I have taken out this camshaft position sensor out of my Chevrolet Aveo 2007 and I am trying to verify whether the issue I am facing is with the sensor or the ECU/computer (the car cranks, but does not start and had P0340 code).

My question is - how do I wire up this camshaft position sensor in lab environment (without car in the picture) to verify that it is working according to its specification?

Additional info:

The harness that plugs into sensor has 3 wires (Pink, Black, Black&Blue). When I turn car key to ON position with harness unplugged from sensor, then

  1. voltage between Battery Minus and Pink Wire slowly grows from 2V to 12.2V over 10 second period;
  2. voltage between Battery Minus and Black Wire stays at 0V;
  3. voltage between Battery Minus and Black&Blue Wire stays constant at 5V.

With sensor plugged into car's harness and intercepting with oscilloscope between Black Wire and Pink Wire at the time of Cranking I see that 12.2V voltage disappears and there are "squarish" pulses that don't have steep triggering edge with lows of 0V and peaks at only ~2.5V:

Voltage between pink and black wire when cranking

Here is schematic from my car (BK - black, PK - pink, L-BU/BK- Blue&Black wire): Schematic

I guess this is confusing me because this sensor does not have a simple Output pin where ADC in car's ECU measures voltage. I am not sure:

  1. which electrical property (current, voltage) is supposed to change on which wire when camshaft position sensor detects tooth on reluctor ring.
  2. why voltage on Pink wire slowly grows from 2V to 12V. And when I crank, then oscilloscope shows waves of 2.5V peaks between Black and Pink wire. Was it supposed to be constant at 12V?
  3. W.R.T. #2 as test would it be safe to connect Battery Plus to sensors pin where Pink wire previously went in to eliminate problem of voltage slowly rising to 12V?

After adding 10KOhm sensor, as suggested in one of the answers by JRE, I see that rising edges in the oscilloscope are now steep. This probably proves that problem in my case is not with the sensor, but rather somewhere else in my car's electrical wiring.

After connecting as JRE suggested

  • \$\begingroup\$ It would be easier to test the sensor on the vehicle. One wire should be a voltage source for the sensor, another should be sensor ground, and the third should be a digital signal to the ECM. \$\endgroup\$ – LsD Oct 11 '17 at 17:40
  • \$\begingroup\$ I tested sensor on vehicle already and got those ugly squarish waves in the oscilloscope picture. Also, the voltage on Pink wire was mysteriously growing from 2V to 12V over 10 second period when I turned key to "ON", but did not crank. I don't know whether that is expected or whether that already indicates another issue. I removed the IGN1 fuse and the voltage still grew to 12V on PINK wire. That is the reason why I want to test sensor outside the car to see how square waves are supposed to look like. Why would it be hard to test it outside vehicle? I have power supply and few spare resistors \$\endgroup\$ – user389238 Oct 11 '17 at 17:57
  • \$\begingroup\$ The output is the blue/black wire - its the one that goes to the engine control module. If the sensor is supposed to indicate the camshaft position, and the signal on the blue/black wire doesn't change then the sensor is bad. \$\endgroup\$ – JRE Oct 12 '17 at 5:51
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    \$\begingroup\$ The output of the sensor is probably something like an open collector - it pulls down the 5V from the ECU. Did you really measure 2V on the pink wire? That is just wrong. The pink wire goes to the battery through a fuse. There should beva solid 12V on it. \$\endgroup\$ – JRE Oct 12 '17 at 18:43
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    \$\begingroup\$ If it isn't getting power then it can't work right. Check the wiring. Maybe there's a break in the pink wire or its connections. \$\endgroup\$ – JRE Oct 12 '17 at 19:14

Well, nobody else seems inclined to answer so I'll go a head and give it a shot.

This is a simplified diagram of your sensor taken from the schematic you posted:


simulate this circuit – Schematic created using CircuitLab

To test this on the work bench, you provide 12V on the pink wire and ground on the black wire. Then you need a 5Volt supply, with its ground connected to the ground of the 12V supply. Connect the 5V to the blue/black wire through a resistor - I'd probably start with a 10k Ohm resistor.

Connect the ground of your oscilloscope to the black wire, and the tip to the blue/black wire.

Now, move a metal object like a screwdriver or wrench around the sensor in the place where the camshaft would usually be. You should see some reaction on the scope when you move things around.

There's not a lot that can go wrong here.

The options are as follows:

  1. Bad wire. Check all of the wiring for continuity. Since you mention the 12V going from 2V to 12V slowly when you turn on the engine, there might be a problem with the 12V supply wiring.
  2. The sensor is bad. If the wiring is OK, then this is the most likely problem.
  3. ECU input is broken. This is the most expensive problem, since the only real solution is to replace the ECU.

Check the wiring and connectors carefully. If they are OK, replace the sensor. If that doesn't help, then the ECU is the only thing left.

| improve this answer | |
  • \$\begingroup\$ Thank you so much! I added the 10K Ohm resistor after 5V power supply as you suggested and and I am getting perfect 5V square waves with steep rising edges when I move metal object in front of the sensor. \$\endgroup\$ – user389238 Oct 15 '17 at 3:48

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