How to test camshaft position sensor with oscilloscope

An Introduction to Diagnostics

Table of Contents Show

An Introduction to Diagnostics
Customer Interview
OBD Diagnostics Fault Code
Replacement did not cure the fault
Using PicoScope Diagnostics
Cam / Crank Signal
Verification of the Repair
Professional Service for your Customers
PicoScope settings
Connecting PicoScope
How many ohms should a camshaft position sensor have?
How do I know if my camshaft sensor is good?

This article discusses how PicoScope Oscilloscope Diagnostics fits into the repair process.
Watch the animation (video) below.

Customer Interview

Let's start with an example:
A customer arrives at your workshop with an engine running issue. The first step is to ask the customer about the problem. A dashboard warning light (e.g. engine) often, but not always, alerts the customer to a problem requires attention.

OBD Diagnostics Fault Code

Your next step would probably be to attach a serial diagnostic or OBD tool to the vehicle.

You may see fault codes being returned, such as:

P0016: Crankshaft Position - Camshaft Position Correlation
P0345: Camshaft Position Sensor "A" Circuit; and
P2614: Camshaft Position Signal Output Circuit/Open

You might therefore assume that the most likely cause of these codes would be a faulty camshaft sensor.

Replacement did not cure the fault

The camshaft sensor was replaced, the fault code erased, and the vehicle returned to the owner. However, in this example, the customer returned the next day with the same fault.

Using PicoScope Diagnostics

The simplistic senario above is all-too-often true. Lets consider a workshop equipped with a PicoScope. The astute technician would connect a PicoScope to the camshaft sensor output to test it before replacing it. The technician might also connect another channel to the crankshaft sensor to compare the two signals. Oscilloscope Diagnostics provides you with a much clearer picture of what is happening.

Cam / Crank Signal

The red crankshaft signal (inductive sensor) clearly shows the missing tooth used to index the rotation. The blue camshaft repeats (in this case but not always, one pulse) every second revolution of the crank. So far, everything looks good - there seems to be valid crank and cam signals! What could be wrong?

The technician wiggles the wiring and notices that the canshaft signal drops-out intermittantly as he does so. It follows that it is a wiring fault and the camshaft sensor is actually fine. A quick inspection finds that chafing of the cam signal wire in the loom caused it to wear through and the technican was able to repair the fault easily and without replacing the good camshaft sensor.

The animation below shows the scenario.

This new series of videos features the brand new 4425A and 4225A PicoScope with PicoBNC+.

Verification of the Repair

Following the wiring repair, the test was repeated with a PicoScope. The scope showed a clear fix. The fault codes were erased and the vehicle was returned to the customer. The workshop was confident that the root cause had been found and fixed.

Professional Service for your Customers

The customer left the workshop, happy after a successful repair. With no fault recurrence, this professional diagnostic workshop ensured future business with their customer. This is of course just one example of where PicoScope fits in the diagnostic journey. As technicians, you will understand there are many tools at your disposal, including technical information, training, knowledge, serial diagnostic tools, gas analyzers, and of course your PicoScope.

To find out more about how PicoScope can benefit your workshop and business, please click Next.

The correct operation of the hall effect camshaft position sensor (CMP) is dependent upon the integrity of the CMP circuit (power, ground and signal wiring) the fitment of the CMP in relation to the pick-up, the air gap between the CMP and pick-up, and the correct installation and orientation of the Camshaft or pick-up ring.

The camshaft or pick-up ring should also be inspected for damaged teeth and excessive run-out.

The CMP will display operational characteristics that are inconsistent due to circuit faults, electromagnetic interference, mechanical failures or measurement and connection errors.

The results obtained are therefore symptoms of underlying conditions and not as a result of a faulty CMP.

In order to efficiently perform the test, you will need the TA125 premium test lead, TA158 black battery clip and PQ070 or PP943 universal breakout lead set.

PicoScope settings

The PicoScope should be on channel A, DC coupled and the input range of ± 20 V (alternative setting of ± 10 V for CMP with 5 V output signal).

The time base should be set at 20 ms/div (alternative setting 50 ms/div for additional camshaft rotations) and sample count one MS.

Using vehicle wiring diagrams, identify the signal wire of the CMP.

The hall effect CMP will generally utilise three wires, one of which carries the signal during engine running whilst the others carry a 5V or 12V power supply and a 0V ground reference.

Connecting PicoScope

Locate and disconnect the CMP multiplug before inserting three relevant universal breakout leads between the CMP and vehicle harness in order to complete the circuit.

Then, connect the blue TA125 test lead to channel A of the scope, connect the blue test lead to the breakout lead connected to the signal wire of the CMP.

The black ground lead will then need to be connected to the vehicle chassis or battery negative terminal using the black TA158 battery clip.

Example waveform at 20 ms/div.

When this has been completed, run your scope software by pressing either the space bar on your keyboard or the “go” button in PicoScope.

Crank and run the engine while monitoring the signal on channel A and then press the “go/stop” button in PicoScope to halt the capture and enable waveform analysis.

Diagnosis

Unlike the inductive style CMP the amplitude of the hall effect CMP signal remains fixed (regardless of engine speed), however the frequency of the signal will increase in direct proportion to engine speed.

The correct formation of the square wave signal is paramount to ensure efficient engine performance, each square pulse is generated by the movement of the camshaft pick-up passing the sensing tip of CMP.

Each pulse represents a single tooth, lug or drilling of the pick up which should therefore be uniform in structure, without deformation and identical in sequence.

Depending on manufacturer, numerous style pick-ups are utilised to denote one complete camshaft revolution.

For example, manufacturers may use one single pulse (a single lug) or multiple pulses denoting the precise camshaft position in relation to firing order, it is important to refer to the vehicle technical data.

Go to the PicoScope library for more guided tests and information by clicking ‘more details’ below.