How To Test The MAP Sensor (1994-1997 2.2L Chevrolet S10, GMC Sonoma)

TEST 2: Making Sure The MAP Sensor Is Getting 5 Volts

The MAP sensor needs power and Ground to function. Without them, the MAP sensor will not function.

The focus of this test section is to make sure that it's receiving power in the form of 5 Volts from the fuel injection computer.

The wire that delivers these 5 Volts to the sensor is the gray (GRY) wire of the MAP sensor's 3-wire connector.

If your test result confirms the MAP sensor receives 5 Volts, your next step is to make sure that it's getting Ground in TEST 3.

Let's get started:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Disconnect the MAP sensor from its electrical connector.

3. 3

   Probe the wire that connects to the terminal labeled with the number 1 in the illustration above with the red multimeter test lead.
   
   The wire that connects to terminal 2 is the GRY wire of the 3-wire connector.
   
   NOTE: You can probe the front of the wire's female terminal. If you do, be careful not to damage it with your multimeter's probe.

4. 4

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

5. 5

   Turn the key ON but don't start the engine.

6. 6

   Your multimeter should show you a voltage value around 4.5 to 5 Volts DC.

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

CASE 1: The multimeter registered 5 Volts. This is the correct and expected test result.

Now that you have confirmed the MAP sensor is receiving power, your next step is to make sure that it's getting Ground. Go to: TEST 3: Making Sure The MAP Sensor Is Getting Ground.

CASE 2: The multimeter DID NOT register 5 Volts. Without power, the MAP sensor will not function.

Although it's beyond the scope of this tutorial, your next step is to find out why these 5 Volts are missing and restore them. Once you restore power to the MAP sensor, it'll start functioning again.

TEST 3: Making Sure The MAP Sensor Is Getting Ground

So far, the previous two tests have confirmed:

• The MAP sensor's output voltage signal does not decrease/increase as you apply/release vacuum to the sensor (TEST 1).
• The MAP sensor is receiving 5 Volts from the gray wire (TEST 2).

In this last test section, we'll focus our diagnostic efforts on making sure that the MAP sensor receives Ground from the fuel injection computer.

The wire that delivers Ground to the MAP sensor is the black (BLK) wire of the MAP sensor's 3-wire connector and it connects to the terminal labeled with the number 3 in the illustration above.

IMPORTANT: The fuel injection computer is the component that supplies Ground to the MAP sensor. Be careful and do not short-circuit the Ground wire to 12 Volts or you'll fry the computer. The suggested multimeter voltage test is a safe way to test for the presence of Ground in the wire.

These are the test steps:

1. 1

   Place your multimeter still in Volts DC mode.

2. 2

   Disconnect the MAP sensor from its electrical connector.

3. 3

   Probe the wire labeled with the number 3 in the image above, with the black multimeter test lead.
   
   The wire that connects to terminal 3 is the BLK wire of the 3-wire connector.
   
   NOTE: You can probe the front of the wire's female terminal. If you do, be careful not to damage it with your multimeter's probe.

4. 4

   Connect the red multimeter test lead on the battery's positive (+) post.

5. 5

   Turn the key ON but don't start the engine.

6. 6

   Your multimeter register 10 to 12 Volts DC.

OK, let's see what your test result means:

CASE 1: The multimeter registered 10 to 12 Volts. This is the correct test result and tells you that the MAP sensor is receiving Ground.

You can correctly conclude the manifold absolute pressure sensor is bad and needs replacement if you have:

• Confirmed the MAP sensor voltage signal does not decrease/increase as you apply/release vacuum to the sensor (TEST 1).
• Confirmed the MAP sensor is receiving 5 Volts (TEST 2).
• Confirmed the MAP sensor is receiving Ground (this test section).

CASE 2: The multimeter DID NOT register 10 to 12 Volts. Without Ground, the MAP sensor will not function.

Although it's beyond the scope of this tutorial, your next step is to find out why the MAP sensor is not receiving Ground and resolve the problem. Once you restore Ground to the MAP sensor, it'll start functioning again.

MAP Sensor Code Won't Go Away

Quite a few different things can fool the fuel injection computer into thinking that the manifold absolute pressure sensor has failed (when it hasn't).

So if you've tested the MAP sensor and confirmed it's functioning correctly, yet the MAP sensor trouble code keeps returning, take a look at the following testing suggestions:

1. The o-ring (rubber gasket) on the vacuum inlet of the MAP sensor is missing or cracked.
2. The engine has several cylinders with very low engine compression causing it to idle rough and thus producing low or erratic vacuum. For this I suggest an engine compression test.
   • How To Test Engine Compression (1994-2003 2.2L Chevrolet S10, GMC Sonoma).
3. The MAP sensor is failing intermittently. Which means that it works fine most of the time, but every now and then it doesn't:
   • I have found that the best way to test these intermittent problems is to slightly tap the MAP sensor with the handle of a screw-driver and see if this tapping screws up the voltage readings as I apply vacuum.
4. The MAP sensor's connector is bad, usually the locking tab is broken and the connector has worked itself loose, causing an intermittent false connection.
5. Your fuel pump is starting to go bad and is not sending enough fuel and/or fuel pressure up to the fuel injectors. I suggest a fuel pump pressure test.