The 3X-18X crankshaft position (crank) sensor, on the GM 3.8L V6 engine, can easily be tested (to find out if it's bad or not) with a multimeter. With this article, I'll walk you thru' the entire crank sensor testing process in a step-by-step manner.
In case you're wondering if you can test the crank sensor with a simple resistance test (ohms)... let me tell you that it's not possible. That's right... the 3X, 18X crank (CKP) sensor can not be tested with a simple Ohm (resistance) test. Why? Well, because the 3X, 18X crank sensor is a Hall-Effect Type sensor and this type of sensor does not allow for a resistance test.
A Hall Effect sensor has to be tested in action. The crank sensor test I'm gonna' show you here is one of the most effective and sure ways to troubleshoot the sensor using just a multimeter in Volts DC mode.
If you need to know if this 3X 18X crank sensor test applies to your specific 3.8L GM vehicle, take a look at the ‘Applies To:’ box on the right and scroll with the left/right arrow buttons to see all of the applications. Also, the info in this article is geared towards diagnosing and troubleshooting a ‘cranks but does not start condition - no start no spark condition’.
Here are the contents of the 3.8L crank sensor test at a quick glance:
- Symptoms Of A BAD Crankshaft Position Sensor.
- How The 3X, 18X Crank (CKP) Sensor Works.
- How To Read The 3X 18X CKP Images.
- CKP TEST 1: 3X Signal Test.
- CKP TEST 2: 18X Signal Test.
- CKP TEST 3: Power Circuit.
- CKP TEST 4: Ground Circuit.
- Where To Buy The Crank Sensor And Save.
- Related Test Articles.
Tools You'll Need:
- Jack Stands
- 1/2 inch Ratchet Wrench
Symptoms Of A BAD Crankshaft Position Sensor
The most obvious symptom of a BAD crank sensor is your vehicle's engine not starting. In automotive tech terms, this condition is better known as a ‘cranks but does not start condition’.
Below is a simple list of more specific symptoms that accompany a BAD crank sensor:
- The ignition system will not produce spark:
- No spark from all of the coil pack towers.
- No spark from all of the 6 spark plug wires.
- The PCM (Powertrain Control Module=Fuel Injection Computer) will not pulse the fuel injectors.
- If your vehicle is an OBD II equipped vehicle (1996+), the PCM may set a specific BAD crankshaft position sensor diagnostic trouble code (DTC):
- P0336 18X Reference Signal.
- P1374 3X Reference Signal.
Taking all of the above into account, the most important thing to remember is that if you get spark from any spark plug wire... the crank sensor is working and the test in this article won't help you.
How The 3X 18X Crank (CKP) Sensor Works
The 3X 18X crankshaft position sensor is two crank sensors in one assembly and is a Hall-Effect type sensor that needs an external power and ground source to create its crank (CKP) signal. As such, it produces an On/Off DC voltage signal that can be measured with a multimeter, an Oscilloscope, and even an LED Light.
Here, in a nutshell, is 3.8L/how the crank sensor works:
- When you turn the key and crank the engine
- The crank sensor gets power directly from the ignition control module (ICM).
- This power is in the form of 10 Volts DC.
- As the crank pulley starts to turn
- The vane assembly (attached to the crank pulley) starts to slice thru' the crank sensor.
- One part of the crank sensor produces 3 ON/OFF signals for every one crankshaft revolution.
- The other part creates 18 ON/OFF signals per crankshaft revolution.
- This is the reason the crank sensor is called the 3X 18X crank sensor in some service literature.
- These signals are fed directly to the ignition control module. Once these signals are received:
- The module starts sparking the ignition coil packs.
- The ignition module also creates a Fuel Control signal that it sends to the PCM (Powertrain Control Module=Fuel Injection Computer) to start injecting fuel and a host of other things.
- If any of the above signals goes missing, your 3.8L GM vehicle will crank but not start.
The most important thing to know about the 3X 18X crank sensor is that if it goes BAD, your 3.8L V6 equipped GM car or mini-van will crank but not start due to a lack of spark and fuel injection.