MAP sensor
MAP sensor or Manifold Absolute Pressure sensor takes the pressure or vacuum in the intake manifold and converts it to an electrical signal for the PCM (Powertrain Control Module) to read. The PCM then knows how much fuel to send to the injectors and how much timing the engine needs.
At the bottom of the page is a YouTube video demonstrating how to test the sensor.
MAP sensor
Where is the MAP Sensor located?
On the YJ Wranglers just look on the firewall just above the valve cover. It’s a small black or grey box with vacuum line going to it and a plug with 3 wires.
Will it trigger the check engine light if the sensor is faulty?
In most cases, yes it will trigger the DTC light. But, if it’s only a little out of voltage range, it may not. If your Jeep is running bad, run the DTC sequence to get the PCM to read the stored codes out to you. Click here to learn how to run the diagnostic sequence.
Why does it fail?
Heat and vibration from being under the hood can eventually take its toll on the busy little sensor.
How do you test a MAP sensor to see if it’s bad?
To start out with you will need a couple tools. Nothing terribly expensive, just a decent multi-meter, a hand held vacuum pump and possibly a small paper clip.
- Test to make sure you have input voltage first. You do this by turning the key to the “On/Run” position.
- Put the black lead of your multi-meter to the Negative (-) side of your battery.
- Set you meter to test DC voltage. With the red lead probe the wire closest to the vacuum line (passenger side wire). There should be ~5 volts coming from that wire. If not, there is an issue with the wiring or the PCM. If you have voltage, then we are good for this step.
- Next lets test to see if there is voltage coming from the middle wire. This is the wire that sends voltage to the PCM telling it how much load is on the engine. You may not get exactly what you got from the first wire, but it will be close to 5 volts. If you are getting close to 5 volts that also means that the 3rd (the one on driver side) wire being the ground wire is functioning fine.
- No voltage? If you are not getting any voltage out of that middle wire you either have a bad MAP or a bad ground going to the sensor.
- Test the ground wire next. Leaving the black lead on the Negative (-) battery post, change the setting on your multi-meter to test ohms it may have a symbol like this “Ω”. If you have solid ground you should get a reading close to 0.00 Ω. If the meter settings don’t change from not touching to probing the wire, the wire isn’t grounded as it should be. Time to chase that wire to find the issue.
- Now lets say voltage and ground is good all across all 3 wires. Lets test the voltage sweep.
- Put the meter to test DC voltage and probe the middle wire. Again you should see close to 5 volts.
- Pull the engine vacuum line off the sensor and hook up the vacuum pump. Watching the voltage reading, slowly apply vacuum a little at a time.
- First apply 5 inches of vacuum, note the voltage reading. Now apply 10 inches of vacuum, note the voltage. Then 15 inches, note the voltage. There should be a steady transition throughout the voltage sweep.
- If the voltage is jumpy, spikes or voltage drops erratically through the transition of applying the vacuum. You have a bad MAP sensor and it's time to replace it.
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