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4 pin digital brake vacuum sensor - how does it work ?
4 pin digital brake vacuum sensor - how does it work ?
have a permanent dtc on a Mercedes C205 - 'check component brake vacuum sensor'. Clear the dtc and it comes straight back without starting engine.
I've scoped it, there is power going to it at all times, even with ignition off.
5v power and ground on pin 1 and 2.
pins 3 and 4 show frequency. The frequency only changes on one of the pins. It remains constant on the other. Could this be the problem ?
What is confusing me is when graphing the sensor on the scan tool the sensor seems to behave perfectly !
hope someone can help.....
thanks
I've scoped it, there is power going to it at all times, even with ignition off.
5v power and ground on pin 1 and 2.
pins 3 and 4 show frequency. The frequency only changes on one of the pins. It remains constant on the other. Could this be the problem ?
What is confusing me is when graphing the sensor on the scan tool the sensor seems to behave perfectly !
hope someone can help.....
thanks
Re: 4 pin digital brake vacuum sensor - how does it work ?
Hello,
I was really interested about this topic, have never really given two thougts about the whole sensor, other than it excists and gives a value to the ESP-control unit.
I looked up a wiring diagram from a MY2020 W205 and compered it to a MY2024 W447 Vito.
In the case of Vito there are two variants with the OM654 diesel it has a 3-wire Sensor B150 and with the M256 Petrol engine it has a 4- wire B150/3 sensor
I did not have the chance to scope a 4-wire variant but there was a brand new Vito with the 3-wire sensor and it uses a 12tick SENT protocol to transfer the data to ESP
I decoded it as a SENT FAST 12 tick and A5. Pressure (12bit + 12bit)
When the decoder was running, I did a simple function test, let the engine idle and build up maximum vacuum pumped the brake pedal 10 times and the let the vacuum build up again.
Took the SENT data from this test to excel and graphed it
Its clear that both channels send data regarding the vacuum only in mirror image of each other.
The 4-wire B150/3 on the petrol variant has a name of a double-vacuum sensor in the wiring diagram so there is a possibility that both SENT lines work in the same way and this type of excel graph would be one way to test that all sensor channels are working properly, if one channel is working and the other is not, it can still show values via the scan tool.
Other good way know if these SENT sensors are working correclty is reading the fault codes in the Slow SENT
message
From what I have gathered from the internet is that the ASIC circuit in the sensor does the actual fault detecting and sends it to the control unit via the SENT bus. The actual control unit usually displays fault code descriptions like ” control unit has receved information that sensor is not functioning properly”
A while ago I found an interesting document from Bosch Rexroth SENT sensor that has some good general information about how SENT decimal values have certain limits that trigger fault codes
Found the whole thing on google so I will put a link on to the document.
https://www.hydba.com/wp-content/upload ... exroth.pdf
The fault codes in SENT slow seem to be manufacturer specific so they dont give much more information but the key thing to a technician is to see that is there any fault code or not
for example i had a differential pressure sensor that had a CH1 malfunction
And after swapping a new sensor it showed no faults
Sorry for the long(ish) answer to your question, I basically threw up everything I know about the SENT but hopefully there was some useful things in the mix
Especially the looking up fault codes from the SENT slow message takes some of the quess work out of the diagnosis.
Best Regards,
Jarkko
I was really interested about this topic, have never really given two thougts about the whole sensor, other than it excists and gives a value to the ESP-control unit.
I looked up a wiring diagram from a MY2020 W205 and compered it to a MY2024 W447 Vito.
In the case of Vito there are two variants with the OM654 diesel it has a 3-wire Sensor B150 and with the M256 Petrol engine it has a 4- wire B150/3 sensor
I did not have the chance to scope a 4-wire variant but there was a brand new Vito with the 3-wire sensor and it uses a 12tick SENT protocol to transfer the data to ESP
I decoded it as a SENT FAST 12 tick and A5. Pressure (12bit + 12bit)
When the decoder was running, I did a simple function test, let the engine idle and build up maximum vacuum pumped the brake pedal 10 times and the let the vacuum build up again.
Took the SENT data from this test to excel and graphed it
Its clear that both channels send data regarding the vacuum only in mirror image of each other.
The 4-wire B150/3 on the petrol variant has a name of a double-vacuum sensor in the wiring diagram so there is a possibility that both SENT lines work in the same way and this type of excel graph would be one way to test that all sensor channels are working properly, if one channel is working and the other is not, it can still show values via the scan tool.
Other good way know if these SENT sensors are working correclty is reading the fault codes in the Slow SENT
message
A while ago I found an interesting document from Bosch Rexroth SENT sensor that has some good general information about how SENT decimal values have certain limits that trigger fault codes
https://www.hydba.com/wp-content/upload ... exroth.pdf
The fault codes in SENT slow seem to be manufacturer specific so they dont give much more information but the key thing to a technician is to see that is there any fault code or not
for example i had a differential pressure sensor that had a CH1 malfunction
And after swapping a new sensor it showed no faults
Sorry for the long(ish) answer to your question, I basically threw up everything I know about the SENT but hopefully there was some useful things in the mix
Especially the looking up fault codes from the SENT slow message takes some of the quess work out of the diagnosis.Best Regards,
Jarkko