All of a sudden my Punto 188 is cranking but not starting, not even a hint.
I was pointed out that mostly this may be due to a faulty crank or cam sensor.

Unplugged and removed these sensors and took readings with a multimeter at the connector side leading to ecu (refer to picture).
I did this to find the respective supply and ground pins of sensors (these are 3 pin sensors). In order for me to later test the sensors, I needed to know which are the ground and supply pins..

With key ignition switch in ON position, I got the those readings which do not look right to me for the crank sensor(top). I was expecting a 12v or 5v on one of the pins coming from the ecu supplying the sensor however there is only 1.5v on the red wire and 2.5v on the white wire!

Can someone shed some light on what is happening? Is there a problem with the ecu or what ?

Please help

Just a quick update.
I found out that the crank sensor lead was shorted. Somehow there was on oily reaction and the inside insulators melted from the inside. There is no sign of heat , the cable looked fine from the outside. Definitely this was a reaction of the insulation rubber with some sort of chemical as the insulation is very soft and can be scraped off with a finger!

Now the only thing I pray for is that the Ecu side is not damaged due to the shorted sensor. However I have serious doubts about this due to the low voltage it was supplying to the sensor when I checked it this morning.

Do you think that there is a good chance that the ecu is damaged at this point?
Is there any protection to the Ecu (fuse or some sort) that will protect ecu from damage if the output rail voltage is shorted ?
Can someone check what voltage reading should there be on the red and white wire of connector? This will confirm if Ecu is damaged or not.

Please help:worship:

leander said:

Just a quick update.
I found out that the crank sensor lead was shorted. Somehow there was on oily reaction and the inside insulators melted from the inside. There is no sign of heat , the cable looked fine from the outside. Definitely this was a reaction of the insulation rubber with some sort of chemical as the insulation is very soft and can be scraped off with a finger!

Now the only thing I pray for is that the Ecu side is not damaged due to the shorted sensor. However I have serious doubts about this due to the low voltage it was supplying to the sensor when I checked it this morning.

Do you think that there is a good chance that the ecu is damaged at this point?
Is there any protection to the Ecu (fuse or some sort) that will protect ecu from damage if the output rail voltage is shorted ?
Can someone check what voltage reading should there be on the red and white wire of connector? This will confirm if Ecu is damaged or not.

Click to expand...

The crank sensor and cam sensor use different technologies. The three wire crank sensor is a conductive sensor with an earth screen. Only the cam sensor needs a reference voltage for the hall effect sensor. If you repair the wiring and there is a fault in the ECU you are probably going to get a circuit malfunction code. The ECU can test the circuit for the expected behaviour.


Here is a thread with the same voltages you got where the crank sensor was not the problem.


https://www.fiatforum.com/punto-ii/464134-crank-no-start-no-spark-no-dtcs.html?p=4368675

Thanks Judderbar. I fixed the sensor lead and now the car starts without any problem. Yes the correct reading from the ECU to the crank sensor plug are 1.5v-2.5v-grd. Engine light flashed on startup however I did the phonic wheel learning proceedure(throttle up to 6000rpm for 3 times) and it went off !