TEST 2: Making Sure The CKP Sensor Is Getting Power
Like any other electrical device, the crankshaft position sensor on your 4.3L, 5.0L and 5.7L equipped GM vehicle needs power to function. This power is in the form of 12 Volts DC that are instantly made available to the crank sensor as soon as you turn the key to the ON position.
This test will help you to confirm that 'YES, the sensor is getting power' or 'NO, it's not getting power'. As in the previous test, you'll be using your multimeter to verify this voltage signal.
These are the test steps:
- 1
Place the multimeter in Volts DC mode.
- 2
Disconnect the crankshaft position sensor from its electrical connector.
- 3
Connect the red multimeter test lead to the wire labeled with the letter A in the photo.
- 4
Connect the black multimeter test lead to the battery negative (-) post.
- 5
Turn the key ON but don't crank the engine.
- 6
Your multimeter should and will register 10 to 12 Volts.
Now, let's take a look at what those voltage readings (or lack of) mean:
CASE 1: 10 to 12 Volts registered on the multimeter when the ignition was turned ON. This is the correct test result and it confirms that the crankshaft position (CKP) sensor is getting power.
The next test is to check that the CKP sensor has a good path to Ground. Go to: TEST 3: Making Sure The CKP Sensor Is Getting Ground.
CASE 2: 10 to 12 Volts DID NOT register when the ignition was turned ON. This result indicates that the ignition module is not supplying power to the crank sensor.
This result exonerates the crankshaft position (CKP) sensor as the cause of the 'cranks but does not start' problem you're trying to solve, since without these 12 Volts, the crank sensor can not create a signal.
Power comes from the ECM fuse in the instrument panel fuse box. Check to see if the fuse is blown.
TEST 3: Making Sure The CKP Sensor Is Getting Ground
The 3-wire crankshaft position sensor has its own independent Ground path, and this path to Ground is provided by the circuit (wire) labeled with the letter B in the photo in the image viewer.
There are several ways to test for Ground in any given circuit, but you need to be very careful, since the fuel injection computer is the one that provides this Ground path internally. Accidentally or intentionally shorting this circuit to battery 12 Volts will fry the computer.
OK, here's the test:
- 1
Place the multimeter in Volts DC mode.
- 2
Disconnect the crankshaft position sensor from its electrical connector.
- 3
Connect the black multimeter test lead to the wire labeled with the letter B in the image above.
- 4
Connect the red multimeter test lead to the battery positive (+) terminal.
- 5
Turn the key ON but don't crank the engine.
- 6
Your multimeter should register 10 to 12 Volts DC.
Now, let's take a look at what those voltage readings (or lack of) mean:
CASE 1: The multimeter showed 10 to 12 Volts when the ignition was turned ON. This is the correct test result and it lets you know that the fuel injection computer is providing a good Ground path for the crank sensor.
So, taking into account that in TEST 1 you DID NOT get the 5 Volt ON/OFF signal and in TEST 2 your multimeter did register 12 Volts, then you confidently conclude, beyond a shadow of a doubt, that the CKP sensor is bad. Replacing the CKP sensor will solve the 'no-start no-spark' problem your vehicle is experiencing.
CASE 2: The multimeter DID NOT show 12 Volts when the ignition was turned ON. This result indicates that the fuel injection computer is not supplying a Ground path to the crank sensor.
This result exonerates the crankshaft position (CKP) sensor as the cause of the 'cranks but does not start' problem you're trying to solve, since without a Ground path, the crank sensor can't create a signal.
Its extremely rare for a problem to occur with this circuit, I myself have never seen it. But if this is the result you obtained, then the next step is to check that there isn't an open-circuit problem in the wire between the fuel injection computer and the crank sensor.
Related Test Articles
If you need to diagnose the ignition system, like let's say you need to test the ignition control module, or the ignition coil, etc., on your 4.3L, 5.0L or 5.7L equipped GM Pick Up or SUV, I have written 2 in depth troubleshooting articles that you'll find at easyautodiagnostics.com:
- How To Test The GM Ignition Control Module (1995-2005) (at: easyautodiagnostics.com).
- How To Test A Misfire / No Spark-No Start Condition (4.3L, 5.0L, 5.7L 96-04) (at: easyautodiagnostics.com).
Here, in this Site, you'll quite a few GM articles and you can check out the complete list of articles by going to the GM Index of articles by clicking here:
Reader's Real Life Case Studies And Solutions
In this section is input and feedback from all of the folks who have had a similar issue with their vehicle and found a solution. If you're one of them, I want to thank you for sharing your experience with all of us!
If you want to share your repair and/or diagnostic experience, you can use the contact form below.
Real Life Case Study 1
Vehicle: 1996 Chevy 1500 pickup, 5.7L
Trouble Codes: None
Complaint: NO START, NO FUEL and NO SPARK “The truck would crank but not start. I had no fire going to any of the spark plugs and the fuel injectors were not working. The mechanic told me that the spider fuel injector was bad because the fuel injector fuse was getting blown, but since the whole thing was so expensive, i decided to park it for a few days. a few days turned into a couple of weeks. Im glad i waited because the fuel injector assembly wasn't the problem anyway, it would have been a waste of money.”
Test Notes: “I read your write up on testing the crank sensor and the symptoms matched the ones on my pick up. I got my multimeter out and did the test myself.”
Repair: REPAIRED SHORTED CRANK SENSOR WIRE “Turned out that I was missing voltage to the crank sensor because the crank sensor wiring had come loose and came in contact with the exhaust manifold and shorted. This is what was burning the fuel injector fuse too. I repaired the burned wire and secured the wiring with plastic ties and replaced the fuse and the pick up started. man, i was happy, thanks for saving me a lot of money. ”
Courtesy of: Steve J. Wilson.
Real Life Case Study 2
Vehicle: 1997 Silverado 1500 pickup, 2 wd, 5.7 liter Vortec 140,000 miles
Trouble Codes: None
Complaint: “We've had the truck for 2 years. ~140,000 miles on it. Intermittently stalls or won't start until multiple attempts, but eventually does after sitting for seconds, minutes, or hours. We've had our mechanic diagnose and replace or direct us to someone else to replace the gas tank, fuel pump,fuel filter, catalytic converter, distributor (twice), coil, and module. Probably more. So many I've forgotten them all. Problem still exists. Someone mentioned the crank sensor as the culprit and Answers.com describes symptoms just like we've had when that sensor goes bad..”
Test Notes: None.
Repair: REPLACED CRANK SENSOR “This morning I took a gamble and bought a new sensor at a local parts store for ~$60. It wasn't particularly hard to replace, plugging into a receptacle behind and beneath the harmonic balancer on the left side of the engine's front cover. I used one of the two shims included which the instructions say to use on older engines. My wife turned the key and vroooom! All the problems seem to have magically disappeared. I'll keep my fingers crossed since we've followed so many false leads with trying to fix the thing in the past, but my wife has driven it more than once today and happily reports that there's no more difficulty starting, it hasn't stalled on her once, and there's no more hesitation with acceleration.”
Courtesy of: Clay C.
If this info saved the day, buy me a beer!
