How To Test The MAP Sensor (1997-2003 4.0L Jeep Cherokee, Grand Cherokee, Wrangler)

The fastest and the most accurate way to test the manifold absolute pressure (MAP) sensor on your 4.0L equipped Jeep Cherokee (Grand Cherokee, Wrangler) is to bench-test it with a multimeter.

In this tutorial I'll show you how in a step-by-step way so that you can find out if the MAP sensor is bad (or not).

This tutorial will also help you diagnose codes: P0106, P0107, and P0108.

You can find this tutorial in Spanish here: Cómo Verificar El Sensor MAP (1997-2003 4.0L Jeep) (at: autotecnico-online.com).

NOTE: For the tutorial covering the MAP sensor test for the 1987 - 1995 4.0L equipped Jeeps, go here: How To Test The MAP Sensor (Jeep 4.0L).

MAP Sensor Diagnostic Essentials

What are the symptoms of a bad MAP sensor? The most obvious symptom that you'll see/experience, when the MAP sensor fails on your 4.0L Jeep Grand Cherokee (Cherokee, Wrangler) is the check engine light (CEL) lit on your instrument cluster and one or several of the following MAP sensor trouble codes:

• P0106: Manifold Absolute Pressure (MAP) System Performance.
• P0107: Manifold Absolute Pressure (MAP) Circuit Low Voltage.
• P0108: Manifold Absolute Pressure (MAP) Circuit High Voltage.

You'll also see one or more of the following:

• Bad gas mileage.
• Won't pass the emissions test.
• Black smoke coming out the tail pipe when the engine in your 4.0L Jeep Grand Cherokee (Cherokee, Wrangler) is running.

What tools do I need? The most important tool that you'll need is a multimeter.

Here's a list of the tools you'll need:

1. A vacuum pump.
   • The vacuum pump is not an absolute must, since you can use the good ol' lungs to apply vacuum to the sensor in TEST 1 of this tutorial.
   • If you don't have one and/or need to buy one, this is the one that I recommend and you can buy it here: MV8000 Automotive Tune-up and Brake Bleeding Kit.
2. Wire piercing probe.
   • Although this tool is not an absolute must, if you do buy one, you'll realize just how easy it makes testing the voltages inside the wires.
   • If you need to see what this tool looks like, you can see it here: Wire Piercing Probe.
3. Scan tool.
   • You don't need one to use the info in this article but how else are you gonna' check for the MAP sensor codes?
   • Don't have one? Check out my recommendation: Abe's Scan Tool Recommendation.

What does the MAP sensor do? The MAP sensor's job is to measure the pressure inside the intake manifold as the engine in your Jeep runs. Another name for this pressure is vacuum.

Your 4.0L Jeep Grand Cherokee's fuel injection computer will use the MAP sensor input, along with the inputs of the crank sensor and throttle position sensor (TPS) to calculate fuel injection and ignition timing (among several things).

The MAP sensor needs 3 inputs to be able to measure the amount of vacuum inside the intake manifold:

1. 5 Volts (power).
2. Ground.
3. Vacuum.

The descriptions below are of the MAP sensor.

MAP Sensor Pin Out
Pin	Description
1	Sensor Ground
2	MAP Sensor Signal
3	5 Volt Reference

Where To Buy The MAP Sensor And Save

Diagnosing The Jeep 4.0L MAP Sensor

Testing the MAP sensor on your 4.0L equipped Jeep Grand Cherokee (Cherokee, Wrangler) involves 3 specific tests, these are:

1. The first test is to see if the MAP sensor is creating a signal as you manually apply vacuum with a vacuum pump (or the good ol' lungs).
   • Go to: TEST 1: Checking The MAP Sensor Signal.
2. The second test is to make sure that the MAP sensor is getting fed power (5 Volts) on the .
   • Go to: TEST 2: Checking The 5 Volt Reference Circuit.
3. The third test and last test involves checking that the MAP sensor is getting Ground.
   • Go to: TEST 3: Verifying The MAP Sensor Is Getting Ground.

TEST 1: Checking For The MAP Sensor Signal

In this first test, we'll check that the MAP sensor on your 4.0L equipped Jeep Cherokee (Grand Cherokee, Wrangler) is producing a signal when vacuum is applied to its vacuum port.

The middle wire, of the MAP sensor's engine harness connector, is the one that carries the MAP signal (to the PCM) and it's this wire that you'll need to tap into with your multimeter.

NOTE: Although the instructions assume you're using a vacuum pump, if you don't have one, you can use your mouth and a vacuum hose to apply vacuum to the MAP sensor's vacuum port.

OK, this is what we'll do:

1. 1

   Remove the MAP sensor from the intake manifold (if you need to gain access to its vacuum port).
   
   Once you have removed it, reconnect it back to its electrical connector.

2. 2

   Select Volts DC on your multimeter.

3. 3

   Probe the middle wire of the MAP sensor with the red multimeter test lead.
   
   This is the wire that connects to the MAP sensor engine harness connector's terminal labeled with the number 2 in the illustration above.
   
   The best way to get to the signal inside the wire is using a wire piercing probe (to see what this tool looks like, click here: Wire-Piercing Probe).

4. 4

   Ground the black multimeter test lead on the battery's negative (-) terminal.

5. 5

   Connect your vacuum pump to the MAP sensor.

6. 6

   Turn the key to the ON position (don't start the engine).

7. 7

   Your multimeter should display: 4.8 V (this is no vacuum applied to the MAP sensor).

8. 8

   Apply vacuum. As you apply vacuum, your multimeter should read:

   1.  5 in Hg - 3.9V.
   2. 10 in Hg - 3.1V.
   3. 15 in Hg - 2.1V.

NOTE: What you're looking for, as you apply and release vacuum is for the multimeter to show a decrease in voltage (as you apply vacuum) and an increase in the voltage back to 4.5+ Volts (as you release vacuum).

Let's interpret your test results:

CASE 1: The MAP sensor's voltage decreased/increased as you applied/released vacuum. This tells you that the MAP sensor is OK and not the true cause of the MAP sensor codes.

This also confirms that the MAP sensor is getting power (5 Volts) on wire and Ground.

CASE 2: The MAP sensor's voltage DID NOT decrease/increase as you applied/released vacuum. This usually means that the MAP sensor is bad but we'll need to make sure that the MAP sensor is getting both power and Ground.

For this test, go to: TEST 2: Checking That The MAP Sensor Is Getting Power.