Troubleshooting P0108 Diagnostic Trouble Code (Chrysler, Dodge, Plymouth)

OBD II trouble code P0108 Manifold Absolute Pressure (MAP) Circuit High Voltage points to a manifold absolute pressure (MAP) sensor that's reporting a continuous low intake manifold vacuum pressure condition regardless of present engine operating conditions.

In other words... the MAP sensor is stuck showing the engine under load, when it isn't. This could be due to MAP sensor failure or a mechanical problem with the engine.

In this tutorial, I'll show you what a P0108 DTC means and how the MAP sensor works... all in plain English. I'm also gonna' show you where you can find the 3-wire and 4-wire MAP sensor test tutorials that'll show you how to test the MAP sensor with a multimeter (no scan tool required).

Here are the contents of this tutorial at a glance:

  1. P0108 MAP Sensor Basics.
  2. How the 3-Wire MAP Sensor Works.
  3. How the 4-Wire MAP Sensor Works.
  4. Symptoms of a P0108 Diagnostic Trouble Code.
  5. Common Causes of a P0108 Trouble Code.
  6. Troubleshooting DTC P0108.

P0108 MAP Sensor Basics

Your Chrysler's fuel system is a speed density type. Which in layman's terms means that the fuel injection computer uses engine speed and engine load to control the amount of fuel injection and ignition spark advance (the feature all speed density type fuel systems share is a lack of a mass air flow (MAF) sensor).

How does the PCM (Powertrain Control Module = fuel injection computer) know how much load the engine is under? Via the manifold absolute pressure (MAP) sensor.

The MAP sensor is tasked with measuring the ever changing vacuum pressure inside the intake manifold and sends the info to the PCM as a volts DC signal.

We can sum this up as: The bigger the engine load (i.e. accelerating your car or mini-van to pass someone on the highway), the smaller the voltage signal the MAP sensor creates. The smaller the engine load (think coming to a stop light and the engine idling), the higher the voltage signal the MAP sensor creates and sends to the PCM.

To drive this point home a little further, I'll explain it like this:

  1. As you step on the accelerator pedal,
    1. The throttle plate opens and intake manifold vacuum decreases.
    2. The MAP sensor's voltage signal increases to correspond to the decrease in manifold vacuum.
    3. The fuel injection computer now ‘sees’ the engine's load increase and injects more fuel.
  2. As you let your foot off the accelerator pedal,
    1. The throttle plate closes and intake manifold vacuum increases.
    2. The MAP sensor's voltage signal decreases to correspond to the increase in manifold vacuum.
    3. The fuel injection computer now ‘sees’ the engine's load decrease and injects less fuel.

Now, when the MAP sensor stays stuck producing a high voltage signal, that indicates a low vacuum condition, even though other sensor inputs indicate otherwise... the PCM sets a code P0108 Manifold Absolute Pressure (MAP) Circuit High Voltage.

How the 3-Wire MAP Sensor Works

Troubleshooting P0108 Diagnostic Trouble Code (Chrysler, Dodge, Plymouth)

The difference between a Chrysler 3-wire and 4-wire MAP sensor is the fact that the 3-wire doesn't have an intake air temperature (IAT) sensor bundled in the same unit/case (like the 4-wire does).

Each of the manifold absolute pressure (MAP) sensor's 3 wires has a specific task since one feeds power, another feeds ground and the remaining one feeds the PCM the sensor creates.

To be able to test the MAP sensor (using a multimeter), you need to know which one is which.

Here's a brief description of the 3 manifold absolute pressure MAP sensor circuits:

  1. Wire labeled with the number 1.
    1. Feeds ground to the MAP sensor.
    2. Ground is provided by the PCM (internally).
  2. Wire labeled with the number 2.
    1. Supplies power to the MAP sensor.
    2. In the form of 5 Volts DC and is supplied only with Key On Engine Off (KOEO) or Key On Engine Running (KOER).
    3. The PCM supplies these 5 Volts DC.
  3. Wire labeled with the number 3.
    1. Feeds the MAP voltage signal to the PCM.
    2. This voltage signal increases or decreases depending on the manifold vacuum that's created by the throttle angle.
    3. At Key On Engine Off (KOEO), the MAP voltage signal is 4.5 Volts.
    4. As vacuum increases, MAP signal voltage decreases.
    5. As vacuum decreases, MAP signal voltage increases.

The 3-wire MAP sensor can be easily and accurately tested with a multimeter. You can find the 3-wire MAP sensor test here: MAP Sensor Diagnostic Test Chrysler, Dodge, Plymouth (at: easyautodiagnostics.com).

How the 4-Wire MAP Sensor Works

Troubleshooting P0108 Diagnostic Trouble Code (Chrysler, Dodge, Plymouth)

The 4-wire MAP sensor is two sensors in one. One part of the sensor measures the manifold absolute pressure (vacuum).

The other part of the sensor measures the intake air temperature and is known as the IAT sensor.

Just like the basic 3-wire sensor... the MAP part of this dual sensor has 3 circuits... that feed it power, ground, and one that returns the signal the sensor creates to the PCM.

Don't worry... it's not as hard as it sounds:

  1. Wire labeled with the number 1.
    1. Feeds ground to the MAP sensor.
    2. Ground is provided by the PCM (internally).
  2. Wire labeled with the number 2.
    1. IAT sensor 5 Volt Reference Circuit.
  3. Wire labeled with the number 3.
    1. Supplies power to the MAP sensor.
    2. In the form of 5 Volts DC and is supplied only with Key On Engine Off (KOEO) or Key On Engine Running (KOER).
    3. The PCM supplies these 5 Volts DC.
  4. Wire labeled with the number 4.
    1. Feeds the MAP voltage signal to the PCM.
    2. This voltage signal increases or decreases depending on the manifold vacuum that's created by the throttle angle.
    3. At Key On Engine Off (KOEO), the MAP voltage signal is 4.5 Volts.
    4. At Key On Engine Off (KOEO), the MAP voltage signal is 4.5 Volts.
    5. As vacuum increases, MAP signal voltage decreases.
    6. As vacuum decreases, MAP signal voltage increases.

The 4-wire MAP sensor can be easily and accurately tested with a multimeter. I've written such a tutorial and ou can find the 4-wire MAP sensor test here: Chrysler 4-Wire MAP Sensor Diagnostic Test (at: easyautodiagnostics.com).