Richard McCuistian, ASE Certified Master car Technician

Technical Reviewer at

Written by Staff writers - update on august 12th, 2021

When the ECM/PCM detects a problem with the signal sent out by the Manifold Absolute press (MAP) sensor the P0108 code will be stored by the ECM/PCM. Learn more about this password in the complying with guide.

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What does the P0108 password Mean?

Diagnostic trouble code (DTC) P0108 code stands for “Manifold absolute Pressure/Barometric pressure High.” it is motivated by the ECM when it receives a signal from the MAP/BARO sensor circuit that is over the typical range.

Typically, the MAP/BARO sensor is supplied with regulation volts by the ECM top top a 5-volt recommendation circuit. Enlarge Fords use a three-wire sensor that provides 5 volts, but the output signal no a voltage, the a frequency. In ~ sea level through the engine off and the crucial on, a Ford MAP sensor frequently reads about 158 hertz, but when the engine starts, the frequency autumn to about 110 hertz. ~ above this kind of MAP sensor (as well as on the analog voltage kind sensors used by GM, Dodge, and some other makes), one in-range fail of the MAP sensor can reason issues there is no a MAP sensor password being set.

An problem with the MAP sensor can throw off your car’s air/fuel ratio.

An issue with the MAP sensor can throw off your car’s air/fuel ratio, top to increased fuel consumption.

Poor engine performance

A breakdown in the MAP/BARO sensor circuit may also influence the drivability of your vehicle. Your automobile may end up being hard come start, hesitate during acceleration, stall unpredictably, or experience rough idling.

How come Diagnose the P0108 Code

Now the we know what reasons a P0108 code and also its symptoms, the following step is identify which problem has triggered this code to it is in logged on your vehicle. Don’t hesitate to take it your auto to a professional if she unsure of performing the diagnosis.If you an knowledgeable DIY-er searching for advice ~ above testing and also fixing this trouble code yourself, here are some videos the may offer you a better idea the what the troubleshooting procedure might involve:

How to fix the P0108 Code

The P0108 code is a generic DTC, which way it’s sustained by miscellaneous makes and also models. While most vehicles will experience similar symptoms, the actions for diagnosis and repair might be different between auto models.

If you unsure around having sufficient technical knowledge to settle the code yourself, it’s finest to carry your automobile to the nearest auto repair shop for professional advice. If you decide on doing it on your own, repair manuals (like those indigenous Chilton) and also an ALLDATA vehicle subscription are great resources for manufacturing facility repair information.

Intake Manifold Pressure

There space a couple of basic types the fuel injection systems (pre-GDI). One of these is a “speed density” system, where there is a pressure sensor reading Intake manifold push (a.k.a., “manifold absolute pressure”) to determine engine load. The other type (not disputed in this article) is the Mass airflow (MAF) kind system. Part MAF systems also have a MAP sensor.

We speak a lot about intake manifold vacuum, yet MAP is usually a measurement of the differential in between ambient atmospheric pressure and also the push in the manifold.

Ambient atmospheric push at sea level measured in PSI is 14.7. In the metric system, it is 1 BAR.

That’s what we contact atmospheric pressure, and also it decreases v altitude. However the ECM/PCM measures barometric pressure and intake pressure in inch of mercury (that’s just how it’s measured, making use of a graduated tube and a set amount the mercury). Every PSI of pressure equals around 2 inches of mercury (Mercury is “Hg” on the periodic table).


If, because that example, barometric pressure is 30 inches of mercury and engine vacuum is 20 customs of mercury idling, then manifold absolute press is, at the point, 10 inch – i beg your pardon is the difference in between 30 inches and also the 20 inches of manifold vacuum. Manifold vacuum is created by the pistons developing low pressure as they take trip down on your intake strokes v the accelerator plate closed and airflow in ~ a minimum.

As the throttle plate opens and also the engine is loaded, manifold press increases and vacuum decreases. Thus, manifold press is specific indicator the engine load. That’s why some older automatic transmissions had actually a vacuum heat from the manifold connected to the transmission modulator valve come modify transmission shifts under load.

So, manifold absolute pressure is provided by the ECM/PCM to calculate engine load, which is the primary input the ECM/PCM offers to recognize fuel injector pulse width while the engine is law its work. The higher the measured MAP, the more comprehensive the fuel pulse through each injector event.

When the key is switched top top initially, the ECM/PCM records closed accelerator voltage, intake air and engine coolant temperature, and also barometric pressure using the MAP sensor. These factors determine just how much fuel is yielded when the engine is starting and after that fires up.

See more: How Many Pints In 3 Cups ? 3 C To Pt Conversion How Many Cups In A Gallon

Products pointed out in this Guide

Catalytic Converter
Barometric pressure Sensor
MAP Sensor

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