TEST 2: Making Sure The MAP Is Getting Power
So far in TEST 1, you have verified that the MAP sensor on your 2.8L Chevy S10 pickup (GMC S15 pickup, GMC Sonoma) is not generating a signal or the signal is stuck in one value.
Before we judge the MAP sensor as defective, we need to make sure it has power. This power is supplied by your vehicle's fuel injection computer and is in the form of 5 Volts DC.
The terminal labeled number 1 in the image above is the one that feeds this power to the manifold absolute pressure (MAP) sensor.
Alright, this is what you'll need to do:
- 1
Place your multimeter in Volts DC mode.
- 2
Disconnect the MAP sensor from its electrical connector.
- 3
Probe the wire that connects to the terminal labeled with the number 1 in the illustration above with the red multimeter test lead.
The wire that connects to terminal 1 is the GRY wire of the 3-wire connector.
NOTE: You can probe the front of the wire's female terminal. If you do, be careful not to damage it with your multimeter's probe. - 4
Now Ground the black multimeter test lead on the battery's negative (-) post.
- 5
Turn the key ON but don't start the engine.
- 6
Your multimeter should show you a voltage value around 4.5 to 5 Volts DC.
OK, now that the testing part is done, let's take a look at what your results mean:
CASE 1: Terminal 1 has 5 Volts DC. This is the correct result.
The next step is to check that the MAP sensor is getting Ground. For this test go to: TEST 3: Making Sure The MAP Is Getting Ground.
CASE 2: Terminal 1 DOES NOT have 5 Volts DC. This results lets you know that the MAP sensor itself is not bad, since without these 5 Volts DC, the MAP sensor can not function.
Although it's beyond the scope of this article to troubleshoot the cause of these missing 5 Volts, your next step is find out why these 5 Volts are missing and restore them.
TEST 3: Making Sure The MAP Is Getting Ground
So far, you have confirmed that:
- You have a MAP sensor trouble code lighting up the check engine light (CEL).
- The MAP sensor is not creating a decreasing/increasing MAP voltage signal (TEST 1).
- The MAP sensor is getting power (TEST 2).
Now, we need to make sure that the MAP sensor is receiving Ground. We'll use our multimeter to confirm the presence of Ground in the terminal labeled with the number 3 in the illustration above.
IMPORTANT: The wire that connects to terminal 3 of the MAP sensor connector connects directly 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
Place your multimeter still in Volts DC mode.
- 2
Disconnect the MAP sensor from its electrical connector.
- 3
Probe the wire labeled with the number 3 in the image above, with the black multimeter test lead.
The wire that connects to terminal 3 is the PPL (or BLK/RED or BLK/ORG) wire of the 3-wire connector.
NOTE: You can probe the front of the wire's female terminal. If you do, be careful not to damage it with your multimeter's probe. - 4
Connect the red multimeter test lead on the battery's positive (+) post.
- 5
Turn the key ON but don't start the engine.
- 6
Your multimeter register 10 to 12 Volts DC.
OK, let's take a look at what your results mean:
CASE 1: The multimeter registered 10 to 12 Volts. This is the correct result and it confirms the MAP sensor is getting Ground.
You can correctly conclude the manifold absolute pressure sensor is bad and needs replacement if you have:
- Confirmed the MAP sensor voltage signal does not decrease/increase as you apply/release vacuum to the sensor (TEST 1).
- Confirmed the MAP sensor is receiving 5 Volts (TEST 2).
- Confirmed the MAP sensor is receiving Ground (this test section).
If you'd like to buy the original AC Delco MAP sensor and save, take a look at the section: Where To Buy The MAP Sensor And Save.
CASE 2: The multimeter DID NOT register 10 to 12 Volts. Double check your multimeter connections and repeat the test.
If your multimeter results still do not indicate 10 to 12 Volts, you can conclude the MAP sensor itself is not bad and not the cause of the MAP diagnostic trouble code (DTC) issue.
Although it's beyond the scope of this article to troubleshoot the cause of this missing Ground, your next step is find out why Ground is missing and restore it.
MAP Sensor Code Won't Go Away
So you have tested the MAP sensor and according to the test results, it is good. But the check engine light keeps coming back on even after you clear the diagnostic trouble code (DTC) from the computer's memory.
Well, here are a couple of suggestions that might inspire your next diagnostic move:
- 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.
- The fuel pump is failing and is not sending enough fuel and/or fuel pressure up to the fuel injectors. I suggest a fuel pump test.
- The fuel injection computer is bad (internal short). Although this problem is not very common, it does happen.
Before you jump the gun and start replacing the above, test the components first. This will help you save time, money, and the frustration of replacing parts your vehicle does not need.
More 2.8L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials
You can find a complete list of tutorials for the 2.8L V6 Chevrolet S10 pickup, GMC S15 pickup, and GMC Sonoma in this index:
Here's a sample of the articles, you'll find in the Index of Articles:
- How To Test The Fuel Pump (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test Engine Compression (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The EGR Valve (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- How To Test The Starter Motor (1988-1993 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup).
If this info saved the day, buy me a beer!
