Manifold Air Pressure/Barometric Pressure Circuit High Input
P0108 is the code that is thrown when there is a problem with the Manifold Air Pressure (MAP) electrical circuit sensor. Typically, it means the MAP sensor is registering voltage flowing to the Engine Control Unit (ECU) that is too high.
This can be a problem because if the voltage going into the ECU is too high, then it is not in the correct optimal range of operations. This can cause the engine to not work well, specifically with the inputs from the Mass Air Flow Sensor (MAF) and Throttle Position Switch (TPS).
There are many different things that can possibly cause this error code:
There are several engine defects that can cause this issue. One of them is unmetered air entering the engine (usually as a result of a leak somewhere allowing extra air to come in). Another engine problem that can cause this code is a damaged catalytic converter, throwing off the vehicle’s emissions. A third engine problem that can cause this comes from misfired as a result of a poorly maintained engine.
Another area of concern could be related to defects in a variety of sensors. If either the MAP sensor, MAF sensor (in some vehicles), throttle position sensor or barometric sensor are defective, then you might see the P0108 code.
Another type of problem that can cause this issue has to do with your wiring. If you face open circuits, or wires that have been shortened, burnt or damaged, it can cause this message.
A final, but rare, cause of this error message is a defective Powertrain Control Module (PCM). Like we said, though, this is not a very common cause, so you should save it for last in your troubleshooting.
In the event of a P0108 code, you might notice one or more of the following symptomes:
The most obvious is the illuminated CHECK ENGINE light. Most likely, that light led you to check the trouble codes, which brought you here.
Assuming there’s an actual trouble, and not just a faulty code being thrown, you might also notice various performance issues. These include increased fuel consumption, difficulty starting, problems with acceleration, unpredictable stalling, a general lack of power and decrease in performance and/or rough idling.
Once the P0108 code is thrown, there are a series of steps you need to take to see what the actual problem is.
The first thing to do is make sure it’s not a faulty error code. To do this, clear the codes and then road-test the vehicle to see if it comes back. If you can, run live streaming data whil testing. This should verify there is a real error.
If the code comes back, the next step is a voltage test. Using multimeter, and with the key turned on, test to see how much voltage is going into the MAP. There should be 5 volts going in to the MAP, as well as a minimum of .5 to 1 volt when the throttle is closed.
While idling, you should also test the input to the ECU. There should be at least 1 volt of input at idle. Then, slowly increase your engine speed. If either a) there are more than 2 volts while idling, or b) the volts quickly go past 5 as you increase the engine speed, then most likely the MAP sensor is bad.
The most common mistake someone makes when diagnosing this error is not following the testing procedure. If you fail to follow the correct procedure, you might replace things that don’t need to be replaced, or vice versa.
So, verify the code first, then move on to the voltage inputs. Do not replace the MAP sensor or ECU or any other part until you can verify that the part in question is the real problem.
How serious is this?
The P0108 code signifies a problem that might not seem terrible at first, but if left unchecked can quickly escalate. Poor engine performance is a pain, and can lead to higher fuel consumption. If not fixed, though, this can quickly lead to rough operations, backfiring, difficulty starting and further damage that requires much more costly repairs in the long run.
What repairs can fix the code?
As stated above, the first thing to do is verify the code. Clear it from the system, perform a road test and see if it returns. Make sure to have a scanner attached during the test to livestream engine data.
If it returns, move on to checking the voltage for the MAP sensor. If it is not in the specifies range, that’s most likely you’re problem. Also, check the connectors and wiring, looking for shorts, areas that appear burnt or loose connections that could cause problems. Disconnect and reconnect various connections along the way to make sure they are tethered properly.
If you can not find any other reason to cause a voltage issue, then you are either looking at a problem with the MAP sensor, or the ECU itself. Replace the sensor first. If that doesn’t fix the issue, replace the ECU.