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P0108 Severity
Identifying an OBD code is just the start of a complete diagnostic routine. Most trouble codes are caused by a sensor reporting a value that is out of range. Just replacing a sensor may not fix underlying issues. Be sure to understand the code, the part or system in your car that the code refers to, and the risks of delaying professional repair.
Proper diagnosis will save you time and money on unnecessary repairs.
Urgent codes indicate immediate action is necessary. These are urgent and significant malfunctions that can cause severe damage to the vehicle or harm the driver and passengers.
The Manifold Absolute Pressure Sensor/Barometric Pressure Sensor measures the rise and fall of the air pressure inside the Intake Manifold. The engine control module (PCM) uses this information to determine how much fuel to use to keep the engine running properly. When the PCM detects a problem with this sensor or the circuit for the sensor, it will set code P0108.
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OBD-II Code P0108 is defined as a Manifold Absolute Pressure Sensor/Barometric Pressure Circuit High Input
The Manifold Absolute Pressure Sensor/Barometric Pressure Sensor measures the rise and fall of the air pressure inside the Intake Manifold. This provides critical data needed for the Powertrain Control Module(PCM) to control the Air Fuel Ratio, the Ignition Spark Timing and many components of the Emission Control Systems.
Code P0108 sets when the voltage to the PCM from the MAP/Baro Sensor Circuit stays above 4.5 volts for 10 seconds or more when the values from the Throttle Position, RPM and Oxygen sensors are changing.
When diagnosing a P0108 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive while paying close attention to engine load, throttle position, RPM, and road speed on a data streaming scan tool. As you drive the vehicle, compare these values to the MAP Sensor PID or parameter ID. The MAP Sensor voltage values should rise and fall with changes in engine speed and engine load. Typically the values will vary from 4 volts or more when accelerating to 1 volt or less when decelerating.
Check the MAP sensor connector with the key on and the engine off. There needs to be a steady 5 volt reference voltage and a very good ground. The third wire will be the MAP Sensor signal wire which sends data to the Power Train Control Module. Find and use the proper engine performance wiring diagram to discern the proper color and position of these wires in the connector.
It never hurts to do a key on-engine off vacuum pump voltage output test of the MAP sensor. You should watch the output on the scan tool as this will verify the harness and connections as well. The voltage should steadily decrease from 5 volts to less than 1 volt as you apply 18-20 inches of vacuum. I also like to wiggle the MAP sensor wiring harness as I apply vacuum to ensure that the MAP sensor wiring and/or connector aren't contributing to the problem. Always inspect the MAP Sensor vacuum hose and if the MAP sensor plugs directly into the intake manifold, be sure to check its seal, as they can split and cause erratic readings.