TEST 2: Checking That The MAP Sensor Is Getting Power
In TEST 1 you confirmed that the MAP sensor is NOT creating a signal when you applied vacuum to its vacuum port.
So the next steps, before condemning it as bad, is to make sure that your Jeep's PCM is feeding it with power (5 Volts) and Ground.
These 5 Volts are fed to the MAP sensor thru' the wire that connects to sensor's harness connector terminal labeled with the number 3 in the illustration above.
NOTE: You can check for these 5 Volts with the MAP sensor connected or disconnected from its harness connector.
This is what you'll need to do:
- 1
Place your multimeter in Volts DC mode.
- 2
Disconnect the MAP sensor from its electrical connector.
- 3
With the red multimeter test lead probe the wire that connects to the terminal labeled with the number 3.
Avoid probing the front of the connector to avoid damaging the female metal terminal.
The best way to get to the signal inside the wire is using a wire piercing probe (to see what this tool looks like, click here: Wire-Piercing Probe). - 4
Connect the black multimeter test lead directly on the battery's negative (-) terminal.
- 5
Turn the key to the ON position (but don't start the engine).
- 6
Your multimeter should read 4.5 to 5 Volts DC.
Let's take a look at your test results:
CASE 1: 4.5 to 5 Volts are present. So far so good, since this means that the PCM is supplying power to the manifold absolute pressure (MAP) sensor.
The next step is to make sure that the PCM is feeding your Jeep's MAP sensor with Ground. For this test, go to: TEST 3: Verifying The MAP Sensor Is Getting Ground.
CASE 2: 4.5 to 5 Volts ARE NOT present. Recheck your multimeter connections and retest.
If after checking all of your multimeter connections and making sure the key is in the ON position AND your multimeter does not register the 4.5 to 5 Volts DC, then you've found the reason for the MAP sensor code/failure.
Without power in this circuit, the MAP sensor will not work. Now, it's beyond the scope of this article to test for this missing Voltage, but the most likely cause will be an ‘open’ or a short between the PCM connector and the MAP sensor connector.
TEST 3: Verifying The MAP Sensor Is Getting Ground
If you've reached this point, you've confirmed that:
One: The MAP sensor is NOT producing a Signal (TEST 1).
Two: That the MAP sensor is getting power in the form of 5 Volts (TEST 2).
The next step and the purpose of this test step, is to make sure that the MAP sensor is getting Ground on the wire that connects to the terminal labeled with the number 1 (in the image above).
IMPORTANT: The PCM is the one that provides this Ground internally, so be careful and don't intentionally or accidentally short this wire to battery voltage or you'll fry the PCM.
This is what you'll need to do:
- 1
Place your multimeter in Volts DC mode.
- 2
Disconnect the MAP sensor from its electrical connector.
- 3
With the black multimeter test lead probe the wire that connects to the terminal labeled with the number 1.
Avoid probing the front of the connector to avoid damaging the female metal terminal.
The best way to get to the signal inside the wire is using a wire piercing probe (to see what this tool looks like, click here: Wire-Piercing Probe). - 4
Connect the red multimeter test lead directly on the battery's positive (-) terminal.
- 5
Turn the key to the ON position (but don't start the engine).
- 6
Your multimeter should read 10 to 12 Volts DC.
Let's take a look at your test results:
CASE 1: Your multimeter showed 10 to 12 Volts. So far so good, since this means that the PCM is supplying Ground to the manifold absolute pressure (MAP) sensor.
This confirms that the manifold absolute pressure (MAP) sensor is bad and needs to be replaced. Why? Well, because so far you have confirmed that:
- The MAP sensor is not producing a decreasing voltage signal when vacuum is applied to it (TEST 1).
- The MAP sensor is getting its 5 Volts (TEST 2).
- In this test step, you've confirmed that the MAP sensor is getting Ground.
Taking all of these 3 test results, you can conclude with confidence that you need to replace the MAP sensor with a new one.
CASE 2: Your multimeter DID NOT show 10 to 12 Volts. Recheck your multimeter connections and retest.
If after checking all of your multimeter connections and making sure the key is in the ON position AND your multimeter does not register the 10 to 12 Volts DC, then you've found the reason for the MAP sensor code/failure.
Without Ground in this circuit, the MAP sensor will not work. Now, it's beyond the scope of this article to test for this missing Ground, but the most likely cause will be an ‘open’ between the PCM connector and the MAP sensor connector.
More 4.0L Jeep Diagnostic Test Tutorials
You can find a complete list of tutorials here: Index of Jeep 4.0L Articles.
Here's a sample of the tutorials you'll find in the index:
- How To Test The Starter Motor (Jeep 4.0L).
- Jeep PWM Fan Relay Test Troubleshooting An Overheating Condition.
- How To Troubleshoot A Bad Fuel Injector (Jeep 4.0L).
- How To Test For A Blown Head Gasket (Jeep 4.0L).
- How To Test Engine Compression (Jeep 4.0L).
If this info saved the day, buy me a beer!
