P0108 MAP Sensor OBD II Trouble Code (Chrysler 2.0L, 2.4L)

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).

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,
   • The throttle plate opens and intake manifold vacuum decreases.
   • The MAP sensor's voltage signal increases to correspond to the decrease in manifold vacuum.
   • 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,
   • The throttle plate closes and intake manifold vacuum increases.
   • The MAP sensor's voltage signal decreases to correspond to the increase in manifold vacuum.
   • 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

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

How The 4-Wire MAP Sensor Works

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

Symptoms Of A P0108 Diagnostic Trouble Code

As I mentioned in the previous page, the fuel system (which is a speed density type) in your Chrysler (Dodge, Plymouth, etc.) car or mini-van needs to know how much load the engine is under.

The PCM gets this engine load info from the MAP sensor's vacuum readings.

So when the PCM receives a MAP signal that doesn't match the actual engine operating conditions, it's not gonna' want to play ball and you'll feel it in more ways than one.

When the MAP sensor fails, you'll see one or more of the following symptoms:

1. Check engine light (CEL) is lit.
2. DTC P0108 is registered in the PCM memory.
3. Vehicle doesn't pass the state mandated emissions test.
4. Bad gas mileage.
5. Hard start and/or extended cranking time (after shut off).
6. Black smoke coming out of the tailpipe.
7. Hesitation when accelerating your car or mini-van.
8. Rough idle.
9. Engine stalls as soon as you let off the gas pedal.

Let's find out what are the common causes of a P0108 DTC, in the next subheading.

Common Causes Of A P0108 Trouble Code

The most common causes of trouble code P0108 are:

1. A bad manifold absolute pressure (MAP) sensor.
2. A broken MAP sensor connector.
3. A problem in the sensor 3 or 4 wires. Specifically, a short in one of them.
4. A worn out engine that has very low or uneven engine compression.
5. A fuel pump that's failing and not supplying enough fuel volume.
6. A timing belt that's been installed incorrectly (timing marks not lining up).
7. A bad PCM.

Although extremely rare for this to happen, a bad PCM can also cause a false P0108 trouble code.

Troubleshooting DTC P0108

What's gonna make P0108 manifold Absolute Pressure (MAP) Circuit High Voltage OBD II diagnostic trouble code (DTC) make sense, is to remember that the PCM sees the manifold absolute pressure (MAP) sensor (MAPS) stuck producing a high voltage signal that corresponds to an engine that seems stuck at high RPMs and/or a big throttle angle.

If you recall, from the previous page:

1. The MAP sensor's voltage signal increases when the throttle plate opens and manifold vacuum is lower.
2. The MAP sensor's voltage signal decreases when the throttle plate closes and manifold vacuum is higher.

Just to recap the info in this tutorial, when a DTC P0108 is registered, the PCM sees the MAP sensor reporting a low intake manifold vacuum pressure (and thus receiving a high voltage MAP signal) when it knows, via other sensor inputs, that it should be reporting a higher vacuum pressure (and thus lower voltage signal).

Confused yet? Don't worry, the MAP sensor test is very, very easy. By manually testing the MAP sensor with a multimeter, you and I can find out if it's truly fried or not.

You can find the MAP sensor tests here:

• 3-wire MAP Sensor Test:
  • 3-Wire MAP Sensor Diagnostic Test Chrysler, Dodge, Plymouth (at: easyautodiagnostics.com).
• 4-wire MAP Sensor Test:
  • Chrysler 4-Wire MAP Sensor Diagnostic Test (at: easyautodiagnostics.com).