Trouble Code P0108: MAP Pressure Circuit High Input
Trouble code P0108 is a generic code that is caused by your manifold absolute pressure, or MAP, sensor. How do I fix trouble code P0108? Learn more about this circuit issue, common symptoms and how to diagnose and resolve typical issues with most makes and models of vehicle.
What Does P0108 Mean?
Your engine vacuum is measured by your MAP sensor. A higher vacuum results in a lower reading from your sensor. It helps your powertrain control module determine whether your engine is at idle, full throttle or anywhere in between.
A MAP sensor includes three wires. One is used to create a voltage reading based on the negative air pressure. Another is a five-volt wire used as reference connecting the powertrain control module and MAP sensor. The last is a ground wire.
A signal of one volt means that your engine is at idle and has a high engine vacuum. A five-volt signal is the result of a wide-open throttle and little or no negative air pressure. Under normal operation, your MAP sensor shouldn’t receive any signal over five volts. When it receives a signal over five volts, or a high signal when the powertrain control module otherwise believes your engine is idling, it will trigger P0108 trouble code.
Common Symptoms
Now that you know what typically causes P0108, what does the code P0108 mean? Depending on the cause, there’s a few common symptoms that come with this DTC code:
- Black exhaust smoke
- Failure to start your engine
- Poor running performance
- Decreased fuel economy
- Malfunction indicator lamp illumination
- Error code P0108
Typical Causes
If your engine is operating normally, your error code may be the result of a damaged MAP sensor. A short in the sensor could cause a signal of five volts even when your vehicle is idling. This is not only the easiest fix, it could mean that there aren’t any issues with your engine.
All three wires leading to your MAP sensor could also be frayed, loose or damaged. An electrical short will trigger P0108, so it’s a good idea to inspect your wire harness to ensure there’s no visible damage.
Less common, but more serious, your engine could have a vacuum leak or other damage. A worn-out engine may not have the same vacuum as a brand-new one, and this inefficiency could be extreme enough to alert your MAP sensor.
Solutions and Repair Procedures
One way to determine whether your MAP sensor is working correctly is to compare it with a Barometric pressure reading. When you have your key on and engine off, check the MAP sensor reading. It should be the same as your Barometric pressure reading. A difference of more than 0.5 volts is a sign that you need to replace your MAP sensor.
Inspect your wiring harness for any signs of burnt, broken, crushed or frayed wires. Loose connectors, moisture buildup in the wire harness and frayed wires are all common issues that could cause error code P0108.
Finally, if your sensor is working properly, there may be a vacuum leak in your engine. Check the vacuum hoses and connectors to ensure a proper seal. You may need to turn your engine on and use a scan tool to determine whether your engine is properly sealed. A reading of less than 15 in. Hg means that your engine needs a stronger vacuum in order to operate efficiently. After you’ve checked all these signs of a OBD-II scanner error code P0108 problem, clear the code and test your voltage again to see if your MAP sensor is working properly. Inspect related issues, such as error codes P0105, P0106, P0107 or P0109 to help identify the exact issue.
