TEST 2: Making Sure The MAP Sensor Is Getting 5 Volts
If the MAP sensor did not pass TEST 1, then there's a good chance it's not receiving 5 Volts from the fuel injection computer.
In this test section, we'll make sure the wire labeled with the letter C is delivering 5 Volts DC to the MAP sensor.
If the MAP sensor is receiving 5 Volts, then we'll move on to the last test (TEST 3).
These are the test steps:
- 1
Place your multimeter still in Volts DC mode.
- 2
Disconnect the MAP sensor from its electrical connector.
- 3
Probe the wire labeled with the letter C, in the image viewer, with the red multimeter test lead.
NOTE: If you probe the front of the female terminal with your multimeter test lead, be careful not to damage it. - 4
Now Ground the black multimeter test lead on the battery's negative (-) post.
- 5
Turn the key ON but with the engine OFF.
- 6
Your multimeter should show you either:
1.) 4.5 to 5 Volts DC
2.) 0 Volts.
Let's take a look at what your results mean:
CASE 1: The multimeter registered 5 Volts. This is the correct and expected test result and it confirms that the MAP sensor is getting power.
The next test is to make sure that it's getting Ground. Go to: TEST 3: Making Sure The MAP Sensor Is Getting Ground.
CASE 2: The multimeter DID NOT register 5 Volts. Without 5 Volts, the MAP sensor will not function.
Although it's beyond the scope of this tutorial to troubleshoot the cause of these missing 5 Volts, you have now eliminated the MAP sensor itself as bad.
Resolving the issue that is keeping these 5 Volts from being supplied will solve the MAP sensor issue on your 3.1L V6 Chevrolet (Pontiac).
TEST 3: Making Sure The MAP Sensor Is Getting Ground
So far, the previous two tests have confirmed that:
- The MAP sensor's voltage signal does not decrease/increase as you apply/release vacuum to the sensor.
- The MAP sensor is receiving 5 Volts DC from the fuel injection computer.
In this last test section, we're going to make sure that the MAP sensor is receiving Ground from the wire labeled with the letter A.
IMPORTANT: Ground is supplied to the MAP sensor by the fuel injection computer internally. Be careful not to short this wire to battery 12 Volts since doing so will fry the computer. The multimeter voltage test suggested in the following instructions is a safe way to test for the presence of Ground in the wire.
Let's get testing:
- 1
Place your multimeter still in Volts DC mode.
- 2
Disconnect the MAP sensor from its electrical connector.
- 3
Probe the wire labeled with the letter A in the image above, with the black multimeter test lead.
NOTE: If you probe the front of the female terminal with your multimeter test lead, be careful not to damage it. - 4
Connect the red multimeter test lead on the battery's positive (+) post.
- 5
Turn the key ON but with the engine OFF.
- 6
Your multimeter should show you either:
1.) 10 to 12 Volts DC
2.) 0 Volts.
OK, let's take a look at what your results mean:
CASE 1: The multimeter registered 10 to 12 Volts. This is the correct and expected test result and it confirms that the MAP sensor is getting Ground.
You can conclude the MAP sensor is fried and needs to be replaced if you have:
- Confirmed that the MAP sensor's voltage signal does not decrease/increase as you apply/release vacuum to the sensor (TEST 1).
- Confirmed that the MAP sensor is receiving 5 Volts (TEST 2).
- Confirmed in this test section that the MAP sensor is receiving Ground.
If you'd like to buy the original AC Delco MAP sensor and save, take a look at the section: Where To Buy The MAP Sensor And Save.
CASE 2: The multimeter DID NOT register 10 to 12 Volts. This test result tells you that the MAP sensor is not receiving Ground. Without Ground the MAP sensor will not function.
With this test result you can eliminate the MAP sensor itself as bad. Your next step is to find out why this Ground is missing and resolve the problem.
Usually, this missing Ground is due to an open-circuit problem in the wire between the MAP sensor's connector and the fuel injection computer's connector.
MAP Sensor Code Won't Go Away
In some cases, no matter what you do or replace, the MAP sensor trouble code does not go away. In these cases, it's usually some other problem causing the MAP sensor to read and report a manifold vacuum reading that the fuel injection computer does not like.
If this is happening in your case, the following testing suggestions may help find the source of the problem:
- The MAP sensor's vacuum hose is leaking vacuum because it's cracked, or broken, or damaged. Visually inspect the vacuum hose or line and replace them if damaged in any way.
- The engine has several cylinders with very low engine compression causing it to idle rough and produce a low or erratic vacuum. I recommend doing a compression test. You can find the compression test procedure explained here:
- 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 problems is to slightly tap the MAP sensor with the handle of a screwdriver as I read its voltage signal output. If the tapping affects the voltage readings as I apply vacuum, then I can conclude that the MAP sensor is bad.
- The MAP sensor's connector is bad, usually the locking tab is broken and the connector has worked itself loose, causing an intermittent false connection.
- Your fuel pump is starting to go bad and is not sending enough fuel and/or fuel pressure to the fuel injectors. I suggest a fuel pump test.
More 3.1L V6 Chevrolet, Pontiac Tutorials
You can find a complete list of 3.1L V6 Chevrolet (Pontiac) tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test A Blown Head Gasket (3.1L V6 Chevrolet, Pontiac).
- How To Test The Engine Compression (3.1L V6 Chevrolet, Pontiac).
- How To Test The Fuel Pump (1995-1999 3.1L V6 Chevrolet Lumina, Monte Carlo).
- What Does The CKP Sensor Do? (3.1L V6 Chevrolet, Pontiac).
If this info saved the day, buy me a beer!
