This accuse will assist you to check the manifold absolute pressure (MAP) sensor on the 2002-2007 4.2L Chevrolet TrailBlazer or GMC Envoy.

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All you"ll should test that is a vacuum pump and a multimeter. Currently if you don"t have a vacuum pump, don"t worry. I"ll show you exactly how to check it there is no one.

In a nutshell, I"ll show you how to test the MAP sensor signal and also how come make certain that the MAP sensor is gaining power and Ground.

friend can find this tutorial in Spanish here: Cómo Probar El Sensor MAP (2002-2007 4.2L Chevrolet Trailblazer) (at: autotecnico-online.com).

Symptoms the A negative MAP Sensor

The fuel injection system on her 4.2L Chevrolet TrailBlazer or GMC Envoy is a ‘speed density’ form fuel system.

In this kind of fuel system, the fuel injection computer system needs to understand three points to discover out how much wait is entering her Chevy TrailBlazer or GMC Envoy"s engine and inject the exactly amount that fuel into its 6 cylinders.

These 3 points are: The temperature the the air entering the engine, the engine RPM, and the pack that the engine is under.

The MAP sensor is the one that provides the engine load information so that the computer system can inject the exactly amount the fuel for the quantity of air entering the engine.

Since the MAP sensor is a critical component of the engine monitoring system, when this bad boy fails you"re gonna" watch one or more of the complying with symptoms:

Check engine irradiate (CEL) is glowing nice and bright ~ above the tool cluster.DTC P0107 MAP sensor Circuit low Voltage.DTC P0108 MAP sensor Circuit High Voltage.Rough idle.‘Rotten egg’ odor coming from the exhaust.Won"t happen the state mandated emissions test.Bad gas mileage.Lack that power, stormy idle, or hesitation.Engine cranks a lengthy time prior to starting.

The MAP sensor is a 3 wire form sensor. This way that it has actually a strength wire, a ground wire and a signal wire. The table listed below has a brief description that each:

CGRY5 Volts

Where to Buy The MAP Sensor and also Save

If your test results indicate that the MAP sensor is defective on her Chevrolet TrailBlazer or GMC Envoy climate you should that take it a look in ~ the complying with links and also comparison shop. I think you"ll save a couple of bucks by purchase it digital (my local auto parts store sell the AC-Delco MAP sensor for $113!! You can buy it online for around $35! -see attach below).

NOTE: Not certain if the MAP sensor in the links above fits her 4.2L Chevrolet TrailBlazer or GMC Envoy? Don"t worry, once you gain to the website they will make certain that fits by questioning you because that the specifics of your vehicle. If it doesn"t fit, they"ll find you the ideal one.

TEST 1: trial and error The MAP Sensor Voltage Signal

The very very first thing the we"re walking to do is to check the MAP sensor"s signal with a multimeter together we use vacuum come it.

We"re no going to start the engine due to the fact that we"re no going to usage engine manifold vacuum to check the MAP sensor. What will carry out is connect a vacuum pump come it so that we have the right to manually use a vacuum come the MAP sensor.

Now if friend don"t have actually a vacuum pump there"s no need to worry. Because you deserve to use your mouth to apply vacuum to the MAP sensor via a vacuum hose.

If the MAP sensor on your 4.2L Chevrolet TrailBlazer or GMC Envoy is defective, you"ll check out that the MAP sensor signal will not decrease as you apply vacuum come it.

To be a bit much more specific, the MAP sensor voltage signal will stay stuck in one value no matter just how much vacuum you apply to it.

IMPORTANT: The MAP sensor must remain connected to its electrical connector because that this check to work. You"ll have to use a back-probe or a wire piercing probe to accessibility the voltage inside the wire. You have the right to see an example of this device here: Wire Piercing Probe.

Let"s obtain started:


Remove the MAP sensor indigenous the entry manifold.


Connect her vacuum pump come the MAP sensor"s vacuum inlet port. Reconnect the MAP sensor come its connector if girlfriend disconnected it.


Set her multimeter"s selector to Volts DC mode and also with the red test lead, probe the LT GRN cable of the MAP sensor"s connector. This wire is identified by the letter B in the photograph above.Remember, the MAP sensor need to remain associated to that 3 cable connector.


Ground the black multimeter check lead straight on the battery an unfavorable (-) terminal.


Turn the key on however don"t start the engine. This will certainly power up the MAP sensor and you must see a reading of 4.7 Volts DC on your multimeter.


Now, apply vacuum to the MAP sensor v the vacuum pump (or her mouth). The voltage signal value have to decrease.If you"re utilizing a vacuum pump: in ~ 5 in.Hg → 3.9 Volts. In ~ 10 in.Hg → 3 Volts. At 15 in.Hg → 2.1 Volts. At 20 in.Hg → 1.2 Volts.


Release the vacuum. Once released, her multimeter should show the original voltage value.Repeat this check step numerous times making sure that every time the voltage decreases/increases as you apply/release vacuum.

Let"s take it a look in ~ what her test results mean:

CASE 1: The MAP voltage signal decreased and also increased as you applied and also released vacuum. This is the exactly test an outcome and allows you understand that the MAP sensor is performing beautifully (it"s not defective).

You can additionally conclude that the MAP sensor is acquiring power (5 Volts) and Ground too.

CASE 2: The MAP voltage signal DID no decrease/increase together you applied and also released vacuum. There"s a good chance the MAP sensor is defective or it"s not gaining power or it"s not getting Ground.

So, to make certain the MAP sensor is defective the next step is make sure it"s getting 5 Volts and Ground. Go to: test 2: Verifying MAP Sensor has actually 5 Volts and Ground.

CASE 3: The multimeter DID no register any kind of voltage. There"s a great chance the MAP sensor is defective or it"s not obtaining power or it"s not acquiring Ground.

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To uncover out the following step is make certain the MAP sensor is obtaining 5 Volts and also Ground. Walk to: test 2: Verifying MAP Sensor has 5 Volts and also Ground.