Harry Gibson on January 23, 2023 No Comments
Have you started experiencing any weird symptoms in your car like the check engine light, decrease in fuel economy, and black smoke from the exhaust and you diagnosed a P0108 code? Well, if that is the case, then you are in the right place because, in this article, there will be a lot to cover on this problem.
- Car Diagnostics
- MAP Sensor
- Location
- Trouble Codes
- The Problem
- Causes
- Symptoms
- Diagnosis
- Cost
- Conclusion
- FAQs
Doing your own research before you go out there and spend a ton of money on professional repairs is the way to go. Especially if you are one of those people like me who want to wrench on their cars and solve their own problems. Like in this case with this trouble code.
And misdiagnosing is a really common occurrence when it comes to self-proclaimed car experts. So, if you want to tackle your own problems, then this is the right article for you. First, we are going to learn more about what is car diagnostics and see more about the main tools that you need for this job.
Then we will cover the MAP sensor, its purpose, as well as the codes that are a common occurrence for this sensor. Including the P0108 code and its definition. Once we clear that out of our way, we will move on to the causes, symptoms, and how to troubleshoot this car sensor with a multimeter. So, if you want to learn more, follow along.
Car Diagnostics
Now before we start discussing more about the P0108 code, let’s take a look to learn something more about car diagnostics. People are having similar issues and are not quite familiar with the process of diagnosing a modern car. So, we feel the need to further elaborate on the topic and learn what is this process and how it is performed.
As you probably know, back in the day, things were a lot simpler. Engines were very simple to diagnose and fix. An experienced mechanic could track the problem only by hearing how the car sounds. But those days are long gone.
Cars became a lot more complex in the last 30 years. And also more reliable in the process. Back in the day, an engine didn’t last for more than 150,000 miles, and now you have engines running strong at 250,000 miles. And not to forget the improved fuel efficiency of these modern engines.
And modern engines require modern diagnostics. Since there are a lot of sensors, it means that there is a computer. And access to this computer was standardized in 1996 with the OBD2 port.
Every modern car has an OBD2 port somewhere. And you plug in a special OBD2 scanner tool in order to scan the car for problems. Like in this case with the P0108 code.
And once you have scanned, you can move on to solve the problem. And you can only do this with a special tool known as a multimeter. This multimeter gives you the ability to measure the resistance, voltage, continuity, and other properties of a certain sensor or electrical circuit.
And when it comes to the P0108 code, these tools are essential. Now let’s move on to the next topic.
MAP Sensor
Now before we learn more about the definition of the P0108 code, let’s take a look at the MAP sensor, and what does a MAP sensor do. Later on, we are going to see more about why this is important to know.
So, what is the MAP sensor? A MAP sensor is the Manifold Absolute Pressure Sensor. And the name is really self-intuitive. This sensor is also known as a baro sensor since it is measuring the barometric pressure inside the intake manifold.
This is a sensor that pre-dated the MAF sensor that is used on modern cars. They both do the same job. One is measuring the air pressure inside of the intake manifold, while the other is the amount of air that is sucked into the intake manifold.
And they both help the computer adjust the air-to-fuel ratio in order to deliver excellent performance by attaining the most optimal, best air-fuel ratio.
Although greatly replaced nowadays, this MAP sensor is still used on older cars, and cars with turbocharged engines including both diesel and gasoline. So, we can say that its usage is pretty limited to these applications.
So, we can conclude that this sensor basically helps the computer to adjust the air-to-fuel ratio in the internal combustion process. And when it starts to malfunction, it could trigger codes, like the P0108 code. But more on that, we will cover in a moment.
Baro Sensor Location
Now let’s take a look at the baro sensor location, in other words, the MAP sensor location before we dive into the P0108 code. Where is this sensor located?
Well, since this is an intake manifold sensor, it is expected to be mounted on the intake manifold itself. And this is the case in most situations. So, if you are searching for a MAP sensor, always look at the top of the engine and you will eventually find it. Even though, sometimes the sensor can be mounted on the firewall.
What is worth noting about this sensor is that it is not located on the intake hose like the MAF sensor. So, don’t look there, if you find a MAF sensor, this is the case because the car is running only a MAF, or the vehicle is a turbocharged model that uses both of these sensors.
If your car is instead facing MAF sensor issues, do check out our guide on the replacement cost of a mass air flow sensor. We’ve also discussed MAF sensor-related OBD codes, such as P0102, and P1101, as well as the P0101 Chevy Silverado problems.
Now let’s move on to the MAP sensor codes, including the P0108 code.
MAP Sensor Codes
Now let’s take a look at the MAP Sensor codes including the P0108 and see more about what they mean.
- P0068 – MAF/MAP – Throttle Position Correlation
- P0069 – Manifold Absolute Pressure – Barometric Pressure Correlation
- P0105 – Circuit Malfunction In MAP Sensor
- P0106 – MAP Sensor Circuit Range/Performance Problem
- P0107 – Manifold Absolute Pressure Barometric Pressure Circuit Low Input
- P0108 – MAP Sensor High Input
- P0109 – MAP Sensor Circuit Intermittent
- P1106 – MAP/BARO Circuit Range/Performance Problem
- P1107 – Barometric Pressure Sensor Low Circuit Voltage.
Overall, these are the codes that you will come across when you deal with the MAP sensor on your car. Now let’s move on to the P0108 code and learn more about the definition of this specific code.
Manifold Absolute Pressure Barometric Pressure Circuit High Input
Now let’s learn more about the definition of the P0108 code and see more about what this code is all about.
The simple definition of the P0108 code is “Manifold Absolute Pressure Barometric Pressure Circuit High Input”. But what does this mean?
Well, this means that you have a problem. Specifically, the PCM (powertrain control module) which is the car computer has conducted various tests on the MAP sensor and determined that the voltage that it produces is too high.
Usually, the voltage depends on the throttle. It ranges from one to 5 volts. The more open the throttle, the higher the voltage the sensor sends to the PCM. And in this case, the sensor is registering that your car is working on fully open throttle. Which in reality is not the case.
So, you cannot run your car on full throttle all the time and get 5v or greater readings nonstop. It must be something with the sensor or other components around it. And more on the causes, we are going to further elaborate in the following chapters, where we are going to list all the common causes for this problem with the P0108 code.
P0108 Code Causes
So, we learned what the P0108 code is and its definition. Now let’s move on and learn more about the causes that can trigger a code like this.
And honestly, there could be multiple causes for this problem. And each one of them is worth your attention because you never know, in some cases, the sensor can be actually good and something else could trigger this situation. So, let’s cover the most common causes of the problem.
P0108 Causes #1: Bad MAP Sensor
The first and most common reason for the P0108 code is simply a bad MAP sensor. As with every other electronic component, the MAP sensor can also fail at some point and malfunction on the inside.
Even though this can be the first assumption, you should be jumping immediately to conclusions and replacing the sensor. Mainly because the P0108 code can be also triggered by other issues happening in the wiring harness, as well as the engine.
P0108 Causes #2: Vacuum Leak
The second most common cause for the P0108 code is a vacuum leak. So, what is a vacuum leak? Well, this is a situation when you have air leaking from the intake manifold.
Gases can also leak and cause problems, even though we cannot see them with the naked eye in some cases. There is a vacuum supply line to the MAP sensor that can leak, as well as the intake manifold can leak as well. Otherwise, you’ll need to consider the repair cost of a vacuum leak.
So, you definitely need to check for vacuum leaks before you jump to a conclusions too quickly when it comes to the P0108 code.
P0108 Causes #3: Short On The Signal Wire To The PCM
The next set of causes for the P0108 code that we are going to cover refers to the short in the system. This is when two wires come in contact and short out. This could be caused by rust development on the wire, as well as by corroded wire protection.
So, there could be a short on the signal wire that goes to the PCM. This signal wire is basically the output that the sensor delivers to the PCM. And if this wire has shorted out, it could have a high voltage instead of an accurate reading.
P0108 Causes #4: Short On Reference Wire From PCM
The second most common problem when it comes to the wires shorting out and triggering the P0108 code is the situation when you have a short on the reference 5v wire that goes from the PCM to the sensor itself.
Each sensor is powered by a 5v supply line, which is this wire, a ground wire in some cases, and the 5v signal wire that returns the signal in the form of voltage. So, be really aware of this problem as well, since it can trigger the P0108 code.
P0108 Causes #5: Bad Ground Connection To The MAP Sensor
The next common cause for the P0108 code is a problem with the ground connection. You can have an open ground to the MAP sensor and this could easily trigger a code like this.
Remember that these are three wire sensors that have one ground wire, and you should always have a ground connection in order for these sensors to work as they should. Check the connector and make sure that a proper ground connection is present.
Later on, we are going to learn how you can test the MAP sensor. Now let’s cover the last common cause for the P0108 code.
P0108 Causes #6: Low Compression In Engine Can Trigger
Last on our list of triggers for the P0108 code is the low compression inside the engine. The engine can be really worn out and cause the sensor to malfunction and cause a low vacuum inside. Therefore, it’s crucial that you’re on the lookout for the symptoms of low compression.
This is less likely but it can happen in some cases if there is too much blowby and the car has an oil-burning issue. And honestly, this is one of the last things to check. The leaks on the intake are the most common ones to trigger codes with the MAP sensor like the P0108 code. Now let’s move on to the symptoms.
P0108 Code Symptoms
Now that we covered the P0108 code definition and the causes for this code to be triggered, now we can move on and discuss the symptoms of a bad MAP sensor that will be present whenever this code is on.
Knowing the symptoms is also useful to determine whether you have this issue or not. So, let’s cover the symptoms before we cover how you can test a MAP sensor with a multimeter and how to tackle this problem in no time.
1. Check Engine Light
Now let’s begin with the symptoms of the P0108 code, and the first symptom that you will get is probably the check engine light. Since if you didn’t get the check engine light, you wouldn’t be here.
So, the code P0108 is an outcome of this check engine light in this case. And when this problem happens, there could be some other codes as well. Like a P0171 code which indicates a lean condition.
There could be also other codes from the ones that we listed in one of the previous chapters that are associated with the MAP sensor. Or any other DTC code, this is why you should erase all the codes first and pay the most attention to those that stick. Now let’s move on to the next symptom.
2. Poor Engine Work
The next symptom in our list of symptoms associated with the P0108 code is poor engine work. The engine will run really weirdly in these situations when this sensor does not work well.
You can have rough engine work, rough idle, engine misfires, and whatnot. The engine will not be happy at all in these situations. So, beware of these problems that can be quite common.
3. Engine Not Able To Start
The next common symptom associated with a P0108 code and the situation with the MAP sensor is the situation when the car is not able to start at all.
And this could happen in some cases when the sensor records high voltage all of the time. The car could start and stall immediately and in some cases, it could be difficult to keep the engine running as it should.
So, whenever a problem like this occurs, you know that you have a bad MAP or MAF sensor issue depending on which sensor your car is using.
4. Poor Fuel Economy
The next symptom on our list of symptoms associated with the P0108 code is poor fuel economy. So, why is this the case?
Well, this is the case because your car will not be able to adjust the air-to-fuel ratio if your MAP sensor is not working as it should.
It will record full throttle and the car will think that it should dump enough fuel for the highest RPM. So, the injectors will blast the cylinder with the maximum fuel possible and this consequentially will reduce your fuel economy to the minimum. And our next symptom is also associated with poor fuel economy.
5. Black Smoke From The Exhaust
As we noted previously, the computer will dump quite a bit more fuel than needed when the MAP sensor malfunctions, so you will have bad fuel economy if you have the code P0108.
But you will also have black smoke or the smell of gas in the car or coming from the exhaust pipe. This would be the case because there is a lot of fuel and this fuel will be unable to burn completely.
And on top of that, you will also damage the spark plugs, O2 sensor, and catalytic converter if you run your car like this for a long. But how to test the MAP sensor and fix the problem? More on that, we will discuss it next.
Test Map Sensor Multimeter
Now let’s see how you can test this sensor on your car. As we noted, this is the case when the sensor reports high voltage. So, if you have a code scanner with advanced functions you can access the live data and see the readings while the engine is running.
If you don’t have this type of OBD2 tool, you can always test the sensor with the good old multimeter. Multimeters are really cheap and inexpensive tools that are lifesavers in these situations.
You can test this sensor by backprobing it. Get two wires and place them in the connector from the backside. Then tweak the multimeter to volts and start the engine. Then you will have live data of the voltage.
And in this case, if the sensor is bad, it should read somewhere close to 5 volts. If this is the case, then the sensor is probably bad. More about the testing you can check in the video above.
Also, make sure that the vacuum hose that goes to the sensor does not have a leak because this could trigger the P0108 code as well.
Cost To Replace MAP Sensor
The cost for a MAP sensor is anywhere between $70 and $250. It really depends on the make and model that you have. Some models have more expensive components. Some of them are rather cheap.
P0108: In Conclusion…
In this article, we have covered quite a bit when it comes to the P0108 code. First, we learned about car diagnostics and MAP sensors in general. Then we covered the P0108 code definition.
Once we cleared that out of our way, we learned the causes, and symptoms, as well as how you can test a MAP sensor with a multimeter. Lastly, we covered the cost involved in replacing it.
Frequently Asked Questions
Now let’s answer some frequently asked questions.
How Does A MAP Sensor Work
A MAP sensor is a rather simple device. This sensor measures the barometric pressure inside the intake manifold and helps the engine to adjust the air-to-fuel ratio. Back in the day, every car had one, nowadays only turbocharged applications use MAP sensors.
How To Fix MAP Sensor
You can try cleaning the connections, as well as cleaning the sensor with compressed air. But we doubt that anything will help if the sensor has malfunctioned inside. The best is to replace it with a new sensor.
Can I Drive With A Bad MAP Sensor
You can drive with a bad MAP. But it is only a question of time before the symptoms will get worse and the car not be able to start eventually. And also, by running the car like this you can damage other important components.
How To Test MAP Sensor With Multimeter
You can backprobe the sensor, and place iron clips in the 5v supply and the 5v reference wire connectors from the back. Then tweak the multimeter to measure volts and start the car. When the car starts, the voltage should be 0.9 volts. Then as you give the gas, it should rise to a maximum of 5v. If this is not the case, then you have a bad sensor.
Will A Bad MAP Sensor Throw A Code
Yes, it will definitely throw a code. Some of the more common codes are P0068, P0069, P0105, P0106, P0107, P0108, P0109, P0105, P1106, and P01107.
What Causes A P0108 Code
Most often, this code is triggered by a bad MAP sensor. But in some cases, this can be due to a vacuum leak from the hose that goes to the sensor. Also, the problem can be triggered by problems with shorts in the electric circuit of the sensor as well as on the wiring of the sensor.
