How To Test a Chevy Blazer MAP Sensor

How To Test a Chevy Blazer MAP Sensor


Your Chevy Blazer utilizes either a Throttle Body Injection or Central Port Injection EFI system, depending on the year. The Chevy Blazer MAP sensor is a three pin unit that communicates the intake manifold pressure to your Powertrain Control Module.

This sensor is required for your engine to properly operate, and when your MAP sensor begins to fail your check engine light will turn on. When you need to learn how to test your Chevy Blazer MAP sensor, this How To DIY guide can get the job done.

Today I’ll be showing you how to test a Blazer MAP Sensor in a 2003 Chevy truck with a 4.3 liter engine in it.

chevy blazer map sensor

This sensor is connected to your intake manifold, and is sealed by the orange rubber grommet shown above. You will be using a multimeter to read the voltages at this MAP sensor to determine whether or not it’s any good. Need a quick primer on how to use a multimeter? Check it out here.

How To Check your Blazer MAP Sensor for Power

Testing your Blazer MAP Sensor is broken up into different segments. We will begin by testing the sensor for power and ground signals. To begin you’ll need to turn your Chevy Blazer ignition to the “ON” position or POSITION II.

Next open your hood and locate the MAP sensor, which is mounted to your plastic manifold plenum. It’s connected to a three pin weatherproof connector, and I’ll be showing you which wires you need to check shortly.

how to test a Blazer MAP Sensor

Once you’ve located your Blazer MAP sensor, you will need to unplug the three pin connector. The wire you will need to check is labeled on PIN A, which is the first wire on the left hand side when facing the sensor. If you have unplugged the harness and are looking at the harness side, this is the right most pin on the connector.

Use the Blazer MAP sensor wiring diagram below to check for the pinouts in question. Place your black multimeter lead to the negative side of your battery, and then gently probe PIN A of your wiring harness.

how to test a Blazer MAP Sensor 3

You should see 5 volts of DC power at this wire. This means that your PCM is sending the right voltage to power the operation of your Blazer MAP sensor. The next wire you need to check is PIN C, and you will be checking for the low reference ground signal here.

Once you have determined that your manifold pressure sensor is receiving power and ground, the last thing to do is check your MAP signal wire. This step can be skipped if you have an OBDII trouble code indicating that your MAP signal is too high or too low. Because you’ve already tested your power and ground signals, go ahead and replace your Blazer pressure sensor now.

Testing your Blazer MAP Sensor for Signal

This part of our How To DIY test requires the use of a backpin at terminal B or the middle wire. You can insert one or simply elect to pierce the middle wire with your multimeter probe. Because the pressure sensor in your Chevy will lower the signal voltage as more vacuum is applied, you can test this with the engine off and the key at the ON position now.

Reconnect your Blazer pressure sensor and read the signal voltage at the middle wire. With absolutely nothing going on, you should have between  4.6 – 4.8 Volts. This signal voltage represents 0 in. Hg worth of vacuum at your intake manifold.

Now turn on your engine and allow it to idle. Keep clear of your engine and any moving components. This includes your belts, pulleys and especially your cooling fans. Measure the voltage signal at idle, and it should vary between 3.5 – 3.9 Volts. This represents up to 5 in. Hg worth of vacuum at the intake.

You can increase your engine speed to vary the vacuum but without a true vacuum tester you won’t have a true control set of data or a way to test it. To truly test for your Blazer MAP sensor signal, you must remove the sensor and use a automotive vacuum pump to test the operation.

You can buy one of these at your local auto store or even rent one with a deposit. These are also known as Mighty Vac pumps, and allow you to set a vacuum or pressure through a hose. Here’s the chart of pressure that your 5 volt Chevy MAP sensor is supposed to read.

  • 0 in. Hg =  4.7 Volts.
  • 5 in. Hg = 3.9 Volts.
  • 10 in. Hg = 3.0 Volts.
  • 20 in. Hg = 1.1 Volts.

If your Blazer MAP sensor does not return these values at the vacuum levels specified, it has gone bad. Replace your pressure sensor and use a OBDII scan tool to clear your trouble code. You now know how to test a Chevy Blazer MAP Sensor. Have any questions about this guide? Leave them for us below and let us know!