How To Test The 3.8L GM Crank Sensor With A Multimeter

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 crankshaft position sensor testing process in a step-by-step manner.

In case you're wondering if you can test the crankshaft position 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 crankshaft position 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 crankshaft position 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 crankshaft position 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’.

Symptoms Of A Bad Crankshaft Position Sensor

The most obvious symptom of a bad crankshaft position 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 crankshaft position sensor:

1. 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.
2. The PCM (Powertrain Control Module=Fuel Injection Computer) will not pulse the fuel injectors.
3. 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 crankshaft position sensor is working and the test in this article won't help you.

Where To Buy The Crank Sensor And Save

You can find the crankshaft position sensor just about in anywhere. The best place to buy it and the harmonic balancer (if the crankshaft position sensor blades are bent or damaged) and save a few dollars is online.

The following links will help you comparison shop for the original AC Delco and aftermarket crankshaft position sensor and the crankshaft pulley (harmonic balancer):

How The 3X 18X Crank (CKP) Sensor Works

The 3X 18X crankshaft position sensor is two crankshaft position 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 how the crankshaft position sensor works:

1. When you turn the key and crank the engine
   • The crankshaft position sensor gets power directly from the ignition control module (ICM).
   • This power is in the form of 10 Volts DC.
2. As the crank pulley starts to turn
   • The vane assembly (attached to the crank pulley) starts to slice thru' the crankshaft position sensor.
   • One part of the crankshaft position 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 crankshaft position sensor is called the 3X 18X crankshaft position sensor in some service literature.
3. 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.
4. 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 crankshaft position 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.