In this tutorial, I'm gonna' show you the fastest and surest way to test the manifold absolute pressure (MAP) sensor on your 3.5L or 4.2L equipped GM pickup or SUV. Not only that, the MAP sensor test I'm gonna' show you doesn't require a scan tool (to test the manifold absolute pressure (aka MAP) sensor).
Now, in case you're wondering how we're gonna' test the MAP sensor.... I'll show you how to test it using a multimeter and a vacuum pump (and if you don't have a vacuum pump, you can just suck on the MAP sensor's nipple using a vacuum hose and the good ole' lungs).
This tutorial should also help you diagnose the following trouble codes: P0106, P0107, and P0108. Now, don't worry... this is a step-by-step test that will tell you whether you have a BAD MAP sensor or not on your hands.
Here are the main points of this tutorial:
The most obvious symptom, you'll see when the manifold absolute pressure (MAP) sensor fails, is the check engine light (CEL) shining nice and bright on your instrument cluster.
You'll also see one or several of the following symptoms:
Here's a basic list of tools you'll need:
The MAP sensor's job is to measure the pressure inside the intake manifold when the engine is running... another name for this pressure is vacuum.
Vacuum is created within the intake manifold as the pistons travel downward and draw air on their intake stroke.
The PCM (Powertrain Control Module = Fuel Injection Computer) will use the MAP sensor input, along with the inputs of the MAF sensor and throttle position sensor (TPS) to calculate fuel injection, ignition timing... among several things.
The MAP sensor needs three very important things to work and these are:
The way that we're gonna' test the MAP sensor is independent of engine vacuum. We'll supply our own vacuum with a vacuum pump. Why? Because a few different engine conditions/malfunctions can fool the PCM into thinking that the MAP sensor is BAD when it really isn't...
...So the surest way to make sure that the MAP sensor is OK or not, is to verify its signal with a vacuum pump and I'll show you how to do that in this tutorial.
The MAP sensor has 3 wires coming out of its connector.
Each wire (circuit) is identified by a letter on the connector itself (if you take a close look at the connector, you'll see the letters A, B, and C embossed on it).
Each wire (circuit) has a specific job to do and below are those job descriptions.
IMPORTANT: The color of the wires below are probably not gonna be the ones on your particular vehicle... and this is OK. Why? Because the circuit descriptions are all the same irrespective of the color of the wire.
|MAP Sensor Sensor Circuits|
|A||Orange w/ Black stripe||Ground (known as: Low Reference)|
|B||Light Green||MAP Sensor Signal|
|C||Grey||5 Volt Reference|
“A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.”