How to Test the MAP Sensor (P0107, P0108) (Dodge 3.9L, 5.2L, 5.9L)

How to Test the MAP Sensor (P0107, P0108) (Dodge 3.9L, 5.2L, 5.9L)

The manifold absolute pressure (MAP) sensor can be accurately tested with a multimeter and a vacuum pump and in this article I'll show you how.

When the MAP sensor goes BAD, you'll usually see one of the following diagnostic trouble codes stored in your Dodge's computer's memory: P0106, P0107, or P108. If this is the case, this is the article for you.

NOTE: This tutorial only covers the MAP sensor test on 1997 thru' 2003 Ram pickups/vans. For the MAP sensor test on 1994 thru' 1996 Ram pickups/vans, see the following tutorial:

  1. How to Test the MAP Sensor (1994-1996 Dodge Ram Pickup/Van).

This article is broken up into several different parts and so to help you navigate it a little easier, here are its contents at a quick glance:

  1. Symptoms of a BAD MAP Sensor.
  2. How the MAP Sensor Works.
  3. TEST 1: Verifying the MAP Signal.
  4. TEST 2: Verifying Power to the MAP Sensor.
  5. TEST 3: Verifying the MAP Sensor Ground Circuit.
  6. MAP Sensor Code Won't Go Away.
  7. Where to Buy the MAP Sensor and Save.
  8. Related Test Articles.

The following wiring diagram article may come in handy:

  1. 1996-1998 MAP Sensor Circuit Diagram (Dodge 3.9L, 5.2L, 5.9L).

Symptoms of a BAD MAP Sensor

When the manifold absolute pressure (MAP) sensor fails, the check engine light (CEL) will turn on and you'll see one of the following diagnostic trouble codes:

  1. P0107: MAP Sensor Voltage Too Low.
  2. P0108: MAP Sensor Voltage Too High.

Besides the diagnostic trouble codes, your Dodge pickup, van or SUV will experience one or several of the following symptoms:

  1. Rough idle.
  2. Black smoke coming out of the tail-pipe.
  3. Engine stalls under load.
  4. Engine dies as soon as it starts.
  5. Lack of power when you accelerate the vehicle down the road.

It's rare for the MAP sensor to go BAD but it doesn't mean they don't. What usually happens is that some other condition (affecting engine performance) fools the PCM (Powertrain Control Module = fuel injection computer) into thinking that the MAP sensor is BAD... so it's always a good idea to test it before replacing it.

In my experience, the absolute best way to test the MAP sensor is to bench test it (and this is how I'm gonna' show you how to tested in this article). By bench testing it, you can eliminate the other possibles that may be fooling the MAP sensor into sending a BAD signal to the PCM.

If after doing the MAP sensor test and the MAP sensor is good, then take a look at the section: MAP Sensor Code Won't Go Away.

How the MAP Sensor Works

The fuel system on your 3.9L, 5.2L, 5.9L is a ‘Speed Density’ type... which in lay man's terms means that it doesn't use a mass air flow (MAF) sensor to determine the amount of air that enters the engine.

In a ‘Speed Density’ fuel system, the PCM relies heavily on MAP sensor and engine RPM input to find out how much air the engine is breathing. Once it has calculated the amount of incoming air, it can then calculate the correct amount of fuel to inject (among several things).

OK, in a nutshell, cause I know you're probably itching to get testing, when you turn the key and crank the engine:

  1. The PCM supplies voltage to the MAP sensor. This power is the in form of 5 Volts.
    1. This voltage is provided thru' the wire labeled with the number 1.
  2. The PCM also provides ground to the MAP sensor
    1. This ground is provided thru' the wire labeled with the number 3.
  3. Once the MAP sensor gets power and ground, it now starts to measure the amount of vacuum the engine is producing.
  4. With both the MAP sensor signal info and crank sensor signal info, the PCM now calculates the approximate amount of air entering the engine and:
    1. Adjusts fuel injection pulse width and...
    2. Ignition timing.

Since the MAP sensor plays such a critical role in the performance and efficient operation of the engine in your pickup (van, SUV)... when it goes BAD, your vehicle is gonna' be in a world of hurt.

Dodge Vehicles:

  • B1500, B2500, B3500 3.9L, 5.2L, 5.9L
    • 1997, 1998
  • Dakota 3.9L, 5.2L, 5.9L
    • 1997, 1998, 1999
  • Durango 3.2L, 5.2L, 5.9L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003

Dodge Vehicles:

  • Ram 1500, 2500, 3500 3.9L, 5.2L, 5.9L
    • 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003
  • Ram Van 1500, 2500, 3500 3.9L, 5.2L, 5.9L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003

Jeep Vehicles:

  • Grand Cherokee 5.2L, 5.9L
    • 1997, 1998

“I came from a real tough neighborhood. Why, every time I shut
the window I hurt somebody’s fingers.”

Rodney Dangerfield

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