How To Test The MAP Sensor (1989-1990 5.2L, 5.9L V Dodge Ram Van)

When the manifold absolute pressure (MAP) sensor fails, the check engine lights up, a MAP sensor trouble code (OBD-I Code 13 or 14) will get registered, and engine performance goes out the window.

Good news is, you can test it before swapping it out —and I'll walk you through how to do that in this tutorial.

In case you're wondering, there are three parts to the MAP sensor test: checking the signal it sends, making sure it's getting power, and verifying the Ground. You'll use a multimeter for all three. For the signal test, you'll also need a vacuum pump.

APPLIES TO: This tutorial applies to the following vehicles:

• Dodge Ram B150 Van 5.2L V8: 1989, 1990.
• Dodge Ram B250 Van 5.2L V8: 1989, 1990.
• Dodge Ram B250 Van 5.9L V8: 1989, 1990.
• Dodge Ram B350 Van 5.9L V8: 1989, 1990.

OTHER MAP SENSOR TESTS:

• How To Test The MAP Sensor (1991 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test The MAP Sensor (1992-1997 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test The MAP Sensor (1998-2003 5.2L, 5.9L V8 Dodge Ram Van).

Symptoms Of A Bad MAP Sensor

When the MAP sensor acts up, the check engine light's gonna pop on, and you'll usually get one of these two trouble codes:

• Code 13: MAP Sensor Signal Problem.
• Code 14: MAP Sensor Signal Voltage Too Low or Too High.

Along with one of those codes, here's what else you'll probably notice:

• Rough idle: The engine might shake or idle unevenly.
• Black smoke: You'll likely see black smoke puffing out of the tailpipe, especially when you step on the gas pedal.
• Sudden engine stalls: The engine can stall out anytime —whether you're pressing the gas pedal or not.
• Immediate stall after starting: It starts up, then dies right away.
• Lack of power: Acceleration feels weak, and getting up to speed is a struggle.
• Limp-In Mode: The computer kicks in limp mode to protect the engine, cutting power and hurting gas mileage big time.

NOTE: Sometimes another engine issue (not the MAP sensor) can fool the fuel injection computer into thinking your MAP sensor's bad. That's why it's important to test it before buying a new one.

This tutorial shows you how to bench-test the MAP sensor and figure out if it's actually the problem. If it passes the test, check out this next section:

• MAP Sensor Code Won't Go Away.

How The MAP Sensor Works

Your Dodge Ram van doesn't use a mass airflow (MAF) sensor to figure out how much air is entering the engine. Instead, it runs a "Speed Density" system to figure it out.

In this type of system, here's what the fuel injection computer looks at:

• The MAP sensor for pressure inside the intake manifold.
• The intake air temp (IAT) sensor for incoming air temperature.
• The pickup coil in the distributor for engine speed (RPM).

With those three pieces of info, the computer can estimate how much air the engine's pulling in and decide exactly how much fuel to inject.

Let's walk through what happens when you fire up the engine:

• MAP sensor enabled: The computer powers up the MAP sensor by sending voltage and Ground:
  • VIO/WHT wire: Sends 5 Volts DC to the MAP sensor. This wire hooks up to terminal 3 (check the diagram above).
  • BLK/LT BLU wire: Provides Ground. This connects to terminal 1.
• Monitoring vacuum pressure: Once it's powered, the MAP sensor tracks the vacuum pressure inside the intake manifold.
  • When the engine is idling, manifold vacuum is high (which means pressure is low), so the MAP sensor produces a low voltage signal.
  • When the engine is revved up and vacuum drops (meaning pressure rises closer to atmospheric), the MAP sensor responds by producing a higher voltage signal.
• Fuel injection control: Then, using data from the MAP, IAT, and CKP sensors, the computer figures out the right air-fuel mix and adjusts fuel delivery on the fly.

Alright, now that you've got the basics, let's dive into the testing steps!

Where To Buy The MAP Sensor And Save

You can find a MAP sensor for your Dodge Ram van at almost any auto parts store –but you're probably gonna pay way more for it.

My advice is to shop around online, or at the very least, compare prices. That way, you'll get a good idea of how much money you could save. Here are my recommendations:

Not sure if the above MAP sensor fits your particular Dodge Ram van? 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.

TEST 1: Verifying The MAP Signal

Alright, let's kick things off. The first thing we're gonna do is check if your MAP sensor sends out a changing voltage signal when we apply vacuum to it.

We'll hook up a multimeter to the sensor's signal wire, then use a vacuum pump to apply vacuum.

No vacuum pump? No problem. You can just use your mouth and pull vacuum the old-school way —yep, your lungs'll do the trick.

Here's what we're looking for:

• Good Sensor: The voltage will change smoothly as you apply and release vacuum.
• Bad Sensor: If it's bad, the voltage stays stuck at one number no matter how much vacuum you give it.

NOTE: If you need a new multimeter or vacuum pump, here's what I use and recommend:

• Multimeter: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (at: amazon.com).
• Vacuum pump: HTOMT 2 In 1 Vacuum Pump Test Set (also at: amazon.com).

Here's what you need to do step-by-step:

1. 1

   Unplug the vacuum hose from the MAP sensor.
   
   NOTE: Leave the sensor mounted in place —you don't need to remove it.

2. 2

   Hook up your vacuum pump to the sensor's vacuum port.
   
   IMPORTANT: Keep the sensor connected to its 3-wire harness. It needs to stay powered by the fuel injection computer.

3. 3

   Connect your black multimeter lead to the negative (-) terminal on the battery.

4. 4

   Set the multimeter to Volts DC mode.

5. 5

   Connect the red multimeter lead to the middle wire on the MAP connector.
   
   That middle wire should be dark green with a red stripe (DK GRN/RED).
   
   NOTE: You can back probe the connector or use a wire-piercing probe. More on that here: Wire Piercing Probe.

6. 6

   Turn the key to ON (but don't crank the engine).

7. 7

   You should now see 4.5 to 4.7 Volts DC on your multimeter—this is with the key ON and no vacuum applied.

8. 8

   Apply vacuum using the pump —or your mouth. Watch the voltage drop:
   
   1.) 0 in. Hg ...... 4.7 Volts
   
   2.) 5 in. Hg ...... 3.9 Volts
   
   3.) 10 in. Hg .... 3.0 Volts
   
   4.) 20 in. Hg .... 1.1 Volts
   
   NOTE: Whether you're using your lungs or a pump, that voltage should drop and rise smoothly —no gaps or freezing.

Here's how to read your test results:

CASE 1: Voltage changes as you apply/release vacuum. That means your MAP sensor's working like it should.

If the check engine light keeps coming back with a MAP sensor code, head over to MAP Sensor Code Won't Go Away for what to check next.

CASE 2: Voltage stays stuck. That usually points to a bad MAP sensor.

But don't replace it just yet —we still gotta confirm it's getting power and Ground. Go to: TEST 2: Making Sure That The MAP Sensor Is Getting Power.

CASE 3: Voltage is 0 Volts DC. The sensor might be dead or not getting power or Ground.

Next up is checking power and Ground. Begin with: TEST 2: Making Sure That The MAP Sensor Is Getting Power.

TEST 2: Making Sure That The MAP Sensor Is Getting Power

So far, you've found that your MAP sensor isn't sending out a variable voltage signal (back in TEST 1). Now it's time to make sure the sensor's getting power —because if there's no power, it's not gonna work at all.

The fuel injection computer is the one sending power to the MAP sensor. It does that by feeding 5 Volts DC through the violet with white stripe (VIO/WHT) wire of the MAP sensor's 3-wire connector.

The VIO/WHT wire connects to the terminal labeled with the number 3 in the illustration of the MAP sensor's connector above.

Here's what to do next:

1. 1

   Unplug the MAP sensor from its electrical connector.

2. 2

   Attach the black multimeter lead to the negative (-) battery terminal.

3. 3

   Set your multimeter to measure Volts DC.

4. 4

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

5. 5

   Touch the red multimeter lead to the terminal marked with number 3.
   
   NOTE: Make sure this is the terminal with the VIO/WHT wire going into it.

6. 6

   Your multimeter should show 4.5 to 5 Volts DC.

Now let's break down what those readings mean:

CASE 1: You got 4.5 to 5 Volts. That tells you the fuel injection computer is sending power to the MAP sensor like it should.

Next up is checking if the MAP sensor is getting a solid Ground. To do that, go to: TEST 3: Verifying The MAP Sensor Ground Circuit.

CASE 2: You didn't get 4.5 to 5 Volts. Go back and double-check all your connections, then test again.

If you're still not seeing 4.5 to 5 Volts, then you've found the reason the MAP sensor isn't giving you a changing voltage signal when vacuum is applied or released.

I don't cover how to track down the missing voltage, but the good news is —you've already confirmed the MAP sensor itself isn't the problem.

Now it's all about getting that 5 Volt supply working again. The most common causes for no voltage here are:

• The 5 Volt wire is damaged (open-circuit issue) somewhere between the sensor connector and the fuel injection computer.
• Rare, but possible —the FI computer has an internal fault and isn't sending out the 5 Volts.