The 300M MAP sensor in your Chrysler is an important part of your EFI system. It’s also known as the Manifold Absolute Pressure Sensor, the simply the pressure sensor. It’s mounted into the intake system, and it measures the amount of air that’s entering the engine. Based on the signal from your 300M MAP sensor, the engine computer will control your fuel injectors.
When you turn on your Chrysler 300M, the air rushing into the engine creates a vacuum. This pressure is registered by your 300M MAP sensor. The primary role of this sensor is to translate the pressure into a voltage signal that your Powertrain Control Module can understand. When the 300M MAP sensor in your Chrysler sedan starts to fail or goes bad, one of the earliest warning signs is a 300M check engine light.
Today I’ll be showing you how to test the 300M MAP Sensor in a 1999 Chrysler with a 3.5 liter engine. The 300M MAP Sensor is a four wire unit that can be easily tested using a digital multimeter. The important thing to remember is as the engine vacuum increases, your MAP signal voltage decreases. And of course as the engine vacuum decreases, the MAP signal voltage will then increase.
Before you begin our How To guide to testing your 300M MAP Sensor, there’s a few common 300 symptoms that can arise from a bad pressure sensor. As we’ve already discussed the 300M check engine light is one of the first signs of trouble. When you see your 300 check engine light turn on, you’ll need a OBDII scan tool to check the stored DTC code.
Symptoms of a failed 300M MAP Sensor
Although the Chrysler service light is one of the early warning signs, there are a few other 300M issues that can strike. Here’s a look at some of the 300M problems you’ll see when the pressure sensor goes south.
- 300M won’t start
- Bad engine idle
- Poor fuel economy
- Surging idle
- CHECK ENGINE LIGHT ON
To begin testing your 300M MAP sensor, you’ll need to insert your ignition key and turn to the “ON” position.
Testing your 300M MAP Sensor
Unlike some of the other Chrysler models in this year range with a 3 pin MAP sensor, the 300M MAP sensor is slightly harder to test. The fourth wire is an extra ground circuit in your 300M MAP wiring diagram. You’ll be using your digital multimeter and referring to the 300M MAP Sensor wiring schematic below.
We’ll be starting with the aforementioned ground circuits at the 300M MAP sensor. To test the ground wires, you’ll need to turn the dial of your multimeter to read voltage. If you aren’t sure what a multimeter is or how to use one, check our primer here. Begin by disconnecting the 300M MAP wiring connector.
Now you can proceed by putting the multimeter red lead or positive lead on the battery. Put the black lead to the wire labeled A in the 300M MAP wiring diagram above. This is the chassis ground for your Chrysler manifold pressure sensor. Once you’ve tested this wire, the next wire to check is PIN B, which is another engine ground or the internal one supplied by the Powertrain Control Module.
Once you’ve confirmed the ground at the 300M MAP sensor, the next wire to check is the power. The power wire is the one that leads to terminal C on the wiring diagram. Make sure that your engine ignition is turned to the ON position.
Testing your 300M MAP sensor signal wire
The last leg of the testing procedure is to measure the signal that’s being transmitted from the sensor. In order to do this you need to plug the MAP sensor back in. With the manifold absolute pressure sensor plugged back in, you’ll be testing the signal at PIN D.
With your engine off and the ignition turned to the ON position, the MAP signal should read 4.5 volts. If you have this signal, you will need to check the voltage while the engine is running. Before you do this you will need to peel back the wiring that leads to PIN D, but do it further away from the front of the engine or pulleys. Make sure the wire is exposed so that you can test safely.
Start the engine and allow it to idle. Make sure that the engine bay is clear of tools before you start the engine. Before you measure the voltage make sure that you stay clear of the cooling fans or drive belts. Measure the voltage at the wire as the engine is running. Increase the engine speed and read the voltage, as it should slowly decrease as the engine vacuum increases.
If your 300M MAP sensor does not respond properly, it’s time for a replacement unit. Have any questions about this guide to your 300 manifold pressure sensor? Leave us a comment below and let us know!
