Two months ago my Chevrolet Aveo 2007 had intermittent interior and exterior light flickering problem that was especially noticeable while idling or driving at low speeds. Also, one morning the car had to be jumpstarted due to low battery. I also noticed strange ~1 Volt drop over battery terminal and the clamp connecting to it (there is remote possibility I may have misused multimeter, but I doubt about it). So, instead of assuming alternator or battery issues, I decided first to clean and e-grease connections to the battery terminals and, surprisingly, the issue went away.

However, after two months my car simply stalled after driving first 20 meters. This time there was no interior or exterior light flickering. There were no status lights in the dashboard (e.g. the red battery light indicating starter issues). So, I checked the codes with OBD2 reader and they were:

  • P0340: Camshaft Position Sensor Circuit Malfunction
  • P2106: Throttle Actuator Control System Forced Limited Power
  • P2110: Throttle Actuator Control System Forced Limited RPM
  • P2101: Throttle Actuator Control Motor Circuit Range/Performance

When I try to start the car I see that starter engages and the belt spins as expected, but the car still won't start.

Also the battery voltage drop this time between + and - at the time when starter spins is 12.5V to 10.8V (without Nekteck jumpstarter assist) and 12.03V to 11V (with Nekteck jump start assist). This is the first time I am using portable battery jump start assist so I haven't verified if it actually works.

Now I am trying to make sense out of all of this:

  1. Is the issue this time with something else like Camshaft Position Sensor? Is there an easy way to know if it is good or bad?
  2. Is the issues with starter/alternator again showing up and possibly causing the P0340 code due to weak starter? How to know if alternator is good or bad?


Here is picture of my camshaft sensor with its connector unplugged. I suppose there should be 5V square wave with oscilloscope (or 2.5v with multimeter) between orange and black wire? Is the easiest way to probe for that voltage simply by splicing the cables or shall I intercept somewhere else?

enter image description here


Below is how I wired up everything. At the time of cranking the voltage between yellow and black wire jumped from 1.2V to 1.4V. Note, that I have a cheap multimeter and I am not sure if it is able to properly measure voltage for non-sinusodial wave functions.

enter image description here


So this how the sensor output looks like on oscilloscope. Obviously, don't look like nice square waves:

enter image description here

Update4 I changed the camshaft position sensor and the P0340 code disappeared, but the car still does not crank up. The voltage drop at the time of cranking now is from 12.0V to 10.8V.

2 Answers 2


Is the issue this time with something else like Camshaft Position Sensor? Is there an easy way to know if it is good or bad?

Yes, a p0340 code can cause a no start as the PCM uses the CMP sensor for fuel injection. If you want to check the sensor backprobe the output and check for a 5v square wave with a scope or roughly 2.5v while cranking with a multimeter. You need good ignition voltage and ground as well. I think you can look at CMP active counts with a Enhanced OBD2 scantool.

Is the issues with starter/alternator again showing up and possibly causing the P0340 code due to weak starter? How to know if alternator is good or bad?

Neither will cause a crank no-start unless the alt blew some fuses. That's excellent starter voltage drop. If you want to check the alternator get the engine spinning fast enough (e.g. running...) and check it's output voltage and amps. Then compare against spec.

  • 1) I guess CMP is another acronym for Camshaft Position Sensor? 2) Just to confirm, I guess you suspect that Powertrain Control Module is preventing fuel from getting to combustion chamber? Is there an easier way to verify this without scope? 3) I could get a scope, but where shall I put the probes? Thanks! Commented Sep 23, 2017 at 22:48
  • @HansSolo Yes CMP is camshaft position. CKP is crankshaft position. The PCM uses the CMP sensor for fuel injection timing. If it doesn't see a signal it won't fire the injectors. You could confirm this by looking for a fuel injector pulse at the injector connector. To backprobe you'd have to locate the CMP sensor it should be by the cam gears. Pin 3 is your output 1 & 2 are 5v Ref and Low Ref or ground. You slide a back probing pin or a sewing pin in through the back of the connector. Just be careful not to damage the weather pack seals.
    – Ben
    Commented Sep 23, 2017 at 22:53
  • I updated my question with a picture. Since I got 5V with my multimeter between black and gray wires, then I guess those are the GND and +5V. So orange one must be the sensor's output, right? Also, I guess I would have to splice the wires (ie remove wire isolation) to be able to connect to the sensor with a sewing needle or something as you mentioned? Commented Sep 23, 2017 at 23:47
  • " I guess I would have to splice the wires..." You are focusing on the wrong thing. Even if there is a 5V square wave there, nothing will happen unless the engine control unit is getting that signal and interpreting it correctly. The fault might not be the actual sensor. Poking sewing needles into the cables is a waste of time, and will leave holes in the wiring insulation for water to get in and letting corrosion start from the inside where you can't see it. If you want to "test the cable", unplug the connector(s) and use the connector pins and sockets as test points.
    – alephzero
    Commented Sep 24, 2017 at 0:09
  • @HansSolo no need to strip insulation. you get at the backside of the connector and slide a pin in there that allows you to measure the voltage. you need to be careful with probing connectors damage to the weather pack seals can let moisture in. And probing from the front carries the risk of spreading terminals.
    – Ben
    Commented Sep 24, 2017 at 0:14

These faults are most likely caused by one problem.

If the engine ECU is the Siemens/Simtec model I wouldn't go any further and would send the ECU away for testing and repair. These ECUs are notorious for multiple faults but the most common is for one or more of the 5v reference circuits to fail. These would give the symptoms you have. Changing the crank sensor may just be a coincidence or it was a separate fault. (It will be the Siemens ECU if the connectors come from the top of the ecu and usually it is bolted to the intake manifold).

It could be as simple as a flat battery, anything lower than 12.6v with no load indicates a low battery. Put a known good battery onto the vehicle, fitted properly without jump leads.

The P2110 doesn't indicate a fault with the throttle actuator, it actually means the ECU is reducing the movement of the throttle thus reducing the engines power. Basically it is a complicated way of saying the vehicle is in Limp Home Mode.

P2106 is similar to P2110 and P2101 is a by-product of the two, the throttle output value is out of range due to being restricted by the ECU.

To eliminate the cam sensor completely I would do the following:

To probe the pins I would recommend back probing, the way you have done it leaves too many variables and places for errors to occur, if you can't get proper back probes designed for the job you can use normal sewing needles/pins and push them down the rubber seals in the plug and hook your crocodile clips to them.

  • Check the ground of the cam sensor - With the sensor connected as usual, Put the meter in voltage mode and put the leads between the sensor ground and the battery negative terminal. Anything more than a volt indicates a bad ground.

  • Check the 5v feed to the cam sensor - Same as above but put the meter leads between the sensor 5v pin to the corresponding pin on the engine ECU. Anything more than a volt indicates a wiring fault.

  • Scope the sensor output, hook the scope ground to the batteries negative terminal and the scopes input to the sensor output. Have the scope set to around 20mS per division. Google image cam sensor reference waveform. Although I don't think the scope in the photos you attached has enough resolution to properly diagnose a fault. (There's a reason automotive oscilloscopes can cost multiple thousands)

Also physically check that the camshaft is turning, you may be able to see it through the oil filler or you may have to remove a cover. Check while someone else turns the engine over. Although P0340 indicates a circuit fault its not uncommon for certain ecus to confuse a plausibility and circuit fault.

  • The p340 and other codes mysteriously disappeared, but car still does not start. Yes, the timing belt is moving (to access the sensor I had to remove the upper cover and see that timing belt markings are in different place after each crank attempt). Also what kind of errors are you referring to because of me intercepting with oscilloscope just with alligators? Commented Oct 7, 2017 at 21:11
  • Does it have the ecu I mentioned? Commented Oct 7, 2017 at 21:12
  • Can you tell me how can I check that - the ECU did not seem to have any brand names on it written. Though this is Chevrolet Aveo (American car made by Koreans). So my guess would be that the ECU is made by Koreans/Daewoo and not Germans/Siemens. Commented Oct 7, 2017 at 21:32
  • The voltage between battery minus and 1) sensor gray wire is good 5V, 2) sensor black wire is 3mV, 3) sensor orange wire is growing from 2V to 12.2V (without cranking, but key ON) Commented Oct 8, 2017 at 1:38
  • Is the ecu bolted to the intake manifold? It will be either a Bosch or Siemens unit Commented Oct 8, 2017 at 20:41

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