3-Wire MAP Sensor Diagnostic Test Chrysler, Dodge, Plymouth

MAP Sensor Code Won't Go Away

Nothing is more frustrating than replacing the MAP sensor (and erasing the trouble code) and then having the MAP sensor code come back during your road test.

Why does it happen? Usually because the MAP sensor is just reporting the effect that a problematic mechanical condition is having on the engine's ability to create vacuum inside the intake manifold.

Here are a few suggestions on what to check (if this is what's happening in your specific situation):

• There's a good chance that the o-ring on the MAP sensor's vacuum inlet nipple (the part that goes into the intake manifold to sense the vacuum) is torn, missing or distorted. When this happens, ambient air will leak into the intake manifold and skew the MAP sensor's readings.
• One of the most common things I've seen, is a rough idle caused by internal piston/valve wear that causes very low compression in one or several cylinders. This severe wear and tear will cause the engine to produce erratic and low vacuum readings and the PCM will accuse the MAP sensor as having failed. To check this, I suggest an engine compression test: How To Test The Engine Compression (Chrysler 2.0L, 2.4L) (at: troubleshootmyvehicle.com).
• The MAP sensor is failing intermittently. Which means that it works fine most of the time, but every now and then it doesn't:
  • I have found that the best way to test these intermittent failures is to slightly tap the MAP sensor with the handle of a screw-driver and see if this tapping screws up the voltage readings as I apply vacuum.
• Intermittent electrical short due to a broken MAP sensor connector. This usually happens when the MAP sensor's electrical connector's locking tab has broken.
• The second most common cause of a MAP sensor code is a Lean condition caused by a failing fuel pump. Most of the time a fuel pump will just fail and the vehicle doesn't start anymore, but not always. The fuel pump can slowly fail and not send enough fuel to keep the engine humming along nicely. To check for this, I recommend a fuel pressure test.

How The MAP Sensor Works

The manifold absolute pressure (MAP) sensor's job is to measure the amount of vacuum that is created by the downward stroke of the engine pistons and is one of the most important inputs the PCM needs to make you car or mini-van run optimally.

So here, in a nutshell, is how the MAP sensor works when you crank and start your Chrysler (Dodge, Eagle, Plymouth) car or mini-van:

1. The PCM (Powertrain Control Module = Fuel Injection Computer) feeds the MAP sensor with 5 Volts and Ground.
2. At idle (which means the throttle is closed) the MAP senses the amount of vacuum inside the intake manifold and sends the PCM (Powertrain Control Module = Fuel Injection Computer) a DC voltage signal of about 1.1 to 1.8 Volts at idle.
3. When you step on the accelerator pedal to accelerate the engine, vacuum immediately increases which causes the MAP signal voltage to the PCM to decrease.
4. With this decreasing voltage signal, the PCM knows it's time to inject more fuel, advance ignition timing, and a host of other things it has to do to keep your Chrysler (Dodge, Eagle, Plymouth) car or mini-van running optimally.
5. As you let go off the accelerator pedal to slow down, the throttle plate closes and of course the MAP sensor sends the info to the PCM as it returns to its idle voltage signal, till the whole cycle begins again.

Pretty easy stuff? The cool thing is that the tests to check out the MAP sensor's performance are as easy too.