CKP TEST 3: Verifying Ground

Verifying Ground To The Crank Sensor. Crank Sensor Test -No Spark No Start Tests (GM 4.8L, 5.2L, 6.0L)

So far you have confirmed that the crank sensor is not creating a signal and that it's getting fed with 12 Volts.

In this test step, you're going to verify that the crankshaft position sensor is getting Ground. As mentioned earlier, the Ground path is completed inside the PCM.

IMPORTANT: You got to be very careful not to short this wire to battery voltage, or you run the risk of damaging the PCM. Also, do not use a test light to verify this voltage, use a multimeter.

  1. 1

    With your multimeter still in Volts DC mode, probe the wire identified with the letter B in the image viewer, with black multimeter test lead. Do not probe the front of the crank sensor connector to check this Ground. Pierce the wire with an appropriate tool.

  2. 2

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

  3. 3

    When everything is set up, have your helper turn the key to the On position.

  4. 4

    If all is good with this circuit, your multimeter should register battery voltage (12+ Volts).

Choose from the CASES below that best match your specific results:

CASE 1: The multimeter registered 12 Volts DC when the key was turned On. Then the CKP sensor is getting a good Ground. This results confirms that the crankshaft position (CKP) sensor is bad. Replace the CKP sensor.

Here's why: A good working CKP sensor, when it receives power and Ground and the engine is cranking, will generate an ON/OFF 10 Volt signal. Now, in your particular case, in TEST 1 you verified the CKP sensor is not creating its ON/OFF 10 Volt signal. In TEST 2 you confirmed that it's being fed with power (12 Volts) and in this test step, you have verified that it's getting a good Ground. Therefore the CKP sensor is bad. Replace the CKP sensor.

CASE 2: The multimeter DID NOT register 12 Volts DC when the key was turned On. Recheck your connections and try the test again.

If the multimeter still does not register 12 Volts, then this result lets you know that the CKP does not have a good sensor Ground. You have now eliminated the crank sensor as the cause of the no-start condition, since without this Ground, the CKP sensor will not work.

Related Test Articles

For your troubleshooting enjoyment, you might find these articles helpfull:

  1. How To Test The MAF Sensor (at: easyautodiagnostics.com).
  2. How To Test The COP Coils (GM 4.8L, 5.3L, 6.0L, 8.1L) (at: easyautodiagnostics.com).
  3. How To Test The Starter Motor (on car) (at: easyautodiagnostics.com).
  4. How To Bench Test The Starter Motor (at: easyautodiagnostics.com).
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