How To Test The Isuzu Manifold Absolute Pressure (MAP) Sensor

TEST 2: Checking The MAP Sensor's Power Circuit

So far, in MAP TEST 1, you have verified that the MAP sensor on your Isuzu pickup or SUV is not creating a signal that decreases/increases as you applied/released vacuum to it.

This could be due to a lack of power and Ground. In this part, you'll check to see if the MAP sensor is being fed with power.

This power comes in the form of 5 Volts and the PCM (Powertrain Control Module = Fuel Injection Computer) is the one that provides this juice.

Alright, this is what you'll need to do:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Turn the key on but don't crank or start the engine.

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.

4. 4

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

5. 5

   Your multimeter should show 4.5 to 5 Volts DC.

OK, now that the testing part is done, let's take a look at what your results mean:

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

It's starting to look like the MAP sensor is bad but you still need to check that the MAP sensor is getting Ground. For the Ground test, go to: TEST 3: Checking The MAP Sensor's Ground Circuit.

CASE 2: The multimeter DID NOT register 5 Volts. This result lets you know that the MAP sensor is not getting power and without power, it won't work. So then, this result also eliminates the MAP sensor itself as bad.

Although it's beyond the scope of this article to troubleshoot the cause of these missing 5 Volts, you have now eliminated the MAP sensor as bad. Resolving the issue that is keeping these 5 Volts from being supplied will solve the MAP sensor issue on your Isuzu pickup or SUV.

TEST 3: Checking The MAP Sensor's Ground Circuit

So far, you've tested the MAP sensor signal (TEST 1) and checked that the MAP sensor is getting power (TEST 2).

The next step is to make sure that the MAP sensor on your Isuzu pickup or SUV has a good path to Ground.

So, in this test step, you're gonna' verify that the MAP sensor is getting Ground using your multimeter once again.

NOTE: The fuel injection computer is the component that provides Ground to the MAP sensor. Be careful and don't short this wire to battery 12 Volts or you'll fry the computer. The multimeter voltage test suggested in the test instructions is a safe way to check for Ground in the wire.

Alright, this is what you'll need to do:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Turn the key on but don't crank or start the engine.

3. 3

   Probe the wire that connects to the terminal labeled with the number 3, in the illustration above, with the black multimeter test lead.

4. 4

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

5. 5

   Your multimeter should show 10 to 12 Volts DC.

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

CASE 1: The multimeter registered 10 to 12 Volts. This is the correct test result.

This test result also means that the MAP sensor, on your Isuzu pickup or SUV, is fried and needs to be replaced if you have:

• Confirmed that the MAP sensor voltage signal does not decrease/increase as you apply/release vacuum to it (TEST 1).
• Confirmed that the MAP sensor is receiving 5 Volts (TEST 2).
• Confirmed that the MAP sensor is receiving Ground (TEST 3).

CASE 2: The multimeter DID NOT register 10 to 12 Volts. Double check your multimeter connections and repeat the test. If your multimeter results still do not indicate 10 to 12 Volts, then the MAP sensor is not fried and not the cause of the MAP diagnostic trouble code (DTC) issue.

Here's why: Without a good path to Ground, that the PCM provides internally, the MAP sensor will not work. With this test result, you have eliminated the MAP sensor as bad.

The MAP Sensor Code Won't Go Away

So you tested the MAP sensor and your test results indicate it's good or you replaced it already but the MAP sensor trouble code keeps coming back. Well, here are a couple of suggestions that might inspire your next diagnostic move:

Engine mechanical condition is bad:

• Specifically, the engine has too low compression in one or several cylinders. This will cause the engine to idle rough and make the PCM think it's a bad MAP sensor. I suggest doing an engine compression test to find out.

The fuel pump is going out.

• It happens that the fuel pump, instead of just giving out outright, it'll start to send less than the ideal volume of fuel. This will lean out the air/fuel mixture to the point that the computer will think it's the MAP sensor going bad (among several things). This can be tested by doing a fuel pressure test and comparing the results to a repair manual's fuel pressure specifications.

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.