Focus intermittant no start CAN BUS

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Focus intermittant no start CAN BUS

Postby RYM6746 » Thu Mar 23, 2017 7:08 pm

Hi, Customer complaint is a " intermittent hard start" I go out to the vehicle and it starts straight up. I scan the whole car and there are U codes stored in the instrument cluster, ABS and engine ECU. I have seen this symptom a handful of times before and when the vehicle decides its not going to start the immobiliser light on the dash stays illuminated and normally a sharp whack on top of the cluster will extinguish the light and the vehicle will start. It is a common fault within the instrument cluster. I know a component in the cluster intermittently upsets the CAN network (I think) not allowing the immobiliser to work. I had some time to spare and thought I would scope the CAN network and see if I could spot any faults. I think you can see a faulty node in this capture but I am not 100% sure so I thought I would ask the experts on here for there opinion? I noticed the voltage changing between messages which is easy to see on capture 30. Is this the sign of a failing node or am I over analysing the waveform? All advice is welcome as I am still learning about CAN BUS
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Re: Focus intermittant no start CAN BUS

Postby STC » Thu Mar 23, 2017 10:51 pm

a sharp whack on top of the cluster will extinguish the light and the vehicle will start

So something changes when you whack it ? "What" is the million dollar question.

Some "things" can be affected by a wallop, some wont be !!


am I over analysing the waveform?


If it is the Common Issue then you need to either fit and code a new cluster or examine both sides of the PCB with a microscope.

A reflow is known to solve it more often than not.
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Re: Focus intermittant no start CAN BUS

Postby RYM6746 » Fri Mar 24, 2017 12:48 am

Yeah the previous ford focus's that have had these symptoms with the exact same fault codes stored. I have seen them intermittantly not start whilst they are at the garage. When they are in there no start state I have managed to start them by hitting the top of the cluster. I have then sent the cluster off for test and repair and everytime they have failed the test and been repaired and it has fixed the problem. So when this focus turns up with a customer complaining of a difficult start and I see what cluster is fitted and what fault codes are stored, I can be very confident that it is the same fault that I have previously experienced. On this occasion I have not seen the car in a no start state but I know from the previous cars and the fault codes stored that it effects the CAN BUS.
So the real reason for me being on here with this uploaded waveform is to ask the question.
1. From the waveform I have taken is it possible to see a failing node on the network even though the fault is not severe enough to stop the vehicle from starting?
2. Is the slight change in voltages on capture 30 possibly the cluster showing signs of failure or am I over analysing the waveform?
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Re: Focus intermittant no start CAN BUS

Postby victor2k » Fri Mar 24, 2017 7:25 am

Hello,
Try to make a new capture only if you can't diagnose your dashboard and the engine don't start.Maybe you will see a wrong signal from dashboard transceiver.Increasing the resistance(bad/broken soldering on PCB) will reduce the oscilation in voltage transition.
At 200 MS/s I think you over analyze the signals...
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Re: Focus intermittant no start CAN BUS

Postby RYM6746 » Fri Mar 24, 2017 10:14 am

Is the difference in voltage on capture 30 a problem or is it normal?????????????
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Re: Focus intermittant no start CAN BUS

Postby STC » Fri Mar 24, 2017 11:38 am

I would guess that the DTC's you have are for "Missing Messages" as opposed to "NO Communication"

If so, unless you are going to decipher the "messages" on the network and have "Known Good" of what should be there at any given time then scoping the CAN will not help.

If you can communicate with everything diagnostically then CAN is good ... Period. You have a component either not listening, talking or both. Possibly due to internal loss of power, ... .... ..... ......
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Re: Focus intermittant no start CAN BUS

Postby RYM6746 » Fri Mar 24, 2017 12:49 pm

Thanks for all your input but let me be clear just for kicks I thought that with the spare time that I had I would scope the CAN to see if it was possible to see the cluster starting to fail. I know that in the waveform I have uploaded that every thing is working as it should. But there ARE annomillys in that waveform that I have not seen in previous waveforms I have taken. I was hoping an expert on CAN could tell me that the difference in voltage or the spikes that are present are due to a failing resistor or something like that in one of the nodes (possibly the cluster)
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Re: Focus intermittant no start CAN BUS

Postby victor2k » Fri Mar 24, 2017 2:31 pm

RYM6746 wrote:Thanks for all your input but let me be clear just for kicks I thought that with the spare time that I had I would scope the CAN to see if it was possible to see the cluster starting to fail. I know that in the waveform I have uploaded that every thing is working as it should. But there ARE annomillys in that waveform that I have not seen in previous waveforms I have taken. I was hoping an expert on CAN could tell me that the difference in voltage or the spikes that are present are due to a failing resistor or something like that in one of the nodes (possibly the cluster)

Hello,
The difference in voltage isn't normal ,but the spikes can be created by a LC component of your measurement circuit.
According to TJA/PCA CAN transceivers datasheet(this is used in dashboard) the differential bus imput voltage can be in 1,5-3 v range but starting from frame 225 us you have only 2v!I think you must record CAN signals when engine not start to confirm this diagnostic based on voltage monitoring ...
My advice:if PCM and ABS will report trouble in comm with dash open this...5 minutes and a good microscope will give your answer.
You will not find a falling resistor on PCB but a increased resistences of traces from connector to CAN transceiver.
Regards
PS
1.I am not a CAN expert
2.Anyway 200 MS/s can detect extraterestrial inteligence or...some flies(please look at my untitled attach)?
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Re: Focus intermittant no start CAN BUS

Postby RYM6746 » Fri Mar 24, 2017 9:02 pm

Thanks for the reply some very good info. The sample rate was me accidently tapping on the sample nudge buttons thinking it was the capture page buttons. I remember doing it, now you have pointed it out. I wasn't paying attention at the time. I definitely didn't set it up on purpose to sample that fast. Thanks for pointing my mistake out though. What would I be looking for under the microscope a dry solder joint?
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Re: Focus intermittant no start CAN BUS

Postby RYM6746 » Fri Mar 24, 2017 9:11 pm

In this video at some point (I'm sorry I can't remember how far in it is) The knowledgeable chap says you can actually see the 120 ohm resistor failing on the signals they are capturing using the scope. I was hoping for some reason or another for my voltages being inconsistent. https://youtu.be/WdS-m5Xd4Jc
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