, or you are otherwise not up to tackling this procedure, take your car to a repair shop. If you feel confident in attempting it, here's how:

1. Purchase the correct replacement throttle position sensor, either at an auto parts store or online.
2. Shut off your vehicle and disconnect the battery.
3. Open the hood and access your bad throttle position sensor. Disconnect the electrical connector, unfasten any mounting hardware, and remove the bad throttle position sensor.
4. Install the new throttle position sensor.
5. Reconnect the electrical connector.
6. Reconnect the car's battery.
7. Adjust the new throttle position sensor if required (see the original manufacturer's information and the section on this above).
8. Turn the key on, but do not start the engine. Using a scan tool, clear the codes stored in the engine computer's memory.
9. Take your car for at least a ten-minute drive. Accelerate normally and see if the car performs as it should.

How much does it cost to replace the throttle position sensor?

The answer to this question needs to be broken down into two parts:

1. What does the throttle position sensor for your car cost?
2. How much work is required to get to your throttle position sensor?

Throttle position sensor cost - and quality

There is a range of answers to the first question, based on whether you get an original equipment (OE) replacement part (sold under the manufacturer's brand and made to its standards) or a cheaper aftermarket part. The OE part will meet the carmaker's performance standards and should perform the same as one in a new car. The aftermarket part may or may not perform to these standards.

Depending on the year, make, and model of your vehicle, the OE replacement throttle position sensor can run anywhere from a few hundred dollars and up, while some versions of the cheaper aftermarket part might start under $100. Keep in mind that OE parts usually come with warranties, and they should work very well. The aftermarket parts may not be made for your specific vehicle, but may instead be a consolidated specification part, made to work adequately on a variety of different vehicles. How well it works on your car will be revealed when you install it.

This may be one of the few times when you are better off paying more for the OE part.

Labor costs: Getting to the throttle position sensor

The next part of the cost equation relates directly to how much labor is required to get to the throttle position sensor. Some vehicles place them in an easily accessible condition. Others bury the throttle position sensor deep inside the engine, behind plastic trim covers, air filter boxes, and intake manifolds. This can add up to some hefty labor charges, which can easily be several hundred dollars.

It could be cheap, or very expensive

Due to all these variables, there can be a very wide range of costs for the total job. Using a cheap part, along with having a car that lets you easily access your throttle position sensor so you can do it yourself, might only cost you a hundred dollars or so. Using a more expensive OE part, with a complex car that requires a ton of mechanic's labor to get to the throttle position sensor and replace it, and you could be facing a $1000.00 bill for parts and labor. Ouch!

If you aren't planning to do it yourself, the best course of action is to call several well-rated repair shops. Get some firm estimates of repair costs for the throttle position sensor that fits your specific vehicle.

Can you drive with a bad throttle position sensor?

This is not one of those car problems that you can ignore. If you have a bad throttle position sensor, your car will not perform well or safely. Driving with a bad throttle position sensor may also cause problems in other related systems in your car, which will mean additional repair bills.

In addition, any trouble codes that your bad throttle position sensor caused to be sent to your engine computer will need to be resolved and cleared. Otherwise, you will not be able to pass a smog inspection if needed, and you will have difficulty in selling your car to a dealer or an individual. Instead of driving with a bad throttle position sensor, you should have it fixed immediately.

Is it worth fixing your throttle position sensor?

If you do need your throttle position sensor replaced, and your car is otherwise in good running condition, it is definitely worth fixing. First and foremost, this is because you can't drive your car safely if the throttle position sensor doesn't work! The consequences of not being able to accelerate, exactly when you need to (like hesitation during a left turn, for example), can put you in a very hazardous situation!

On the other hand, if your car is very old, has a lot of miles on it, is not particularly reliable, and the cost of fixing your throttle position sensor is high, you have a decision to make. Here are some questions to ask yourself:

• • What is your car worth?

• • How many miles are on it?

• • Does your car have any other chronic issues that could result in a big repair soon?

• • Will the brakes or tires need replacement soon?

• • Is it time to cut your losses and get rid of your car now?

We buy junk cars with mechanical problems.