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For those who think: TL;DR long story short: I want to measure the voltage output at certain temperature but do not get a signal.

Details:

I have a BOSCH MAP Sensor here (0281006108), it has 4 Pins:

  1. GND
  2. Temperature
  3. 5V
  4. Pressure

(confirmed)

I am not sure if the sensor delivers correct data and I am by nature a person interested in details so I wanted to compare it to a new sensor. As I cannot do this in a controlled test in a car I decided to make my own test setup.

I wired the sensor according to spec and used an Arduino to record the data. On the pressure line (4) I get information and it does change if I change the pressure but on the temperature I get NOTHING!

I suspected the arduino so I used a 5Volt external Power Supply but again Nothing with a multimeter. Then I went back into the car and plugged the sensor back in place, added some more wires in between the plug and the sensor and voila, the car did the trick. But this doesn't help me.

So why on earth does it not work in my test setup but in the car? From what I know 0281006108 is an analogue sensor and the ECU doesn't send any data to the sensor.

Any help appreciated.

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  • 1
    What kind of measurement are you expecting? Most temperature sensors use resistance to get results, not voltage. If you are trying to measure voltage, you probably won't get anything. The easiest way to measure this would be by using an ohmmeter or a digital multimeter with an ohm setting. Just looking it up, I'm not sure of what the readings would be, but usually resistance increases as temperature goes up. It would be very noticeable, though the variance usually isn't that high (reading from one temperature to another will not produce a huge resistance movement).
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 11, 2016 at 14:31
  • In the car I got a voltage, it is the result of the input 5V and the resistance. The range is 2.4V at 27° to almost 0.9 at 70° (so far in the car)
    – AnyOneElse
    Commented Sep 11, 2016 at 14:36
  • 1
    I'm not an electronics guru, but if a resistance is introduced, isn't the source voltage changed due to the resistance, therefore giving something to read? More resistance causing less voltage?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 11, 2016 at 14:46
  • 1
    That sounds right to me. Most automotive applications use a "NTC" (negative temperature coeficient) sensor, which reduces resistance (and therfore voltage drop) as the temperature increases.
    – SteveRacer
    Commented Sep 11, 2016 at 15:09
  • and this is just the point... I get ZERO voltage. Which is really unlikely, but I assume there must be something I missed.
    – AnyOneElse
    Commented Sep 11, 2016 at 18:06

1 Answer 1

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Here is what I missed:

The Sensor is NTC as mentioned. Only the pressure sensing bit (piezo?) is the one using 5V. In fact from what I figured the resistor requires a voltage divider which is internally handled by the ECU. Measuring a resistance at PINs 1 and 2 I get 1.86kOhm at ambient temperature so the sensor does work but requires a different setup than I provided.

So if anyone comes across a similar issue: unless it is a thermocouple, it most likely requires a divider...

Here's some more information on the topic: http://www.circuitbasics.com/arduino-ohm-meter/

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