Richard McCuistian, ASE Certified Master vehicle Technician

Technical Reviewer at

Written by Staff authors - update on respectable 12th, 2021

When the ECM/PCM detects a difficulty with the signal sent by the Manifold Absolute push (MAP) sensor the P0108 code will be save on computer by the ECM/PCM. Learn more about this code in the following guide.

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What does the P0108 password Mean?

Diagnostic trouble password (DTC) P0108 code means “Manifold absolute Pressure/Barometric press High.” that is motivated by the ECM as soon as it obtain a signal indigenous the MAP/BARO sensor circuit the is over the typical range.

Typically, the MAP/BARO sensor is supplied with regulated volts by the ECM ~ above a 5-volt reference circuit. Enlarge Fords usage a three-wire sensor that uses 5 volts, but the output signal isn’t a voltage, it’s a frequency. In ~ sea level v the engine off and also the key on, a Ford MAP sensor typically reads around 158 hertz, however when the engine starts, the frequency drops to around 110 hertz. On this type of MAP sensor (as well together on the analog voltage form sensors offered by GM, Dodge, and also some various other makes), one in-range fail of the MAP sensor can reason issues without a MAP sensor password being set.

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

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

Poor engine performance

A break down in the MAP/BARO sensor circuit might also impact the drivability of her vehicle. Your automobile may become hard to start, hesitate throughout acceleration, stall unpredictably, or suffer rough idling.

How come Diagnose the P0108 Code

Now that we understand what causes a P0108 code and also its symptoms, the following step is identifying which problem has motivated this password to it is in logged on her vehicle. Don’t hesitate to take it your automobile to a professional if you unsure of performing the diagnosis.If she an proficient DIY-er searching for advice on testing and fixing this trouble code yourself, right here are part videos that may offer you a better idea that what the troubleshooting procedure might involve:

How to solve the P0108 Code

The P0108 code is a generic DTC, which means it’s sustained by various makes and also models. While many vehicles will certainly experience comparable symptoms, the steps for diagnosis and repair may be various between car models.

If you unsure about having enough technical understanding to fix the password yourself, it’s best to bring your auto to the nearest auto repair shop for skilled advice. If you decide on doing the on your own, repair manuals (like those from Chilton) and an ALLDATA automobile subscription are good resources for factory repair information.

Intake Manifold Pressure

There space a couple of simple types that fuel injection systems (pre-GDI). Among these is a “speed density” system, whereby there is a push sensor analysis Intake manifold push (a.k.a., “manifold absolute pressure”) to recognize engine load. The other kind (not questioned in this article) is the Mass air flow (MAF) form system. Some MAF systems additionally have a MAP sensor.

We talk a lot around intake manifold vacuum, but MAP is usually a measure up of the differential between ambient atmospheric pressure and also the push in the manifold.

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

That’s what we call atmospheric pressure, and it decreases v altitude. However the ECM/PCM steps barometric pressure and also intake pressure in inches of mercury (that’s how it’s measured, using a i graduated tube and a collection amount of mercury). Each PSI of push equals around 2 inches of mercury (Mercury is “Hg” top top the regular table).


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

As the accelerator plate opens and also the engine is loaded, manifold press increases and also vacuum decreases. Thus, manifold push is an accurate indicator the engine load. That’s why part older automatically transmissions had a vacuum heat from the manifold associated to the infection modulator valve to modify transmission shifts under load.

So, manifold absolute press is used by the ECM/PCM to calculation engine load, i beg your pardon is the main input the ECM/PCM supplies to determine fuel injector pulse broad while the engine is doing its work. The higher the measured MAP, the broader the fuel pulse with each injector event.

When the crucial is switched top top initially, the ECM/PCM records closed throttle voltage, entry air and also engine coolant temperature, and barometric press using the MAP sensor. These components determine just how much fuel is ceded when the engine is beginning and after the fires up.

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Products discussed in this Guide

Catalytic Converter
Barometric pressure Sensor
MAP Sensor

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