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

TEST 3: Verifying The MAP Sensor Ground Circuit

The last two tests told us two key things:

• The MAP sensor isn't putting out a changing voltage when you apply or release vacuum (TEST 1).
• The sensor is getting power —4.5 to 5 Volts DC (TEST 2).

Now for the final check —we're gonna see if the MAP sensor is getting Ground through the black with light blue stripe (BLK/LT BLU) wire on its 3-wire connector.

This one's simple, and you'll use your multimeter again to run a voltage check.

IMPORTANT: That BLK/LT BLU wire goes straight to the fuel injection computer, so don't short it out by touching it to 12 Volts. That'll fry the computer. Stick to multimeter voltage test I'm outlining below. It's a safe way to check the wire for Ground.

Here's how to do it:

1. 1

   Unplug the MAP sensor from its electrical connector.

2. 2

   Connect the red multimeter lead to the battery positive (+) terminal.

3. 3

   Switch your multimeter to Volts DC mode.

4. 4

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

5. 5

   Touch the black multimeter lead to the terminal marked with number 1.
   
   NOTE: Make sure this terminal corresponds to the BLK/LT BLU wire.

6. 6

   Your multimeter should read between 10 and 12 Volts DC.

Now, what those results mean:

CASE 1: You got 10 to 12 Volts. That confirms the MAP sensor is getting Ground from the computer.

This means your MAP sensor is toast —only if you've already confirmed:

• It's not producing a variable voltage signal when vacuum is applied/released (TEST 1).
• It's receiving proper power (TEST 2).
• It's also getting a solid Ground (this section).

Need to replace it? You can save a few bucks with my recommendations here: Where To Buy The MAP Sensor And Save.

CASE 2: You didn't see 10 to 12 Volts. Double-check everything and test again.

If there's still no voltage reading, that's why the MAP sensor isn't sending out a variable signal when you hit it with vacuum.

In this tutorial I don't go into troubleshooting that missing Ground, but here's the good part —you now know the sensor itself isn't the issue.

Your next move is restoring that Ground circuit. Here are the most common causes behind the missing Ground:

• The Ground wire's damaged somewhere between the sensor connector and the fuel injection computer.
• Rare case: there's an internal failure in the computer itself.

MAP Sensor Code Won't Go Away

Alright, so you've tested the MAP sensor and it looks like it's working fine. But the check engine light is still coming back —even after you cleared the diagnostic trouble code (DTC) from the computer. So what gives?

Here are a few things that could still be behind the problem:

1. Major vacuum leak: A big vacuum leak is throwing off the air/fuel mixture, making it lean. That can cause the engine to idle rough and trick the fuel injection computer into blaming the MAP sensor.
2. Cracked or dry-rotted vacuum hose: The rubber hose connecting the MAP sensor to the vacuum outlet on the intake manifold might be cracked or even broken. If that hose's leaking vacuum, the MAP sensor won't report a correct intake manifold vacuum pressure.
3. Low engine compression: If multiple cylinders have low compression, the engine will idle rough and intake vacuum will be inconsistent. That can mess with the MAP sensor readings. To rule this out, run a compression test:
   • How To Test Engine Compression (1989-2003 5.2L, 5.9L V8 Dodge Ram Van).
4. Intermittent failure: Sometimes the sensor works, sometimes it doesn't. To catch this, try gently tapping it with the handle of a screwdriver while applying vacuum. If the voltage signal jumps or drops out, you've found your problem.
5. Loose or damaged MAP sensor connector: The connector is broken/damaged. If the locking tab broke off (a very common issue), it could be slipping loose and causing intermittent connection issues.
6. Weak or failing fuel pump: The fuel pump could be on its way out. If it can't deliver enough fuel, your engine runs lean and idle rough. Check the fuel pressure to make sure it's within spec.

More 5.2L, 5.9L V8 Dodge Ram Van Tutorials

I've written several more tutorials that may be of interest to you that you can find in this index:

• 5.2L, 5.9L V8 Dodge Ram Van Index Of Tutorials.

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

• How To Test The TPS (1989-1990 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test The Intake Air Temp (IAT) Sensor (1992-1997 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test Engine Compression (1989-2003 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test For A Blown Head Gasket (1989-2003 5.2L, 5.9L V8 Dodge Ram Van).