How To Test The MAP Sensor (1999-2001 4.7L V8 Grand Cherokee)

When the MAP sensor in your 1999–2001 4.7L V8 Jeep Grand Cherokee fails, it'll usually trigger a P0106, P0107, or P0108 diagnostic trouble code (DTC).

The cool thing is you can test it without a scan tool or any other expensive diagnostic equipment.

In this tutorial, I'll show you how to check it with a multimeter. This simple (and easy) test will accurately tell you if the MAP sensor is bad and if so, resolve the engine performance issue and the MAP sensor DTC lighting up the check engine light.

APPLIES TO: This tutorial applies to the following vehicles:

• 4.7L V8 Jeep Grand Cherokee: 1999, 2000, 2001.

TPS SENSOR DIAGNOSTICS:

• How To Test The Throttle Position Sensor (1999-2004 4.7L V8 Jeep Grand Cherokee).

Symptoms Of A Bad MAP Sensor

The fuel system on your 4.7L Jeep Grand Cherokee is a 'speed density' type. Which, in layman's terms, means that it needs 3 inputs to calculate the amount of fuel to inject for any given amount of air entering the engine. These 3 inputs are engine speed, engine vacuum (manifold pressure), and air intake temperature.

The MAP sensor is the one that provides the engine vacuum (manifold pressure) input to your Grand Cherokee's fuel injection computer. Since it's such a critical input sensor, when the it fails, it causes quite a bit of havoc on engine performance.

The most obvious symptom, of a failed MAP sensor, is the check engine light (CEL) will be shining nice and bright (and a MAP sensor trouble code stored in the PCM's memory). But it's not the only one. You may see one or more of the following symptoms:

• Diagnostic trouble codes (DTCs):
  • P0106: Manifold Absolute Pressure Sensor Performance.
  • P0107: Manifold Absolute Pressure Sensor (MAP) Circuit Low.
  • P0108: Manifold Absolute Pressure Sensor (MAP) Circuit High.
• Doesn't pass the smog check.
• Engine idles rough.
• Engine takes forever to start (extended cranking time).
• Engine doesn't start.
• Black smoke coming out of the tail-pipe as engine runs.

Where To Buy The MAP Sensor And Save

You can find the MAP sensor just about in anywhere. The best place to buy it and save a few bucks is is online.

The following links will help you comparison shop for the MAP sensor:

NOTE: Not sure if the MAP sensor fits your particular vehicle? Don't worry, once you get to the site they'll make sure it fits by asking you the specifics of your particular vehicle. If it doesn't fit, they'll find you the right MAP sensor.

TEST 1: Checking The MAP Sensor Signal

In a nutshell, to test the MAP sensor we need to connect a multimeter to its signal wire and apply vacuum to it while we read the signal wire voltage output.

Now, we're not gonna' use the engine's vacuum to test it. We're gonna' manually apply this vacuum with a vacuum pump. Why? Because applying vacuum with a vacuum pump and bypassing the engine's vacuum is the most accurate way of testing the MAP sensor.

By the way, the dark green with orange stripe (DK GRN/ORG) wire is the one that transmits the MAP signal to the PCM and is the one we'll tap into with the multimeter.

Don't worry, this is a pretty easy test and in you'll find it all explained in a step-by-step manner below.

If you don't have a multimeter or a vacuum pump, these are the ones I recommend:

• Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (Amazon affiliate link).
• HTOMT 2 In 1 Vacuum Pump Test Set (Amazon affiliate link).

NOTE: The vacuum inlet port on the MAP sensor is larger than the hose that typically comes with a handheld vacuum pump. To connect them, you'll need some kind of adapter. I use an old spark plug boot from a discarded plug wire —it fits snugly and does the job perfectly. You can use anything similar to step up or step down the hose size as needed.

OK, these are the test steps:

1. 1

   Remove the MAP sensor from its place on the intake manifold.

2. 2

   Connect your vacuum pump to the MAP sensor's vacuum port using a vacuum hose.
   
   NOTE: Before you proceed to the next step, make sure the MAP sensor is connected to its connector.

3. 3

   Set your multimeter to Volts DC mode.

4. 4

   Connect the black multimeter test lead directly to the battery negative (-) terminal.

5. 5

   Connect the red multimeter test lead to the DK GRN/ORG wire of the MAP sensor connector.
   
   NOTE: You'll need to either use a back probe on the connector or a wire piercing probe on the wire to access the signal (inside the wire).

6. 6

   Turn the key ON but don't start the engine. At this point your multimeter should register about 3.8 to 4.0 Volts DC.

7. 7

   Pump the vacuum pump to apply vacuum to the MAP sensor.

8. 8

   The voltage should drop down to 1.1 Volts with vacuum applied to the sensor.

9. 9

   Release the vacuum completely.

10. 10

    The voltage should rise again, returning to the original 3.8–4.0 Volt range with vacuum to the sensor released.

11. 11

    Repeat applying and releasing vacuum to the sensor several times. Each time, you should see the voltage decrease and increase.

OK, let's take a look at what your vacuum pump test results mean:

CASE 1: Your multimeter registered the indicated voltages as you applied vacuum. This tells you that the manifold absolute pressure sensor is OK (not defective).

Now, if your vehicle still has the MAP sensor code lighting up the check engine on your instrument cluster, take a look at the section: MAP Sensor Code Won't Go Away for more info.

CASE 2: Your multimeter registered voltage, but it did not increase or decrease as you applied vacuum. This usually means the MAP sensor on your 4.7L V8 Jeep Grand Cherokee is bad.

To be sure the MAP sensor is bad, we need to make sure it's getting power and Ground. For the first of these two tests, go to: TEST 2: Making Sure The MAP Sensor Is Getting Power.

CASE 3: Your multimeter registered 0 Volts. This usually means that the MAP sensor is fried.

To be absolutely sure, we've got to make sure the MAP sensor has power and Ground. If both (power and Ground) are present, the MAP sensor is bad. For the first of those two tests, go to: TEST 2: Making Sure The MAP Sensor Is Getting Power.

TEST 2: Making Sure The MAP Sensor Is Getting Power

In this test section, we're gonna' make sure that the MAP sensor is being fed with power, which is in the form of 5 Volts.

These 5 Volts are provided by your Grand Cherokee's PCM and are delivered by the orange (ORG) wire of the MAP sensor's 3-wire connector.

We'll do a simple multimeter voltage test on the terminal that connects to the ORG wire to confirm that it's actually supplying this voltage.

NOTE: This test is done by probing the front of the female terminal of the connector. Be careful when probing the terminal to avoid damaging it.

This is what you need to do:

1. 1

   Disconnect the MAP sensor from its 3-wire connector.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Connect the black multimeter test lead to the battery negative (-) post.

4. 4

   With red multimeter test lead, probe the female terminal of the connector that corresponds to the ORG wire.

5. 5

   Turn the key to the ON position but don't crank or start the engine.

6. 6

   Your multimeter should read 4.5 to 5 Volts DC.

Let's take a look at what your test results mean:

CASE 1: The multimeter confirms that the MAP sensor is getting 5 Volts. This is the correct and expected test result.

Now that we've confirmed the MAP sensor is getting power, our next step is to make sure it's getting Ground. For this test, go to: TEST 2: Making Sure The MAP Sensor Is Getting Power.

CASE 2: The MAP sensor isn't getting power. Double check that you're testing the correct MAP sensor connector terminal and repeat the test.

If your multimeter still doesn't report 4.5 to 5 Volts DC, then the most likely cause of this missing voltage is an open-circuit or short-circuit problem in the ORG wire between the MAP sensor connector and the PCM.

In this case, the MAP sensor isn't the problem (and replacing it won't help) since without power, it's not going to function.

Although it's beyond the scope of this tutorial, your next step is to check the continuity of the ORG wire between the MAP sensor connector and the PCM connector.

TEST 3: Making Sure The MAP Sensor Is Getting Ground

So far, your test have confirmed:

• The MAP sensor's output voltage signal does not decrease/increase as you apply/release vacuum (TEST 1).
• The MAP sensor is getting 4.5 to 5 Volts delivered by the ORG wire (TEST 2).

In this test section, we're gonna' make sure that the MAP sensor is being fed with Ground.

The MAP sensor gets Ground from the PCM via the black with light blue stripe BLK/LT BLU wire.

To confirm that the BLK/LT BLU wire is delivering Ground (from the PCM), we're gonna do a simple multimeter voltage test.

Let's get going:

1. 1

   Disconnect the MAP sensor from its 3-wire connector.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Connect the black multimeter test lead to the battery negative (-) post.

4. 4

   Connect the black multimeter test lead (using the appropriate tool) to BLK/LT BLU wire.

5. 5

   Turn the key to the ON position but don't crank or start the engine.

6. 6

   Your multimeter should read 4.5 to 5 Volts DC.

Let's break down what that result tells us:

CASE 1: The multimeter confirms that the MAP sensor is getting Ground. This is the correct and expected test result.

You can conclude that the MAP sensor is bad only if you've confirmed that:

• The MAP sensor is not providing a varying voltage signal when manually applying/releasing vacuum to it (TEST 1).
• The MAP sensor is being fed 5 Volts DC (TEST 2).
• The MAP sensor is being fed Ground in this test section.

If you're ready to replace the manifold absolute pressure sensor, these are the two sensors I recommend from known automotive brands that I have been using for years and that I don't hesitate to recommend:

• Standard Motor Products AS141 Map Sensor (Amazon affiliate link).
• A-Premium Manifold Pressure (MAP) Sensor (Amazon affiliate link).

CASE 2: The MAP sensor isn't getting Ground. Double check that you're testing the correct MAP sensor connector terminal and repeat the test.

If your multimeter still doesn't report Ground, then the most likely cause of this missing Ground is an open-circuit or short-circuit problem in the BLK/LT BLU wire between the MAP sensor connector and the PCM.

In this case, the MAP sensor isn't the problem (and replacing it won't help) since without Ground, it's not going to function.

Although it's beyond the scope of this tutorial, your next step is to check the continuity of the BLK/LT BLU wire between the MAP sensor connector and the PCM connector.

MAP Sensor Code Won't Go Away

Over the years I've learned that quite a few conditions can cause the PCM to think the MAP sensor is bad when it isn't.

Below, I've highlighted the two most common problems I've run across that have caused a MAP sensor code (when the MAP sensor was good):

1. Low engine compression condition:
   • You can check this by doing an engine compression test.
2. Low fuel pump pressure condition:
   • Check fuel pump pressure with a fuel pressure gauge. A failing fuel pump will cause a lean air fuel mixture that can set a MAP sensor trouble code.
3. The fuel injection computer is bad (internal short). Although this problem is not very common, it does happen.
4. Check the MAP sensor's connector for damage. The most common problem with the connector is the locking tab has broken. This causes the connector to work itself loose, causing an intermittent false connection.

Before you jump the gun and start replacing the above, test the components first. This will help you save time, money, and the frustration of replacing parts your 4.7L Jeep Grand Cherokee does not need.