How To Test: P0108 OBD II Trouble Code (Honda 2.2L, 2.3L)

OBD II trouble code P0108 Manifold Absolute Pressure (MAP) Circuit High Voltage usually points to a bad MAP sensor that can no longer tell when the engine is under a load (when manifold vacuum is low).

Testing the MAP sensor on your Honda (or Acura) is not hard. In this tutorial I'll go over the basics you need to know to get to the bottom of the problem.

P0108 Basics You Need To Know

The PCM (Powertrain Control Module = Fuel Injection Computer) uses the MAP sensor to measure the amount of vacuum in the intake manifold.

As you're already aware, depending on how much you load the engine, by accelerating or decelerating it (or letting it idle), engine vacuum will either decrease or increase and the PCM, by measuring this amount of vacuum (among several other things), can know when to inject more or less fuel.

For example, if the engine's at idle, manifold vacuum is higher and the engine of course will need the PCM to inject less fuel into all its cylinders.

When the MAP sensor senses this high intake manifold vacuum, it produces a higher voltage signal that the PCM translates as the engine coming to an idle or you letting off of the accelerator pedal (i.e. as you're cruising down the road, among a few things).

If the engine is under load (like when accelerating down the highway), manifold vacuum will be less (than at idle) and the engine will need the PCM to inject more fuel (to meet the load demand).

When the MAP sensor senses this low intake manifold vacuum, it produces a lower voltage signal that the PCM now translates into adding more fuel to meet the demand of the load being placed on the engine.

As you already know, the MAP sensor has 3 wires in its connector. Each one has a specific job. Here's a brief description of the function of each:

1. One wire supplies 5 Volts DC.
   • This is the MAP sensor's power source.
   • The PCM (Powertrain Control Module = Fuel Injection Computer) provides these 5 Volts with the Key On Engine OFF (KOEO) or Key On Engine Running (KOER).
   • MAP sensor pin labeled with the number 1, in the image above, gets this power.
2. One wire feeds Ground.
   • In tech circles, this circuit is know as the low reference circuit.
   • The PCM provides this Ground internally.
   • Ground provided by the middle wire of the MAP sensor connector. MAP sensor pin labeled with the number 2, in the image above, gets this Ground.
3. One wire is the MAP sensor signal circuit.
   • This wire sends the signal the MAP sensor creates to the computer (PCM).
   • MAP sensor pin labeled with the number 3, in the image above, outputs this MAP signal to the PCM.

When a P0108 Manifold Absolute Pressure (MAP) Circuit High Voltage lights up the check engine light (CEL), on your 2.2L/2.3L equipped Honda, the PCM is letting you know that the MAP sensor's signal doesn't jive with actual engine operating conditions.

More specifically, that the MAP sensor is stuck reporting a high voltage.

Symptoms Of A P0108 Diagnostic Trouble Code

Since the PCM depends on the MAP sensor for engine load info (to inject more or less fuel into the engine cylinders), when it fails you'll see one or several of the following symptoms:

1. Check engine light (CEL) is shining nice and bright on the instrument cluster.
2. DTC P0108 is present.
3. Rough idle.
4. ‘Rotten egg’ smell coming from the exhaust.
5. Won't pass the state mandated emissions test.
6. Bad gas mileage.
7. Lack of power, rough idle, or hesitation.
8. Engine cranks a long time before starting.

Let's go to the next subheading and let's get testing!

Where To Buy The MAP Sensor

The following links will help you comparison shop for the MAP sensor (of known automotive name brands -no knock-off sensors):

If you're wondering if the MAP sensor will fit your particular Honda, don't worry. Once you get to the site, they'll ask you for the specifics of your particular Honda (or Acura) vehicle to make sure it fits. If it doesn't, they'll show you several that will. It's that easy to find the right part!

How To Diagnose Trouble Code P0108 Manifold Absolute Pressure (MAP) Circuit High Voltage

Testing and/or troubleshooting the MAP sensor on your 2.2L, 2.3L Honda isn't hard. This is a brief summary of the 3 tests in this tutorial:

1. Verifying The MAP sensor is getting power.
   • We'll use a multimeter to make sure the MAP sensor is getting 5 Volts DC from the PCM. This is a very simple and easy test.
   • TEST 1: Verifying The MAP Sensor Has Power.
2. Verify that the MAP sensor has a good path to Ground.
   • We'll be using a multimeter to verify this Ground path.
   • TEST 2: Verifying The MAP Sensor Has Ground.
3. Manually apply and release vacuum to see if the MAP sensor responds to these changes in pressure.
   • You can either use a vacuum pump or the good ole' lungs for this simple test.
   • TEST 3: Bench Testing The MAP Sensor.

I recommend that you start with TEST 1: Verifying The MAP Sensor Has Power, but you can modify the following tests to fit your particular diagnostic needs.