Dual tracing - Camshaft position sensor vs crankshaft position sensor

You will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this page.

How to perform the test

Channel A

Plug a BNC test lead into Channel A on the PicoScope. Fit a large black  clip on the test lead with the black moulding (negative) and a Back-pinning Probe onto the test lead with the coloured moulding (positive). Place the black clip on the battery negative terminal and probe the crankshaft position sensor's negative (or number 1) terminal with the Back-pinning Probe as illustrated in Figure. 1.

Alternatively connections can be made using the TA012 breakout lead. Connect the BNC test lead directly to the two shrouded plugs on the breakout lead. If a smaller-than-anticipated waveform is shown, try reversing the connections. Connection of the breakout lead is illustrated in Figure 1.

Channel B

Plug a BNC test lead into Channel B on the PicoScope. Place a large black clip on the test lead with the black moulding (negative) and a Back-pinning Probe onto the test lead with the coloured moulding (positive). Probe the outputs of the camshaft position sensor until the larger waveform is displayed, the smaller waveform being the earth return.

Alternatively the TA012 two-pin test lead adapter can be used, as illustrated in Figure 2.

With the example waveform displayed on the screen you can now hit the space bar to start looking at live readings.

Example waveform

Waveform notes

In this waveform we can observe the output voltage from the AC-excited Crank Angle Sensor (shown in blue) at the same time as monitoring the inductive Camshaft Position Sensor trace (shown in red). The main reason for evaluating these two waveforms together is to look for any unwanted offset in timing between the two sensors, which could indicate a slipped timing belt or a stretched timing chain.

Example fault

This waveform is taken on a longer timebase than the first waveform, so it shows several revolutions of the engine. It was also taken from a different engine, this time with a Hall-effect CPS. Ch B (red, upper) is a good AC-excited CKP waveform. Ch A (blue, lower) is the CPS waveform. It shows large positive spikes reaching +12 V in addition to the expected 0 to +4 V pulses from the camshaft position sensor. This probably indicates an intermittent short-circuit to +12 V.

Technical information

Please see individual waveform topics:

  • Camshaft position sensors (inductive)
  • Crankshaft position sensors (inductive)

AT151-2

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • 2 Pin AMP connector breakout lead

    £42.00

  • Back-pinning Probe Set

    £48.00

  • Flexible Back-pinning Probe

    £7.00

  • PicoScope Battery Clip

    £5.00

  • Large Dolphin/Gator Clips

    £10.00

  • Premium Test Lead: BNC to 4 mm, 3 m

    £48.00

  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)

    £179.00

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Guided test: Cam vs crank sensor.  Diagnose timing errors.