TEST 3: Verifying The MAP Sensor Ground Circuit
If you've reached this point, you now know two things:
1.) The MAP sensor is not producing a signal when you applied vacuum to it in TEST 1.
2.) That it is getting power, in the form of 5 Volts DC (TEST 2).
The next step (after verifying the MAP signal and power circuit) is to make sure that the MAP sensor on your Dodge pick up (or van or SUV) has a good path to Ground.
This is also a pretty easy test, in which you'll use your multimeter once again.
IMPORTANT: Since 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
With your multimeter still in Volts DC mode from the previous test and the key ON (but engine OFF).
- 2
Probe the wire labeled with the number 3 in the image above, with the black multimeter test lead.
It doesn't matter if you probe this circuit (wire) with the connector connected to the MAP sensor or not, but do not probe the front of the connector (if you decide to unplug the connector to test for this path to Ground). - 3
Now connect the red multimeter test lead on the battery's positive (+) post.
- 4
Your multimeter should show you either: 12 Volts or 0 Volts.
OK, let's take a look at what your results mean:
CASE 1: The multimeter registered 12 Volts. This means that the MAP sensor is being supplied with Ground (by the PCM). It also confirms that the MAP sensor is bad. Replace the MAP sensor.
Here's why: In MAP TEST 1 and 2, you verified that the MAP sensor is not producing the correct values (when you applied vacuum) and that it does have power. Since in this test step you have confirmed that the MAP sensor does have a solid path to Ground, these results, interpreted together, indicate that the MAP sensor is bad.
If you'd like to save a few bucks on the MAP sensor, check out the following section: Where To Buy The MAP Sensor And Save.
CASE 2: The multimeter DID NOT register 12 Volts. Double check your multimeter connections and repeat the test. If your multimeter results still do not indicate 12 Volts, then the reason the MAP sensor is not functioning (producing a signal) is due to this lack of Ground.
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:
- A major vacuum leak is leaning out the air/fuel mixture that's provoking a rough idle and fooling the PCM into thinking the MAP is at fault.
- The MAP sensor's rubber elbow (that connects it to the vacuum outlet nipple on the throttle body), has dry rot and/or is broken.
- 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 testing the fuel pump with a fuel pressure gauge and see if it's at specification.
Where To Buy The MAP Sensor And Save
You can buy the MAP sensor for your Dodge pickup (van, SUV) in just about any auto parts store but you'll spend a whole lot more because they mark it up quite a bit.
My suggestion is to buy it online or at least comparison shop to get an idea of how much it costs and how much you can save.
The following links:
Not sure if the above MAP sensor fits your particular Dodge or Jeep? Don't worry, once you get to the site, they'll make sure it fits by asking you the particulars of your vehicle. If it doesn't fit, they'll find you the right one.
Related Test Articles
As I mentioned at the beginning of the article, quite a few things can fool the fuel injection computer into thinking that the MAP sensor is bad (when it isn't). So the key to testing the manifold absolute pressure (MAP) sensor is to test it off of the engine (although it has to remain connected to its electrical connector to get power and Ground).
I've written several more tutorials that may be of interest to you that you can find in this index: Chrysler 3.9L, 5.2L, 5.9L Index Of Articles.
Here's a sample of the tutorials you'll find in the index:
- How To Test A No Start Condition (Dodge 3.9L, 5.2L, 5.9L).
- How To Test The Crank Sensor (1994-1996 3.9L, 5.2L, 5.9L Chrysler).
- How Can I Tell If My Automatic Transmission Needs An Overhaul?
- How To Test The MAP Sensor (P0107, P0108) (Dodge 3.9L, 5.2L, 5.9L).
- How To Diagnose Misfire Codes (Dodge 3.9L, 5.2L, 5.9L).
If this info saved the day, buy me a beer!
