TEST 2: Verifying The MAP Sensor Is Getting Power And Ground
In this test section, we're gonna' make sure that the MAP sensor is being fed with power and Ground. The two wires we'll test are:
- The orange ORG wire. This is the one that feeds 5 Volts DC to the manifold absolute pressure (MAP) sensor.
- The black w/ light blue stripe BLK/LT BLU wire. This is the one that feeds Ground to the manifold absolute pressure (MAP) sensor.
With your multimeter in Volts DC mode, this is what you need to do:
Verify that the ORG wire has voltage ( 4.5 to 5 Volts DC ) with the key on but engine off..
Connect the red multimeter test lead (using the appropriate tool) to ORG wire. Connect the black multimeter test lead to the negative battery terminal.
Your multimeter should read 4.5 to 5 Volts DC.
Verify that the BLK/LT BLU wire has Ground with the key on but engine off..
Connect the black multimeter test lead (using the appropriate tool) to BLK/LT BLU wire. Connect the red multimeter test lead to the positive battery terminal.
Your multimeter should read 12 Volts DC.
Let's take a look at what your test results mean:
CASE 1: The multimeter confirms that the MAP sensor has power and Ground. This is the correct and expected test result.
You can conclude that the MAP sensor is bad only if all tests have confirmed that:
- The MAP sensor is not providing a varying voltage signal when manually applying/releasing vacuum (to it).
- The MAP sensor is being fed 5 Volts DC.
- The MAP sensor is being fed ground.
Replacing the MAP sensor, if you've gotten all of the test results above, will solve the MAP sensor problem and/or trouble code.
CASE 2: Multimeter confirms that power or Ground are NOT reaching the MAP sensor. Double check that you're testing the correct MAP sensor harness terminal wires and repeat the test. If your multimeter still doesn't show the indicated voltages...
...then we can conclude that there's an open in the wire between the MAP sensor harness connector and the PCM's harness connector. In the extreme of cases, the PCM has an internal problem (although this is very rare).
Although testing these two conditions are beyond the scope of this article, you have now eliminated the MAP sensor as being the cause of the problem and/or the MAP sensor diagnostic trouble code (DTC) lighting up the check engine light (CEL).
MAP Sensor Code Won't Go Away
Over the years I've learned that quite a few conditions can cause the PCM to think the MAP sensor is bad when it isn't.
Below, I've highlighted the two most common problems I've run across that have caused a MAP sensor code (when the MAP sensor was good):
- Low engine compression condition:
- You can check this by doing an engine compression test.
- Low fuel pump pressure condition:
- Check fuel pump pressure with a fuel pressure gauge. A failing fuel pump will cause a lean air fuel mixture that can set a MAP sensor trouble code.
- The fuel injection computer is bad (internal short). Although this problem is not very common, it does happen.
- Check the MAP sensor's connector for damage. The most common problem with the connector is the locking tab has broken. This causes the connector to work itself loose, causing an intermittent false connection.
Before you jump the gun and start replacing the above... test the components first. This will help you save time, money, and the frustration of replacing parts your 4.7L Jeep Grand Cherokee does not need.
Where To Buy The MAP Sensor And Save
You can find the MAP sensor just about in anywhere. The best place to buy it and save a few bucks is is online.
The following links will help you comparison shop for the MAP sensor:
Not sure if the MAP sensor fits your particular vehicle? Don't worry, once you get to the site they'll make sure it fits by asking you the specifics of your particular GM vehicle. If it doesn't fit, they'll find you the right MAP sensor.