How to measure a Bosch LSU 4.9 wideband lambda sensor

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How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby KimAndersen » Sun Sep 07, 2014 7:38 pm

How to measure a Bosch LSU 4.9 wideband lambda sensor nominal pump current (Ip) without buying those expensive current clamp, such as the K110 MicroProbe.

This case study is different than others in that way it has no fault, so it's rather a study of how the Bosch Wideband LSU 4.9 sensor is working, when there is no Diagnostic trouble codes present in the ECU and the car are in perfect condition.

Before I move on with this case study I would like point out that the measurement off the wideband sensor are based on the documentation datasheet from Bosch LSU 4.9 and other reliable sources, which I have gathered around this subject.

The car in this case study is Volkswagen Jetta 2.0 TDI (Pumpe Duse) equipped with diesel partikel filter and with a Bosch Wideband sensor LSU 4.9 mounted between the turbo and the DPF. The engine code is (BMM) which is a 103 kw engine with 8 valves and the odometer is showing 130.000 km.

Let me start by showing the schematic diagram of a bosch wideband sensor connected to a ECU, which is shown as AWS.

BOSCH_LSU49_SCHEMATIC.jpg


AWS represent the hardware in the ECU, also known as a CJ125 IC chip which is vital for correct operation of the sensor, without this chip would the sensor not function at all.

My approach to measure the pump current from a bosch wideband LSU 4.9, is to measure the voltage drop over a known resistor. When we look at the schematic diagram is there one particular resistor inside the ECU that measure the pump current (IP meas.) and that resistor has a resistance value of 61.9 ohm.

But before we attach our Pico probes to sensor, we must first convert the voltage drop into milli amps by making a lookup table in Picoscope. The voltage drop over that resistor range from -124 mV (lambda 0.650) to around 139.5 mV (lambda 10.119).

To make the lookup table you need exact datasheet specification from Bosch LSU 4.9 and then you need to use ohm's law to make the conversion from milli volt to milli amps.

This picture represent the lookup table that I use to make the measurement from the wideband sensor. One thing to remember with respect to this lookup table is, that it can only be used at a Bosch LSU 4.9 wideband sensor.

BOSCH_LSU49_LOOKUP_TABLE.jpg
BOSCH_LSU49_LOOKUP_TABLE.jpg (42.24 KiB) Viewed 8731 times


Now that the Picoscope are set up for measurement of the wideband sensor was I becoming a little curious about this measurement whether it would function or not.

As always when we are dealing with a wideband sensor - it needs to be fully warm up. I drove a long trip to be sure that the engine was completely warm.

When I came back from my trip - I connect my measuring probe as follows - red probe to terminal Pin1 (Pumping Current) and the black probe to terminal Pin 5 (Trim Current) of the sensor.

To be complete frank I didn't know what to expect of this voltage measurement - would it functions or not !!!.With a warm engine and a idle speed at 900 rpm, it showed a reading of zero amps. Zero amps in respect to air/fuel ratio is perfect lambda 1.

The next test, was to conduct wide open throttle test (WOT). I forgot that - its a diesel engine and its restricted to 3000 RPM, at standstill.

My objective was, to see if there were any fuel correction taking place. To my surprise were there no fuel enrichment at all - it stayed at zero amps which means it must be in some sort of open loop.

I then began, to question this method of measuring pump current on a wideband sensor or perhaps I have done something wrong at my lookup table !!!.

As I'm not in possession any kind of documentation that explains in depth how volkswagen controls this wideband sensor. I have lots of information from volkswagen own SSP study files which i dont think cover this subject well enough.

It´s not easy, when you don't know the exact strategy of the ECU - what should one expect in terms of open/closed loop operation !!!

In my search for some answers to the missing fuel correction i decided to cruise the engine at 2000 rpm for about 5 minutes to see if i could get any response from the sensor. Then, at last the sensor became active and this was despite the engine was fully warm.

Every time you switch the ignition off and then on again it follows the same heat up strategy so be patient when you make this measurement.

This picture shows when the wideband sensor becomes active.

BOSCH_WIDEBAND_LSU49_ACTIVE.jpg



Now that the wideband sensor has become active it's a lot more fun to watch what is going on with those values i'm getting. There were a point, where i thought it was totally dead, but then again there were no diagnostic trouble codes present, so it could not be the whole truth i was witness to.

One thing that got me off course with respect to interpretation of those waveforms was, when i accidentally made a DTC P2238, which translated means (Short circuit between pump current Pin 1 and GND).

It happened when i was looking for the missing signal or should i say the correct signal - with the red picoscope probe connected to pin 1 (Pump Current Signal IP) on the wideband sensor and the other black probe on battery ground. As i remembered it goes the wideband sensor in permanent rich air/fuel ratio mode and i became confused.

BOSCH_WIDEBAND_LSU49_RESTRICTED_WOT_3000RPM.jpg


BOSCH_WIDEBAND_LSU49_LONG_WOT_TEST.jpg


With this case study i have only scratched the surface of what's possible to measure at a wideband sensor, but its a start for those people there just want to measure the pump current from this sensor.

Bear with me, i dont understand all the aspect or strategies that ECU are using, but i would like know it.

I hope this case study will be of some help to you out there under the bonnet.

Regards
Kim

BOSCH_WIDEBAND_LSU49_RESTRICTED_WOT_3000RPM.psdata
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BOSCH_WIDEBAND_LSU49_LONG_WOT_TEST.psdata
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BOSCH_WIDEBAND_LSU49_ACTIVE.psdata
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Bosch Wideband LSU 4.9 - Pump Current.psprobe
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby Steve Smith » Tue Sep 09, 2014 7:33 am

Hello Kim and thank you.

The time you have spent not only testing the vehicle but writing and presenting this post will no doubt assist and support 1000's of technicians who browse the forum every day.

I have taken all the information you have provided and hope to carry out a similar test on such a vehicle to improve my own knowledge base of broadband sensor activity when installed to diesel engines

I have only ever looked at feedback data provided by scan tools when reviewing diesel broad band sensor activity and I have to say it always appeared remarkably inactive!

Testing the sensor in parallel (using the scope) has revealed so much more.

Thank you once again, it is much appreciated

Take care........Steve
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby Robski » Tue Sep 09, 2014 3:37 pm

First let me get your attention to this

tiepie-automotive.com/en/Measurement_examples/Sensors/Oxygen_Sensor_Broadband

The resistor can be measured at the harness connector as described in the link, this is all well & good BUT it is another thing having the precise datasheet of what the sensor works at to create a look up table, this is all time consuming (for the first time).
It is far easier to use scan data for wideband O2's IMO, if I were having to diagnose enough then I would purchase the micro amps clamp, I can't remember the last time I had to look at a diesel wideband O2 if at all (?) & if mixture was an issue then an A/F sensor in it's place to verify the actual ratio.

I would have to ask why this particular sensor & fuel type was chosen for this write up, was it because the information was easy to find, as it's far more popular to have to diagnose a petrol wideband O2 ?

Good effort though all the same.
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby KimAndersen » Tue Sep 09, 2014 7:47 pm

Hi Robski

I haven't come across that website before you mentioned it. As i see this well documented website is it more a general thing, regarding measuring the wideband sensor pump current as a whole. My case study is more specific study of the Bosch LSU 4.9 wideband sensor, though it´s the same approach we are using in both cases.

There are multiple answers to that question. I wouldn't say it's easy to make a case study about a wideband sensor in a diesel engine, contrary i was surprised how little information there is to find on the "whole wide web". Most of the documentation found on the internet regarding diagnosis of a wideband sensor are made with a Eobd scanner or a DMM and thats the way the vast majority does it.

I like to see the whole picture and that is only possible with a oscilloscope where against when you are using a obd scanner you are only seeing calculated values, which in most cases are enough to diagnose a problem, but in the hard cases you simply would not get any usefull information to make a correct diagnose on.

I would agree with you in that the micro amp clamp is the right choice if you are using it frequently. I just wanted to show it possible to measure small current signals, without the use of a expensive equipment.

One thing to remember about the Bosch LSU 4.9 Wideband sensor is, that it is used a lot of different cars including petrol cars. This sensor are for both diesel and petrol.

I can only encourage people to make some waveform captures of this sensor, whether its a petrol or diesel and then let us interpret those in this forum.

There are so much to be learned about this sensor yet.

Regards
Kim
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby Robski » Tue Sep 09, 2014 8:21 pm

My case study is more specific study of the Bosch LSU 4.9 wideband sensor, though it´s the same approach we are using in both cases.

Yes I'm aware of that.

There are multiple answers to that question. I wouldn't say it's easy to make a case study about a wideband sensor in a diesel engine, contrary i was surprised how little information there is to find on the "whole wide web". Most of the documentation found on the internet regarding diagnosis of a wideband sensor are made with a Eobd scanner or a DMM and that's the way the vast majority does it.

Correct, that kind of info from the net is hard work, so do you think the majority of people will be able to source the datasheets ?
I also never said it was 'easy' to make a case study for a diesel wideband O2, I asked you if that particular sensor was easy to find the information on.

I like to see the whole picture and that is only possible with a oscilloscope where against when you are using a obd scanner you are only seeing calculated values, which in most cases are enough to diagnose a problem, but in the hard cases you simply would not get any useful information to make a correct diagnose on.

As do I BUT time has a factor, for example finding the correct info, double checking it's the correct info then calculating the values via ohms law & creating a look up table to suit etc etc.

I can only encourage people to make some waveform captures of this sensor, whether its a petrol or diesel and then let us interpret those in this forum.

There are so much to be learned about this sensor yet.

Let's sit back & see who follows your encouragement it would be interesting..........

Can I ask what's to be learnt about this sensor yet ?? Apart from how it performs from vehicle to vehicle under different fueling conditions as it's the same sensor, same voltages & same current spectrum, & same resistor with the CJ125 is it not ?
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby KimAndersen » Wed Sep 10, 2014 8:27 pm

Robski wrote:
My case study is more specific study of the Bosch LSU 4.9 wideband sensor, though it´s the same approach we are using in both cases.

Yes I'm aware of that.

There are multiple answers to that question. I wouldn't say it's easy to make a case study about a wideband sensor in a diesel engine, contrary i was surprised how little information there is to find on the "whole wide web". Most of the documentation found on the internet regarding diagnosis of a wideband sensor are made with a Eobd scanner or a DMM and that's the way the vast majority does it.

Correct, that kind of info from the net is hard work, so do you think the majority of people will be able to source the datasheets ?

The datasheet over the Bosch LSU 4.9 wideband sensor can be found on one of the many Bosch websites there are. But if you are looking after in depth documentation about this sensor, it can be hard to find such info.


I also never said it was 'easy' to make a case study for a diesel wideband O2, I asked you if that particular sensor was easy to find the information on.

I like to see the whole picture and that is only possible with a oscilloscope where against when you are using a obd scanner you are only seeing calculated values, which in most cases are enough to diagnose a problem, but in the hard cases you simply would not get any useful information to make a correct diagnose on.

As do I BUT time has a factor, for example finding the correct info, double checking it's the correct info then calculating the values via ohms law & creating a look up table to suit etc etc.

I can only encourage people to make some waveform captures of this sensor, whether its a petrol or diesel and then let us interpret those in this forum.

There are so much to be learned about this sensor yet.

Let's sit back & see who follows your encouragement it would be interesting..........

Can I ask what's to be learnt about this sensor yet ?? Apart from how it performs from vehicle to vehicle under different fueling conditions as it's the same sensor, same voltages & same current spectrum, & same resistor with the CJ125 is it not ?


There are the heat-up phase of the sensor and the measuring of the internal temperature which is a important part of controlling this sensor.

This is only seen from the wideband sensor point of view and then there are the car manufacturers different use of multiple ecu strategies to interact with this sensor which makes it hard to say precise how a wideband should behave under other terms and condition.

These two topics i here mention are maybe not the first everyone should start to study, but it is vital to know later on in the process in diagnosing this wideband sensor.

Yes you're right regarding to the measuring of the voltage/current as well as the internal resistor in the CJ125 chip, but when we are talking about the built-in resistor in the wideband sensor its self are there different resistors - this car had a resistance of 106 Ohm.


Regards
Kim
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby Robski » Wed Sep 10, 2014 9:41 pm

but when we are talking about the built-in resistor in the wideband sensor its self are there different resistors - this car had a resistance of 106 Ohm.


There's no mention of the 'trimming resistor' in your write up ?

There are the heat-up phase of the sensor and the measuring of the internal temperature which is a important part of controlling this sensor


How's this going to be measured ?
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby AuthorMike » Thu Sep 11, 2014 7:22 am

Robski wrote:First let me get your attention to this

tiepie-automotive.com/en/Measurement_examples/Sensors/Oxygen_Sensor_Broadband


We also have a very good thread on this exact topic on our forum ;) :

https://www.picoauto.com/support/topic10207.html
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby KimAndersen » Fri Sep 12, 2014 2:36 pm

Hi Robski

There's no mention of the 'trimming resistor' in your write up ?


No i haven't mentioned the trimmings resistor inside the wideband sensor because it´s not used to calculate the wideband sensor pump current flow.

Look at the first picture in this case study and you will see, there are a "measuring resistor" inside the CJ 125 chip - this resistor are used in the lookup table.

In the datasheet of Bosch wideband sensor LSU 4.9 are there referred to " IP meas" which is the wideband sensor pump current flow tabel.

How's this going to be measured ?


The heat-up phase of the wideband sensor can be measured with current clamp, this is not hard.In regards to the measuring of internal temperature in the wideband sensor is done as a simple voltage reading with the picoscope.

General when we are speaking about a measuring different voltages on components in a car with oscilloscope or DMM is not that difficult, what in my opinion are the difficult part of a correct diagnosis is the interpretations of the waveforms and to understand the logics and the strategies that the ecu are using in making the right decision.

Regards
Kim
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Re: How to measure a Bosch LSU 4.9 wideband lambda sensor

Postby Robski » Fri Sep 12, 2014 6:31 pm

No i haven't mentioned the trimmings resistor inside the wideband sensor because it´s not used to calculate the wideband sensor pump current flow

but when we are talking about the built-in resistor in the wideband sensor its self are there different resistors - this car had a resistance of 106 Ohm

Look at the first picture in this case study and you will see, there are a "measuring resistor" inside the CJ 125 chip - this resistor are used in the lookup table.



Kim,

I can see & read at the same time so there is no great need in telling me to look at the diagram which you got from a data sheet.

The heat-up phase of the wideband sensor can be measured with current clamp, this is not hard.

I am also aware of how to measure the 'heater' circuit current.

In regards to the measuring of internal temperature in the wideband sensor is done as a simple voltage reading with the picoscope.

Simple yes if the information is available.

I am going to leave it here as you don't seem to understand what I have typed, I am finding what you're typing a little contradictory as I have pointed out in the first quotes of this reply, I am also having to read your replies more than once to try get an understanding of what you're trying to say...............BUT this's is what you get with multi-national forums unfortunately.
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