TEST 3: Verifying The MAP Sensor Has Ground
So far, you've confirmed that the MAP sensor has power (5 Volts DC)...
...In this test step, you're gonna' verify that the MAP sensor is getting Ground using your multimeter once again.
A word of caution: This Ground is provided directly by the PCM, so be very careful and don't short this wire to battery power (12 Volts), or you WILL FRY the PCM.
NOTE: You can perform this test with the MAP sensor connected to its connector or not.
Alright, this is what you'll need to do:
With your multimeter still in Volts DC mode from the previous test and the Key On (but engine off).
Probe the middle wire of the MAP sensor connector with the black multimeter test lead.
This is the wire that connects to the pin labeled with the number 2 of the MAP sensor, (see photo in the image viewer).
Connect the multimeter's red test lead to the battery's positive (+) post.
Your multimeter should show 12 Volts DC.
OK, let's take a look at what your results mean:
CASE 1: The multimeter registered 12 Volts. This is the normal and correct test result and lets you know that the PCM is providing a good path to Ground for the MAP sensor.
The next step, and the last one, is see if the MAP sensor can react to the changes in air pressure while you apply (and release) vacuum to it. For this test go to: TEST 4: Bench Testing The MAP sensor.
CASE 2: The multimeter DID NOT register 12 Volts. Double check your multimeter connections and repeat the test. If your multimeter results still do not indicate 12 Volts, then the MAP 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.
TEST 4: Bench Testing The MAP Sensor
Now that you've confirmed that the MAP sensor is getting both power and Ground... the last thing we need to do is bench test it.
Bench testing the MAP sensor will let us know beyond a shadow of a doubt if the MAP sensor is bad or not.
In a nutshell, we're gonna' remove the MAP sensor from the intake manifold, connect the multimeter to it, then manually apply vacuum to the MAP sensor (while it's still connected to its connector) and see if the MAP sensor's output voltage changes.
If you don't have a multimeter or need to upgrade yours, check out my recommendation here: Abe's multimeter Recommendation (at: easyautodiagnostics.com).
I'll show you how. This is what you'll need to do:
Remove the MAP sensor from the top of the intake manifold.
Reconnect the MAP sensor to its electrical connector, if you had to unplug it to remove it, since this test requires that the MAP sensor stay connected to its 3-wire electrical connector.
Connect your multimeter's red test lead to the wire that connects pin number 3 of the MAP sensor (see photo 2 of 2 in the image viewer).
You'll need to back-probe the MAP sensor connector or use a wire piercing probe to connect your multimeter to this circuit (to see what a wire piercing probe looks like, click here: Wire Piercing Probe).
Ground the black multimeter test lead.
I suggest grounding the black multimeter test lead directly on the battery negative (-) terminal.
Turn the key on (but don't start the engine) and take a look at what voltage your multimeter is registering.
It should register around 2.9 Volts (± 1 V). If your multimeter is registering something different at this point, don't panic because right now you're just setting up the test.
Attach a vacuum pump to the MAP sensor's vacuum inlet nipple using the appropriate size vacuum hose.
If you don't have a vacuum pump, you can use the ‘good ole' lungs’ and provide the necessary with your mouth.
The voltage, your multimeter is registering, should decrease as you apply vacuum with your vacuum pump (or with your mouth).
The MAP sensor's voltage, as registered on your multimeter, should increase back to the original voltage value you saw in step 4 as you release the vacuum you applied with the vacuum pump (or your mouth).
NOTE: Applying vacuum should make the MAP signal voltage get smaller. Releasing vacuum should make the MAP signal voltage get bigger (back to the original voltage you saw at the beginning of this test).
Let's take a look at what your test results mean:
CASE 1: The MAP sensor's voltage decreased and increased as you applied and released vacuum. This confirms that the MAP sensor is good and operating normally.
This test result completely eliminates the MAP sensor on your Honda as bad. If you're still having the MAP sensor trouble code come back, take a look at: MAP Sensor Is Good But Code Doesn't Go Away!.
CASE 2: The MAP sensor's voltage DID NOT decrease or increase as you applied and released vacuum. This confirms that the MAP sensor is bad and needs to be replaced.
If you need to buy the MAP sensor and would like to save some bucks, take a look at the section: Where To Buy The MAP Sensor.