MAP SENSOR TEST 2: Making Sure The MAP Sensor Is Getting 5 Volts
So far, in MAP TEST 1, you have verified that the MAP sensor on your GM 2.8L, 3.1L, or 3.4L car or mini-van is not creating a signal or the signal is erratic.
An so, in this MAP sensor test step, you're gonna' verify that the MAP sensor is getting power, since without power it won't work. This power come in the form of 5 Volts and the PCM (Powertrain Control Module = Fuel Injection Computer) is the one that provides this juice.
Since this circuit is directly connected to the PCM, be careful and don't short this wire to battery power (12 Volts), or you run the risk of frying the PCM.
Alright, this is what you'll need to do:
- 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 number 1, in the image above, with the red multimeter test lead.
- 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.
OK, now that the testing part is done, let's take a look at what your results mean:
CASE 1: The multimeter registered 5 Volts. This is the correct result and it's starting to look like the MAP sensor is bad but you still need to check that the MAP sensor is getting Ground. For the Ground test, go to: MAP SENSOR TEST 3: Making Sure The MAP Sensor Is Getting Ground.
CASE 2: The multimeter DID NOT register 5 Volts. This results lets you know that the MAP sensor is not bad, since without these 5 Volts DC, the MAP sensor can not function.
Although it's beyond the scope of this article to troubleshoot the cause of these missing 5 Volts, you have now eliminated the MAP sensor as bad. Resolving the issue that is keeping these 5 Volts from being supplied will solve the MAP sensor issue on your GM 2.8L, 3.1L, or 3.4L car or mini-van.
MAP SENSOR TEST 3: Making Sure The MAP Sensor Is Getting Ground
The next step (after verifying the MAP signal and power circuit) is to make sure that the MAP sensor on your GM 2.8L, 3.1L, or 3.4L car or mini-van has a good path to Ground. So, in this test step, you're gonna' verify that the MAP sensor is getting Ground using your multimeter once again.
IMPORTANT: This circuit is directly connected to the PCM, be very careful and don't short this wire to battery power (12 Volts), or you WILL FRY the PCM.
Alright, this is what you'll need to do:
- 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 number 3 in the image above, with the black multimeter test lead.
- 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 normal result and it means that the MAP sensor your GM 2.8L, 3.1L, or 3.4L car or mini-van is getting Ground from the fuel injection computer.
You can conclude the MAP sensor is fried and needs to be replaced if you have:
- Confirmed that the MAP sensor is not producing the correct values (when you applied vacuum) in TEST 1.
- Confirmed that it does have power in TEST 2.
- Confirmed in this test section that it does have 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. Double check your multimeter connections and repeat the test. If your multimeter results still do not indicate 12 Volts, then the MAP is not fried and not the cause of the MAP diagnostic trouble code (DTC) issue.
Here's why: Without a good path to Ground, that the PCM provides internally, the MAP sensor will not work. With this test result, you have eliminated the MAP sensor as bad.
MAP Sensor Code Won't Go Away
So you've tested the MAP sensor and according to the test results, it's good. But the check engine light keeps coming back on even after you erased the diagnostic trouble code (DTC) from the computer's (PCM) memory. Well, here are a couple of suggestions that might inspire your next diagnostic move:
- The MAP sensor's O-rings, the ones located on the vacuum inlet nipple are missing or are too old and they're not sealing properly. Visually check the O-rings and replace if necessary.
- The engine has several cylinders with very low engine compression causing it to idle rough and thus producing low or erratic vacuum. For this I suggest a compression test.
- 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 screw-driver and see if this tapping screws up the voltage readings as I apply vacuum.
- 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 up to the fuel injectors. I suggest a fuel pump test.
More 3.1L, 3.4L GM Tutorials
I've written several more tutorials that may be of interest to you. These are specific GM 2.8L, 3.1L, or 3.4L car or mini-van that you can find here: GM 3.1L, 3.4L Index Of Articles.
- How To Test The Blower Motor (GM 3.1L, 3.4L).
- How To Troubleshoot A No Start (GM 3.1L, 3.4L).
- Coolant Leaking From Intake Gaskets (GM 3.1L, 3.4L).
- How To Do An Engine Compression Test GM 3.1L, 3.4L.
- How To Test The Fuel Pump No Start Tests (GM 3.1L, 3.4L).
- Troubleshooting A Hard To Diagnose Misfire Case Study (GM 3.1L, 3.4L).
- How To Test The Ignition Coil Packs (GM 3.1L, 3.4L) (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!
