Car diagnostics using an oscilloscope - Page 1
Forum section: electronics / beginners

author: Kelvin_1990
author_rank: Newbie
timestamp: December 12, 2022, 01:43:18 pm
content: It has been noticed that many technicians and mechanics of all ages and skill levels show a clear reluctance to use oscilloscopes in diagnostics. Perhaps this is because the oscilloscope is thought to be difficult to use, and the measurements obtained with it are difficult to understand. But is it?Yes, this was true until recently. But everything in this world is changing, and the era of new technologies is coming. Oscilloscopes are now available with a built-in automatic signal analyzer that provides results in a convenient and understandable way.Let's look at simple signals obtained with an oscilloscope.Testing the battery, starter and alternatorThere are several ways to diagnose the vehicle starting and charging system, none of which will give you a way to visualize what's going on in the system the way an oscilloscope can.Consider an example obtained from a car with a known good battery and charging system.Here is the waveform:Even experienced technicians don't want to waste their time understanding this signal. Although this waveform contains a lot of useful information.Here is the result of automatic processing of such a signal:Impressive?Moreover, the software makes a diagnosis and describes the detected faults.Detection of mechanical failuresDiagnosing engine misfires is the problem we spend the most time on.It is sometimes necessary to disassemble engines to find the root cause of some misfires if relative compression and other tests done in the usual way do not give useful results.Now, we have a way to "see" pressure changes inside the cylinders almost as soon as they happen, eliminating the need to disassemble the engines.Here is a graph of the pressure in the engine cylinder:This signal was recorded on a gasoline engine, where a pressure transducer was installed instead of a spark plug.Let's analyze this signal. Here we can easily find the TDC point.Well, that's probably all...And this is how the result of automatic analysis of the pressure transducer signal will look like:I showed only two examples that allow you to evaluate the diagnostic capabilities using an oscilloscope in just a few seconds.You can learn more about these technologies here:AUTOSCOPE TECHNOLOGY

author: coromonadalix
author_rank: Super Contributor
timestamp: December 12, 2022, 05:39:13 pm
content: The only place i think with a scope you would have some problems is the can bus lines, not sure if they are differential pairs or ground and signal plus ....I'm no car guruthks for the explanationsEDIT, what do you use as scopesince it says usb oscilloscope ?

author: Kelvin_1990
author_rank: Newbie
timestamp: December 12, 2022, 07:18:00 pm
content: Device inputs have a common ground. But you can measure CAN bus signals.This device specializes primarily in in-depth engine mechanical testing and diagnosing engine misfires.It's called USB Autoscope IV.Here is the website -https://usbautoscope.eu/

author: Benta
author_rank: Super Contributor
timestamp: December 12, 2022, 07:41:26 pm
content: The modern testers I've seen in garages do everything: error readout, CAN bus reading, voltage/current/resistance measurement, oscilloscope etc.I see no reluctance on the side of mechanics to use these.

author: Adrian_Arg.
author_rank: Frequent Contributor
timestamp: December 12, 2022, 10:09:46 pm
content: Quote from: Benta on December 12, 2022, 07:41:26 pmWhich one would you recommend?

author: MrAl
author_rank: Super Contributor
timestamp: December 13, 2022, 08:33:29 am
content: Quote from: Kelvin_1990 on December 12, 2022, 01:43:18 pmI have found a scope to help in the past with some battery problems but as you point out they could be useful in other areas too of course.You can see if a diode in the alternator is bad by looking at the charging voltage of the battery or the charging current especially. In the ones i have seen the waveform looks like a three phase full wave rectified wave. If one of the diodes is bad (open) it will look different.You can also look at signals coming from the ECU. Just recently i had to troubleshoot a problematic fuel pump relay which is not just a relay but also has a circuit inside with an IC chip and some other stuff. I could look at the square wave coming from the ECU and also check the electrolytic capacitors with a frequency generator and scope. I found one of the caps had very very high ESR which caused the car to stall randomly and not start back up right away.I'd love to have a scope connected all the time and was working on such a unit using a microcontroller a long time ago but got distracted with other things.The idea is to look at the battery voltage WHILE the engine is being cranked. The scope will show a deep dip when the starter is turning.The depth of that dip reveals the state of the battery health. I'd love to have that installed permanently.

author: Kelvin_1990
author_rank: Newbie
timestamp: December 13, 2022, 11:01:55 am
content: Quote from: Benta on December 12, 2022, 07:41:26 pmYes, almost all technicians use scanners, I mean devices that are connected to the vehicle's diagnostic connector, such as the OBD-II.An oscilloscope connected directly to the engine or to the car's electrical wiring is used less often. I think it's because analyzing the received data is a rather difficult and time-consuming task.Quote from: MrAl on December 13, 2022, 08:33:29 amSuch a tool has already been created and is working on an ongoing basis. It's called"ElPower Script".The idea is precisely to measure the depth of the voltage drop at the battery terminals at the moment when the starter is turned on. At the same time is measured the current drawn by the starter from the battery.All this happens at the moment immediately after the closing of the power contacts of the solenoid relay, when the starter armature has not yet had time to start rotating. Having these two values - the value of the voltage drop and peak current - the software calculates the active internal resistance of the battery, and the active internal resistance of the starter.The internal resistance of the battery shows what kind of real CCA this particular battery has. By the internal resistance of the starter, you can see with which CCA battery is suitable for this car.

author: HighVoltage
author_rank: Super Contributor
timestamp: December 13, 2022, 11:11:19 am
content: Good repair shops always had a scope.Even in the 1960s the scopes were already around in the USA in car repair places.

author: Kelvin_1990
author_rank: Newbie
timestamp: December 13, 2022, 06:50:37 pm
content: Quote from: HighVoltage on December 13, 2022, 11:11:19 amI am also sure that a good workshop must be equipped with an oscilloscope.

author: bdunham7
author_rank: Super Contributor
timestamp: December 13, 2022, 07:41:57 pm
content: Quote from: HighVoltage on December 13, 2022, 11:11:19 amYep, the Sun and Allen engine analyzers were commonly seen in well-equipped shops. I used a digital version, the Snap-On Counselor, in the 80s. So automotive-specific DSO's are pushing 40 years now. I still have my handheld Fluke 98 from ~30 years ago that does a lot of what the OPs device does, including relative compression, ignition analysis, battery and charging test, etc. So this is hardly a revolutionary new concept. That said, the OPs product appears to be pretty good alternative to the automotive Picoscope.

author: Kelvin_1990
author_rank: Newbie
timestamp: December 15, 2022, 08:45:21 am
content: I agree with you that the testing the battery, starter and alternator is available in many devices.But another tests are something new.This is a completely different approach to analysis of the signals.Here is a video of the Px script:Here is a video of the "Phase" tab of CSS script.

author: Bicurico
author_rank: Super Contributor
timestamp: December 15, 2022, 09:15:16 am
content: There are two kind of repair shops, at least in Portugal:1) Official brand dealers, who are obliged to have a repair shop: these will do repairs on the brands they sell, following the official proceedures of the brand. Diagnostics consist mainly of reading out the data stored in the ECU, as well as, other specific tests defined by the brand. Repair consists in exchanging whole modules.2) Unofficial/generic car shops: these repair any brand. In the EU, car brands need to provide access to spare parts and to the ECU for third parties. These shops normally have a professional grade OBD2/whatever reader (i.e. from Bosch, who develops the electronics for the main EU car brands anyway). These read out all error messages and allow to make realtime measurements. I would guess this is enough for most repairs. And if this does not help in finding the fault, the tradional trial&error starts, where suspect components are exchanged from a good car or simply replaced (adding to the bill, as sometimes good parts are replaced, too).Nowadays I don't think there is space for advanced diagnostics on electronics level, where an oscilloscope would be differential in providing a good customer service. You would need an experient electrician and it would simply take too much time! If an ECU board (or whatever) can be bought as reconditioned for a few hundreds Euro, how much would it cost in labor (=time) to find the fault and repair the ECU (or whatever component) in the shop?Conclusion: I don't see it as repair shops being unabled/unwilling to use oscilloscopes! I think they just don't need it: the car testing equipment is powerfull enough and for everything else there is no time or market.

author: G-son
author_rank: Regular Contributor
timestamp: December 15, 2022, 01:13:37 pm
content: Oscilloscopes can be EXTREMELY useful in automotive diagnosis. But not all people are going to get a grip on it, not all are going to like the process, and there's always going to be the code reader based "repairs" where people read the codes, swap the parts they think may cause that code, and hope that fixes the problem. The car usually ends up in the hands of someone who actually can diagnose problems after the parts cannon guys have failed.https://youtu.be/rzxtVAuwiG8

author: Kelvin_1990
author_rank: Newbie
timestamp: December 16, 2022, 11:21:31 am
content: Let's consider three approaches in the diagnosis and repair of cars:The first is the standard approach of car repair and automotive maintenance managers.It all comes down to the implementation of the regulations for maintenance requirements in accordance with the manufacturer's recommendations.The second approach is the attitude of vehicle technician to the maintenance and repair.The standard procedure could not detect the fault (eg code P0300...)In the process of troubleshooting, its possible that some problems were added to the car, for example:when replacing the spark plugs, sand and dirt were not blown out of the chamber;removal of high-voltage wires was carried out without a special tool, which can lead to an internal breakage of the conductive conductor;replacement of the timing belt was not carried out according to the instruction;installation and use of non-genuine spare partsA dozen more examples could be given.But, in the end, the car has not been properly repaired.The third approach is the owner of the car.In any case, he will lose a lot of money and perhaps his car will not be repaired.Conclusion - this is why the Px and CSS scripts are needed before service of your car and after being serviced.They allow you to assess the condition of the engine within a few minutes.