How To Test The Crank Sensor (Ford 3.0L, 3.8L)

The clearest indication that the crank sensor on your Ford 3.0L or 3.8L car, minivan or pickup has failed, is a cranks but does not start condition.

Since so many things can cause a no-start problem, it's always a good idea to tests the components suspected of causing the no-start first before replacing them. In this article, I'll show you how to test the crank sensor with a multimeter in Volts AC mode.

Important Tips And Suggestions

TIP 1: The crank sensor is located right behind the crankshaft pulley, since the crank sensor's reluctor wheel is behind (and part of) the crank pulley.

TIP 2: Since this is an on-car test of the crank sensor, you'll need to crank the engine to test it. For this reason, the battery on your Ford vehicle must be fully charged.

TIP 3: You'll need to jack up the vehicle to gain access to the crank sensor. Use a jack stand to hold the car up in the air. Do not trust the jack! Wear safety glasses to protect your eyes from falling debris. Think safety all of the time (your safety is your responsibility)

TIP 4: When the crank sensor goes bad, you'll get a no-spark no-start condition. So, if you're getting spark, even if in just one cylinder, the crank sensor is good and this test will not help you.

Symptoms Of A Bad Ford Crank Sensor

When the crank sensor goes bad on your Ford 3.0L or 3.8L vehicle, the very first symptoms you'll see is a 'no-start no-spark' condition affecting your car.

Here are some more specific symptoms of a bad crank sensor:

1. Your 3.0L or 3.8L car (pickup, minivan) will 'crank but not start'.
   • So if your car starts, the crank sensor is working.
2. The PCM (Powertrain Control Module= Fuel Injection Computer) will not pulse any of the 6 fuel injectors.
   • You can easily verify this with a Noid light test. If the Noid light flashes ON and OFF, the crank sensor is OK.
3. No spark coming out of any of the 6 spark plug wires.
   • You can check this with a simple spark test and if you've got spark, the crank sensor is OK and doing its job.
4. The coil pack will not get any switching signals from the PCM (Powertrain Control Module = Fuel Injection Computer).
5. Sometimes (but usually never), the PCM will set a diagnostic trouble code to indicate a problem with the crank sensor:
   • P0320: Erratic Profile Ignition Pickup (PIP) pulses.

How Does The Crank Sensor Work

The crank sensor on your 3.0L, 3.8L Ford car or minivan is a two wire reluctor type. Ford labels this sensor as a magnetic transducer type.

In plain English, this means that this type of crank sensor creates its own voltage signal without an external power source. Here are some more specifics:

1. As the engine starts to crank, the trigger wheel mounted on behind the front crankshaft pulley starts to rotate.
   • The trigger wheel has a total of 35 teeth spaced 10 degrees apart, with one empty space for a missing tooth.
2. As this trigger wheel's teeth pass under the crank sensor, they induce the crank sensor to create an A/C voltage that the PCM uses to activate the ignition coil pack and the fuel injectors.
3. The primary indicator of the crankshaft speed and piston Position is the missing teeth on the trigger wheel.
4. The PCM then uses this info to activate:
   • The ignition coil pack.
   • Fuel injectors.
   • The PCM also uses the crank sensor signal to activate the tachometer on your instrument cluster (if equipped).

Bottom line is that if the crank sensor fails in your Ford vehicle, it's not going to start due to a lack of spark and fuel.

Checking The CKP Signal With A Multimeter

Since the crank sensor on your Ford vehicle is a 2-wire reluctor type sensor, it can be easily tested with your multimeter set to AC Volts mode.

Just a friendly reminder: the battery should be fully charged so that you can crank the engine for several seconds while you observe your multimeter.

One last thing before we start: If your Ford vehicle has spark coming out of at least one spark plug wire, this tells you that the crank sensor is producing a signal and functioning correctly.

CAUTION: To access to the crankshaft position sensor (to test it), the vehicle has to be lifted. Once you've got it up with a jack, make sure to set it securely on jack stands. Don't ever rely on the jack by itself to keep your vehicle raised.

NOTE: To connect your multimeter to the two CKP sensor wires, you'll need to use wire-piercing probes. If you don't already own some, here's the exact tool I use and recommend: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

OK, let's get'er done:

1. 1

   Disconnect the ignition coil pack from its electrical connector.
   
   NOTE: This is an important safety precaution to keep the engine from starting (in case it decides to start).

2. 2

   Disconnect the crank sensor from its connector and peel back some of the wire loom or the black electrical tape covering the two CKP sensor wires.

3. 3

   Hook one of your multimeter leads to one of the CKP sensor wires.
   
   It doesn't matter which lead (red or black) you use, since polarity isn't important here.
   
   NOTE: You'll need to use a wire-piercing probe to connect the test lead to the wire.

4. 4

   Attach the other multimeter lead to the other CKP sensor wire.

5. 5

   Plug the connector back into the crank sensor.
   
   IMPORTANT: Keep your test leads and probes clear of the crank pulley and serpentine belt, because the engine will be cranking in the next step.

6. 6

   Switch your multimeter to Volts AC mode.

7. 7

   With the engine not cranking, your multimeter should read 0 Volts AC.

8. 8

   Have a helper crank the engine while you watch the multimeter.

9. 9

   You should see the voltage fluctuate between about 0.5 and 1 Volt AC while the engine is cranking.
   
   To be clear, the multimeter won't show a steady AC voltage. The reading will fluctuate between 0.5 and 1 Volt AC the whole time the engine is cranking —and only while it's cranking.

Let's figure out what your test result means:

CASE 1: The multimeter showed the expected AC voltage while the engine was cranking. This tells you the CKP sensor is producing a proper signal and is in good working shape.

CASE 2: The multimeter DID NOT show the expected AC voltage while the engine was cranking. This points to a failed crank sensor and explains the 'cranks but will not start' problem.

According to Ford repair manual, the crank sensor should generate more than 0.4 Volts AC. If it’s not reaching that level, the next step is to measure the sensor’s internal resistance, which should fall between 300 and 800 Ohms.

Where To Buy The Crank Sensor And Save

If you're ready to replace the CKP sensor on your Ford vehicle, I want to recommend the following sensors from known automotive brands I've been using forever and don't hesitate to recommend:

NOTE: Not sure if the CKP sensor fits your particular Ford/Mercury? Don't worry, once you get to the site they'll make sure it fits by asking you the specifics of your particular Ford vehicle. If it doesn't fit, they'll find you the right crank sensor.

Related Articles

Here, at troubleshootmyvehicle. Com, there are several more 3.0L or 3.8L tutorials that you can read at: Ford 3.0L, 3.8L Index Of Articles.

At easyautodiagnostics. Com (the other site I write for) you can find the following:

• How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L) (at: easyautodiagnostics.com).
• How To Test The Ford Mass Air Flow (MAF) Sensor (at: easyautodiagnostics.com).