How To Test The MAP Sensor (1991-1995 3.3L V6 Chrysler And Dodge Mini-Van)

TEST 3: Making Sure The MAP Sensor Is Getting Ground

Up to this point, your MAP sensor diagnostic has confirmed two key things:

• First: The MAP sensor isn't generating a proper voltage drop or increase when you apply or release vacuum.
• Second: The sensor is getting a solid 5 Volts of power from the PCM.

The final step to fully confirm the sensor's toast is checking if it's getting Ground. Without a proper Ground connection, it can't work.

IMPORTANT: This wire runs straight to the PCM (it provides this Ground internally), so do NOT short it to battery power (12 Volts), or you'll fry the PCM. The test I'm outlining below is a safe way to check for Ground in this circuit.

Here's how to do it:

1. 1

   Unplug the MAP sensor from its 3-wire connector.

2. 2

   Connect the red lead of your multimeter to the battery's positive (+) post.

3. 3

   Set your multimeter to Volts DC mode.

4. 4

   Turn the key to the ON position, but don't start the engine.

5. 5

   Use the black test lead to probe the front of the female terminal marked number 1 (see the illustration above of the connector).

6. 6

   Your meter should read somewhere between 10 and 12 Volts DC.

Let's break down what those results tell you:

CASE 1: Your multimeter showed 10 to 12 Volts. That's the result you're looking for.

You can conclude the sensor itself is bad and needs to be replaced, if you have:

• Confirmed the MAP sensor isn't generating a proper voltage drop or increase when you apply or release vacuum (TEST 1).
• Confirmed the sensor is getting a solid 5 Volts of power from the PCM (TEST 2).
• Confirmed it also has a good Ground path (this test section).

CASE 2: You didn't see 10 to 12 Volts on the multimeter. Double-check your test connections.

If you still don't see the 10 to 12 Volts, the MAP sensor isn't the problem —because it can't work at all without a Ground supply.

Troubleshooting the issue behind this missing Ground is beyond the scope of this tutorial, but at least you've ruled out the MAP sensor itself.

Once you fix the issue that's keeping the sensor from getting Ground, your MAP-related problems on your 3.3L V6 mini-van should be resolved.

MAP Sensor Code Won't Go Away

There are quite a few issues that can trick the PCM in your 3.3L V6 mini-van into thinking the MAP sensor's faulty —when it's actually fine.

If you've already tested or replaced the MAP sensor, but that trouble code keeps coming back (even after clearing it and taking the min-van for a test drive), here are a few other things to check that might point you in the right direction:

• Major vacuum leak: A leak at the intake manifold gasket or from cracked/brittle vacuum hoses will throw off the vacuum readings, which in turn messes up the MAP sensor's output.
• Low compression problem: If multiple cylinders have poor compression, the engine will idle rough and create weak or unstable vacuum signals. Run a compression test to rule this out:
  • How To Test Engine Compression (1991-2007 3.3L V6 Chrysler, Dodge, Plymouth Mini-Van).
• Intermittent MAP sensor failure: Sometimes the MAP sensor acts up only now and then. Most of the time it works fine, but occasionally it stops working.
  • One trick I've used is gently tapping the sensor with the handle of a screwdriver while applying vacuum. If the voltage signal jumps around (glitches), it's failing intermittently and is bad.
• Loose or broken connector: If the MAP sensor's electrical connector has a broken locking tab, it can wiggle loose and cause a intermittent false connection.
• Weak fuel pump: If the fuel pump's on its way out, it might not be delivering enough fuel or pressure to the injectors. A fuel pressure test will help confirm this.
  • How To Test The Fuel Pump (1992-1993 3.3L V6 Chrysler, Dodge, Plymouth Mini-Van).
• Stuck open EGR valve: On engines equipped with an EGR valve, one that's stuck open can seriously throw off engine performance and vacuum readings.

More 3.3L Chrysler, Dodge, And Plymouth Mini-Van Tutorials

You can find a complete list of tutorials in this index:

• 3.3L V6 Chrysler/Dodge/Plymouth Mini-Van Index Of Articles.

Here's a sample of the tutorials you'll find in the index:

• 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).