TEST 3: Verifying The Ground Circuit
So far, your MAP sensor diagnostic has confirmed 3 things:
One: The MAP sensor is not producing a decreasing/increasing MAP voltage signal as you apply/release vacuum to it.
Two: The MAP sensor is getting fed with power (in the form of 5 Volts DC).
The next step, and the last one, to confirm that it's bad is to make sure it's getting Ground.
A word of caution: 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:
With your multimeter still in Volts DC mode from the previous test and the Key On (but Engine Off).
Probe the wire labeled with the number 2 in the image viewer, 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).
Now connect the red multimeter test lead on the battery's positive (+) post.
Your multimeter should register 10 to 12 Volts DC if Ground is present in the wire.
OK, let's take a look at what your results mean:
CASE 1: The multimeter registered 12 Volts. This is the normal result and it means that the MAP sensor your 3.3L Chrysler or Dodge mini-van is fried and needs to be replaced.
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.
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 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
Quite a few things can fool the PCM, on your Chrysler/Dodge mini-van, into thinking that the MAP sensor is bad when it isn't.
If you have already tested and/or replaced the MAP sensor but the trouble code keeps coming back (after erasing it and road testing the mini-van), then these suggestions might inspire your next diagnostic move:
- The MAP sensor's O-rings, the ones located on the vacuum port 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.
- The EGR valve is stuck open (on EGR valve equipped vehicles).
More 3.3L Chrysler, Dodge, And Plymouth Mini-Van Tutorials
You can find a complete list of tutorials in this index: Chrysler 3.3L Index Of Articles.
- How To Test The MAP Sensor (2001-2004 3.3L V6 Chrysler And Dodge Mini-Van).
- How To Test The Alternator (2001-2007 3.3L Chrysler).
- How To Test Engine Compression (1991-2007 3.3L V6 Chrysler, Dodge, Plymouth Mini-Van).
- How To Test The Coil Pack 3.3L, 3.8L Chrysler, Dodge, Plymouth (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!