TEST 1: Testing The CMP Signal With A Multimeter
We'll connect a multimeter to the CMP sensor's signal output wire and make sure that it is producing the correct signal.
The wire that carries the CMP signal to the fuel injection computer is the wire labeled with the letter B in the photo above.
NOTE: The camshaft position sensor must remain connected to its electrical connector for this test to work. You'll need to use a back probe on the connector or a wire piercing probe on the wire. You can see an example of this tool here: Wire Piercing Probe.
IMPORTANT: The engine must be manually turned. In other words, you can not use the starter motor to turn the engine. You'll need to use a 1/2" ratchet and the appropriate socket on the crankshaft pulley (to turn the engine).
OK, let's get started:
PART 1:
- 1
Raise the front passenger side of you vehicle onto a jack stand (for safety).
- 2
Remove the front passenger-side wheel. If the wheel spins as you're trying to break the lug nuts loose, have someone sit inside the vehicle and step on the brake pedal. This will keep the wheel from moving and facilitate the removal of the lug nuts.
- 3
Remove the plastic water splash shield that protects the crankshaft pulley and serpentine belt from water.
- 4
Locate the CMP sensor's connector. This connector is located on top of the front cylinder head valve cover and in front of the upper intake manifold plenum. It may be necessary to remove some of the plastic wire loom protector that shields the three wires of the camshaft position (CMP) sensor.
PART 2:
- 5
Place the multimeter in Volts DC mode.
- 6
Connect the red multimeter test lead to the green (GRN) wire of the 3-wire connector.
The GRN wire is the signal wire that transmits the camshaft position sensor signal to the PCM and is the one labeled with the letter B in the photo.
Remember, the CMP sensor must remain connected to its engine wiring harness connector. - 7
Connect the black multimeter test lead to the battery negative (-) terminal.
PART 3:
- 8
Turn the crankshaft pulley by hand in a clock-wise direction while observing the multimeter.
NOTE: Do not use the starter motor to crank the engine. - 9
If the CMP sensor is working correctly, the multimeter will register an ON/OFF voltage pulse once every two revolutions of the crankshaft.
NOTE: OFF is when the multimeter displays 9.5 to 10 Volts DC and ON is 0 Volts DC.
To be more specific: Your multimeter will register 9 to 10 Volts most of the time you're turning the crankshaft pulley. When the camshaft position sensor is activated (and if it's working correctly) by the pole piece on the camshaft, then this voltage will go down to 0 Volts.
Remember, the multimeter will only register the 0 Volts only once per two complete turns of the crankshaft pulley.
Let's analyze your test result:
CASE 1: The multimeter registered the ON/OFF voltage signal as you manually turn the engine. This is the correct and expected test result and it tells you that the CMP sensor is functioning correctly.
CASE 2: The multimeter DID NOT register the ON/OFF voltage pulse as the crankshaft pulley was hand-turned two full revolutions. This test result usually tells you that the CMP sensor has failed.
To be 100% certain that the CMP sensor is bad, we need to make sure that it's getting power. Go to: TEST 2: Making Sure The CMP Sensor Is Getting 12 Volts.
TEST 2: Making Sure The CMP Sensor Is Getting 12 Volts
The camshaft position sensor receives 12 Volts from the fuel injection computer. Without them, it will not create an ON/OFF output signal.
So in this test we'll check that the wire labeled with the letter A (in the photo above) is delivering 12 Volts to the CMP sensor.
If the wire labeled with the letter A is supplying power to the CMP sensor, the next step is to check that the wire labeled with the letter C is supplying Ground (TEST 3).
Let's get testing:
- 1
Place your multimeter in Volts DC mode.
- 2
Disconnect the CMP sensor from its electrical connector.
- 3
With the red multimeter test lead and an appropriate tool probe the wire labeled with the letter A in the photo above.
NOTE: This test is done on the engine wiring harness connector. - 4
Connect the black multimeter test lead to the negative (-) battery terminal.
- 5
Turn the key to its ON position but don't start the engine.
- 6
The multimeter should display 10 to 12 Volts.
Let's analyze your test result:
CASE 1: 10 to 12 Volts are present. So far so good, since this is the correct hand expected test results.
The next step is to make sure that the CMP sensor is receiving Ground. For this last test go to: TEST 3: Making Sure The CMP Is Getting Ground.
CASE 2: 10 to 12 Volts ARE NOT present. This test result let you know that the CMP sensor is not receiving power. Without these 12:00 it will not create an ON/OFF voltage signal.
The most likely reasons for this are:
- The wire has open-circuit problem.
- The fuel injection computer may be fried (although a very rare thing to happen).
Although it's beyond the scope of this tutorial to test these conditions, you have now eliminated the camshaft position (CMP) sensor itself as bad.
TEST 3: Making Sure The CMP Sensor Is Getting Ground
So far, you have tested and confirmed that:
- The CMP sensor is not creating an ON/OFF voltage signal (TEST 1).
- The wire labeled with the letter A is supplying 10 to 12 Volts DC.
In this test section, we'll check that the wire labeled with the letter C is supplying Ground to the CMP sensor.
We'll perform a multimeter voltage test to check the presence of Ground in this wire.
IMPORTANT: The fuel injection computer is the one that provides this Ground internally, so be careful and don't accidentally or intentionally apply power (12 Volts) to this wire or you'll fry the fuel injection computer.
OK, here are the test steps:
- 1
Place your multimeter in Volts DC mode.
- 2
Disconnect the CMP sensor from its electrical connector.
- 3
With the black multimeter test lead and an appropriate tool probe the wire labeled with the letter C in the photo above.
NOTE: This test is done on the engine wiring harness connector. - 4
Connect the red multimeter test lead to the positive (+) battery terminal.
- 5
Turn the key to its ON position but don't start the engine.
- 6
The multimeter should display 10 to 12 Volts.
Let's take a look at your test results:
CASE 1: The multimeter showed 10 to 12 Volts. This test result confirms that the CMP sensor is receiving Ground.
You can conclude that the CMP sensor is bad and needs replacement if you have:
- Confirmed that the CMP sensor is not creating an ON/OFF voltage signal (test 1).
- Confirmed that the CMP sensor is receiving 10 to 12 Volts (test 2).
- In this last test section, that the CMP sensor is receiving Ground.
If you'd like to save some bucks on the CMP sensor, consult my recommendations here: Where To Buy The CMP Sensor And Save.
CASE 2: The multimeter DID NOT show 10 to 12 Volts. This tells you that the CMP sensor is not receiving Ground and without it it will not function.
The most likely reasons for this missing Ground are:
- The wire has open-circuit problem.
- The fuel injection computer may be fried (although a very rare thing to happen).
Although it's beyond the scope of this tutorial to test these conditions, you have now eliminated the camshaft position (CMP) sensor itself as bad.
More 3.1L V6 Buick, Oldsmobile Tutorials
You can find a complete list of 3.1L V6 Buick (Oldsmobile) tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test Engine Compression Test (3.1L V6 Buick, Oldsmobile).
- How To Test A Blown Head Gasket (3.1L V6 Buick, Oldsmobile).
- How To Test The Fuel Pump (3.1L V6 Buick, Oldsmobile).
- How To Test The 24X Crankshaft Position Sensor (1995-1997 3.1L V6 Oldsmobile Cutlass Supreme).
If this info saved the day, buy me a beer!
