Crankshaft Position Sensors - Function, Failure, Diagnosis, Testing

Crankshaft position sensors, produce a signal, that talks to the engine control module (ECM) / engine control unit (ECU).

Consequently, providing the exact position of the crankshaft, as it rotates in the engine.

So, now the computer can translate that information into, the exact position of the pistons. While, they come up or go down in the compression cycle.

So, what do Crankshaft Position Sensors actually do, and why do we need them. I’ll start by explaining the specific role, that crankshaft position sensors play, in the electronic ignition system. This info applies to whatever make, and model you may be driving. So, whether it’s a Ford, Chevy, Chrysler, Dodge, Jeep, Nissan, Honda, Toyota, or whatever, this primer will help.

In A Nutshell, The Crankshaft Position Sensors Function Is:

It detects the exact position of the crankshaft, while it is rotating in the engine.
Next, it turns that information into, a series of repetitive electrical voltage impulses.
Finally, it sends that information to the engine control unit (ECU), in a digital format.

Lastly, this signal can be either an, Analog Voltage Signal or a Digital DC Voltage Signal. But, more about this a little later. All this is so that the vehicle’s engine, will start and stay running. So, with this information the Fuel Injection Computer / Ignition Control Module, knows the exact time to make the spark.

So, Camshaft Position Sensors Are GENERALLY Used, In All Modern Fuel Injected Engines.

This is to fine tune ignition timing and fuel injection timing, after the vehicle has started. Although this article concentrates on (CKP) sensors, you can apply most of this info, to the (CMP) sensors too.

The (CKP) sensor signal triggers the Ignition Module / Fuel Injection Computer. The trigger starts switching, the ignition coil primary current ground path, On and Off. I usually refer to the sensor’s signal as, the “Triggering Signal”.

Since the (CKP) sensor is the one, producing this “Triggering Signal”, I refer to it as the “Triggering Device”.

So, the signal that the Computer sends the Ignition Coil for it to start sparking, is the “Switching Signal”.

And, guess what… the Ignition Module / Fuel Injection Computer is therefore, the “Switching Device”.

So, the Ignition Control Module really doesn’t send a physical signal, to the Ignition Coil(s). (like the Crank or Cam sensor does, to the “Switching Device”) Why? Well, because the term “Switching Signal” is just a descriptive name. Covering, the turning on and off, of the primary current passing thru’ the Ignition Coil.

In conclusion, this turning on and off only happens. After the Ignition Module / Fuel Injection Computer receives the (CKP) sensors Signal. Finally, As you may already know, it’s this action that causes, the Ignition Coil to start firing the Spark.

Common Failure Symptoms, Of Bad Crankshaft Position Sensors

We can take for granted that when a (CKP) sensor goes BAD, your vehicle will not start. It’ll crank, but not start.

But hey, an engine could not start, due to a ton of different reasons like:

A BAD Fuel Pump
BAD Ignition Coil
A BAD Ignition Control Module
BAD Spark Plug Cables

Therefore, it’s not enough to say that your engine won’t start. What you need to know is, some of the measurable, testable effects and symptoms. That a BAD (CKP) sensor, has on the Ignition System.

And so, if the (CKP) sensor, isn’t creating a Signal. Then, the measurable, testable effects of this condition are, but not limited to:

No Fuel Injector Pulse
The “Triggering Device” (whether it’s the Ignition Control Module or the F.I. Computer). Will, not produce a “Switching Signal”, to the Ignition Coil.
No Spark coming out of the, Ignition Coil or Coils.
In addition on some makes, like Chrysler/Dodge/Jeep, the Fuel Injection Computer. Will, not continue to power the Fuel Pump / Ignition System with 12 Volts. After, an initial ten seconds or so.

What Tools Do You Need To Test, Crankshaft Position Sensors?

You don’t need expensive tools and/or expensive testing equipment, to test these (CKP) and (CMP) sensors.

Here’s what you’ll need:

The vehicles battery, must be Fully Charged.
A Digital Multimeter that can read, Hertz Frequency.
A good Repair Manual, will probably be just one of many information resources that you’ll use.
You’ll need someone to help you crank the engine over. While, you observe the readings, on the Multimeter.
A Fuel Injector Noid Light.
You don’t need, an Automotive Scan Tool.
You don’t need, an Oscilloscope.

Do I Need An Automotive Scan Tool, To Test The (CKP) And (CMP) Sensors?

I’ve already covered this ground a bit, but I’ll restate that, these sensors are tested, without a Scan Tool. Now, before I ruffle some feathers… let me explain. The majority of vehicles on the road, will not set a (CKP) sensor code, when the sensor goes BAD.

This is not an absolute truth, mind you. But, in my experience, about 95% percent of the BAD (CKP) sensors that I’ve replaced. The vehicle’s onboard self-diagnostics, didn’t leave any type of crankshaft position sensors code! As you might already know, such a code (or codes) can give you an idea of what is going on. And, where to start the diagnostic process.

OK, even if you tried using a Scan Tool, most makes and models will not let you have access to, the live Data. To be able to read the (RPM)’s that the Scan tool provides, while you’re cranking the engine.

So, if you have no live Data, you won’t see an (RPM) signal, on the Scan Tool display screen. (in case you didn’t know, the Scan Tool displays the (RPM)’s from info from the (CKP) sensor). Therefore, knowing how to test them with a multimeter independent of a Scan Tool, becomes very important. (or an LED or an oscilloscope or whatever).

Now, when it comes to (CMP) sensors… a Scan Tool, does come in handy. Because, a BAD (CMP) sensor, does register a diagnostic code. This code usually lights up your check engine light (CEL), on your instrument cluster. But, testing them requires a method that is independent of the Scan Tool. And well, as I’ve mentioned before. The test steps that apply to a (CKP) sensor, also apply to a (CMP) sensor.

Basic Circuit Description, Of A THREE Wire Sensor?

On this type of sensor, each of the three wires, has a specific job to do. Here’s the breakdown:

One wire is the Power Source and it normally provides 12 Volts, although some provide 9 Volts. You’ll test for this Voltage with your, Multimeter in DC Volts mode.
One wire is the Ground Path for the, above 9 or 12 volts. This Ground is generally provided inside the Fuel Injection Computer or the Ignition Control Module, but not always. You’ll test for this Ground, with your Multimeter in DC Volts mode.
The third wire is the Triggering Signal wire. Hence it’s thru’ this wire that the Crank (or Cam sensor) sends the Signal it produces. To the Fuel Injection Computer or Ignition Control Module.
It’s on this wire that you’ll connect the Red Lead of your, Multimeter to test for the Signal.
The Black Lead, you’ll connect to ground.
The Multimeter will have to be either in, Volts DC mode or Frequency (Hz) mode, to verify the Signal.
Finally the rule of thumb, if you’re using Volts DC mode. Is, that this Signal should output the amount of Voltage that comes into, the sensor on the Power Circuit. So, when you crank the engine, you should see anywhere between 9 to 12 Volts.
If the (CKP) or (CMP) sensor is BAD, you’ll get no reading.

Basic Circuit Description, Of A TWO Wire Sensor

Since this type of sensor only has two wires and no Power Supply, testing them is not that hard:

One of the two wires is the Signal wire. Consequently, sending the Signal to the Fuel Injection Computer or Ignition Module. The other wire acts, as a Ground return. Furthermore, this Ground is always provided by, the Fuel Injection Computer or the Ignition Control Module.
On this type of sensor, you’ll connect, both Multimeter Leads to both wires. That is the Red Lead can be connected to either of the two. The Black Lead is connected to the remaining one. It doesn’t matter which Lead goes where, since the polarity does not matter.
Your Multimeter has to be in, Volts AC mode to see this Signal.
When your helper cranks the engine, the Multimeter will display about 1 Volt AC. Finally, this AC Voltage will move between .3 Volts AC to 1 Volt AC. The whole time the engine is cranking, this is normal. If the sensor is BAD, the Multimeter will not display, any AC Voltage.
This Voltage increases with Engine (RPM)’s. So the faster the engine cranks, the higher the AC Voltage.

The Following Testing Path Applies To A, Cranks But Does NOT START Condition

Testing crankshaft position sensors isn’t hard, and the diagnostic flow is pretty straightforward.

Consequently, the following tests only apply to a Crankshaft Position Sensor, that has failed completely. But, with some modification, you can also follow the same diagnostic path, in diagnosing a (CMP) Sensor.

What Are The Actual Testing Steps:

STEP ONE:

Make certain that the Battery is in a, fully charged condition.
Test for Spark:

You’ll need to Test for Spark at all cylinders, to be certain that there’s no Spark present at all.
If Spark is present, the Crankshaft Position, is working properly.
Test for Fuel Injector Pulse, although depending on the fuel system design, this is not always possible.
If the Fuel Injector Pulse is present, the Crankshaft Position sensor, is working properly.

STEP TWO:

Find the location of the, Crankshaft Position sensor.
Determine type of (CKP) sensor (either a two or three wire type).

THREE:

On three wire type, CKP sensors:

Determine which wire, is the Power Circuit.
Which wire, is the Ground Circuit.
Determine which wire, is the Signal Wire.

On two wire type, crankshaft position sensors:

You don’t have to determine which wire is which, since you don’t have to test for a power supply. Also, the Multimeter leads are hooked up to both wires, at the same time. To read the Signal the sensor produces.

STEP FOUR:

On three wire type CKP sensors:

Probe the Power Circuit to verify the presence of the specified Voltage. This Voltage is usually confirmed with the key on or engine cranking.
The Ground Circuit to verify that ground does exist. This Ground is usually confirmed with the key on or engine cranking.
Probe the Signal Wire. Since the presence of this Signal can only be confirmed, with the engine cranking. And, with the Multimeter in Hertz (Hz) Frequency Mode or in Volts DC Mode.

On two wire type CKP sensors:

Probe both wires coming out of the sensor, with both leads of your Multimeter. The polarity of the leads doesn’t matter. In other words, the red and black lead, can go to any of the two wires.
The presence of this Signal can only be confirmed, with the engine cranking, and with the Multimeter in Volts AC.

STEP FIVE:

If no Signal is present:

The Crankshaft Position sensor is BAD, replace it.

If a Signal is present:

The Crankshaft Position sensor is good.

(CKP) & (CMP) OBD Engine Codes

The fastest way to check the crank and/or camshaft sensors, on a 1995 or newer vehicle with OBD-II.

Just, plug in your scan tool, and check for any fault codes:

P0335….Crankshaft Position Sensors A Circuit
P0336….Crankshaft Position Sensor A Circuit Range/Performance
P0337….Crankshaft Position Sensor A Circuit Low Input
P0338….Crankshaft Position Sensor A Circuit High Input
P0339….Crankshaft Position Sensor A Circuit Intermittent
P0340….Camshaft Position Sensor ‘A’ Circuit (Bank 1 or Single Sensor)
P0341….Camshaft Position Sensor ‘A’ Circuit Range/Performance (Bank 1)
P0342….Camshaft Position Sensor ‘A’ Circuit Low Input (Bank 1)
P0343….Camshaft Position Sensor ‘A’ Circuit High Input (Bank 1)
P0344….Camshaft Position Sensor ‘A’ Circuit Intermittent (Bank 1)
P0345….Camshaft Position Sensor ‘A’ Circuit (Bank 2)
P0346….Camshaft Position Sensor ‘A’ Circuit Range/Performance (Bank 2)
P0347….Camshaft Position Sensor ‘A’ Circuit Low Input (Bank 2)
P0348….Camshaft Position Sensor ‘A’ Circuit High Input (Bank 2)
P0349….Camshaft Position Sensor ‘A’ Circuit Intermittent (Bank 2)

You can also use your scan tool to check for the presence of a cranking (rpm) signal. If an engine is cranking but is not starting because there is no spark. (it is often a clue that the crankshaft position sensor is not working).

In addition, Crankshaft Camshaft Position sensors, on pre OBD-II vehicles, you can use a scan tool to check for codes. Or use a manual flash code procedure to read out codes.

On a pre OBD-II GM application, a trouble Code 12 while cranking. Would indicate no reference signal being generated.
On pre OBD-II Ford applications, a Code 14, would indicate a problem with the crank position sensor signal. Ford calls this a “PIP” (Profile Ignition Pick-up) signal.

Conclusion

So, as you can see the most important sensors of any engine are, the crankshaft and camshaft position sensors. Finally, the crankshaft position sensors monitor as, a multifunctional sensor. And, is used to set ignition timing, detect engine (RPM) and relative engine speed.

As a result, , this sensor negates the need for, manual distributor timing. Consequently, the (CMP) sensor is used, to determine which cylinder is firing. And, to synchronize the fuel injector, and coil firing sequence.

BY DANNY BENDER