Oscilloscope and Scan Tool Use for Vehicle Electronic Systems

APTE7504 – Vehicle Electronic DiagnosisWeek 3

Praneel Chand

Introduction• Diagnostic techniques are linked to the use of test equipment• Learning how to use tools is a practical skill• However, you can follow some guidelines to use tools correctly and

for their intended purpose• This lecture will discuss the two main types of tools used for vehicle

electronic system diagnosis• Oscilloscopes• Scan Tools

Oscilloscopes[1] - Introduction• Traditionally two types: analogue or digital• Digital scope is now universal• An oscilloscope draws a graph of voltage

(vertical scale or Y axis) against time (horizontal scale or X axis)• The trace moves across the screen (left to

right) and the ‘flies back’ to start again• The frequency at which the trace moves

across the screen is known as the time base – can be adjusted automatically or manually

Automotive Oscilloscope Kit (Source: www.picoauto.com)

Oscilloscope Graph (Source: www.picotech.com)

Trace = waveform = pattern

Oscilloscopes[1] - Introduction• The signal being tested can be amplified or attenuated (reduced) like

changing the scale on a voltmeter• The trigger, which starts the trace moving across the screen can be

caused internally or externally.• The voltage signal under test is A/D converted and the time base is a

simple timer or counter circuit.• Because the signal is plotted digitally on a screen from data in

memory, the picture can be saved, frozen or printed• The Pico Automotive Diagnostics kit turns a computer into a powerful

automotive diagnostic tool for electronic diagnosis

Oscilloscopes[1] - Introduction• The scope can be used to measure and test virtually all of the

electrical and electronic components and circuits in any modern vehicle• Excellent software is included – the user can simply select the sensor

or circuit to be tested and the software will automatically load the required settings• However, in diagnostics it is also important to be able to manually

adjust the oscilloscope settings in case the readings are out of range• So we will look at how to adjust the time base, voltage amplification,

and trigger manually.

Oscilloscopes- Time Base [2]• Most scopes use 10 divisions from left to right on the display• Setting the time base means setting how much time will be displayed in

each division• The time base should be set to allow two to four events to be displayed• Milliseconds is commonly used in scopes when adjusting time base• Hence, sample time is milliseconds per division (ms/div)• Increasing the time base reduces the number of samples per second• Total time displayed on screen is the product of number of divisions

(usually 10) and the sample time (ms/div)

Oscilloscopes- Time Base [2]• Time per division settings can vary greatly in automotive use e.g.• Network (CAN) communications network: 2 ms/div (20 ms total)• Throttle position (TP) sensor: 100 ms/div (1 sec total)• Voltage measurements: 5 ms/div (50 ms total)

• The total time displayed on the screen allows comparisons to see if the waveform is consistent or is changing

Oscilloscopes- Volts per Division [2]• Volts per division (V/div) should be set to that the entire anticipated

waveform can be viewed e.g.• Throttle position (TP) sensor: 1 V/div (10 V total)• Battery, starting and charging: 2V/div (20 V total)

• Notice that total voltage to be displayed exceeds the components voltage range. This allows for unexpected voltage readings

Oscilloscopes- DC and AC Coupling [2]• DC coupling is the most used position on a scope because it allows the

scope to display both AC voltage and DC voltage signals present in the circuit• AC part of the signal rides on top of the DC component• In AC coupling mode a capacitor is placed into the meter lead circuit to block

all DC voltage signals but allows the AC portions to pass and be displayed• AC coupling can be used to show output signal waveforms from sensors

such as:• Magnetic wheel speed sensors• The AC ripple from an alternator• Magnetic crankshaft position sensors

Oscilloscopes- DC and AC Coupling [2]• Check the instructions from the scope manufacturer for the

recommended settings to use. Sometimes its necessary to switch between AC and DC coupling to properly see some waveforms.

Oscilloscopes- Triggers[2]• External Trigger• The waveform starts when a signal is received from another external source

rather than from the signal pickup lead• E.g. external trigger comes from the probe clamp around the cylinder #1

spark plug wire to trigger the start on an ignition pattern

• Trigger Level• Is the voltage that must be detected by the scope before the pattern will be

displayed• A scope will only start displaying a voltage signal when it is triggered or is told

to start.

Oscilloscopes- Triggers[2]• Trigger Slope• Is the voltage direction that a waveform must have in

order to start the display.• Most often, the trigger to start a waveform display is

taken from the signal itself.• In a positive trigger, the trigger occurs at a rising (positive)

edge of the waveform.• In a negative trigger, the trigger occurs at a falling

(negative) edge of the waveform.• Sometimes you need to change between negative and

positive trigger if a waveform is not shown correctly.

Positive Trigger

Negative Trigger

Oscilloscopes- Videos & Web Resources from Pico Automotive (available on Moodle)

• PicScope basics video• Part 1 looks at time base and voltage division adjustment,

using multiple channels, current measurement with inductive probe, trigger use• Part 2 looks at buffers (time base, sampling, and

waveform)

Oscilloscopes- Videos & Web Resources from Pico Automotive (available on Moodle)

• PicScope Scope School Readings• Part 1 - Introduction to PicoScope

• Taking a measurement - covers the following key elements: Probe, Voltage, Time, and Trigger

• Part 2 - The next step• Looks at Rulers, Zooming, Custom settings, Saving & sharing

• Part 3 - Tips and tricks• Looks at Coupling, Buffers, Reference waveforms, and individual channel scaling

• PicoScope 6 Automotive: Introductory training notes• Gives a basic overview and introduction to PicoScope 6 Automotive, including both the

software itself and the hardware (PicoScope unit)

Oscilloscopes- Videos & Web Resources from Pico Automotive (available on Moodle)

• PicScope Automotive Guided Tests• Over 150 guided tests and includes example waveforms and scope settings• Charging & starting• Sensors• Actuators• Communication networks – CAN, LIN, FlexRay

Scan Tools – Introduction (On-board Diagnostics OBD) [1]

• Scan tools are used for on-board diagnostics (OBD)• OBD systems give the vehicle owner or technician access to information for

various vehicle systems• Diagnostic information from OBD has grown considerably over the years

since its introduction in the early 80s• Early versions of OBD would simply illuminate a malfunction indicator light

(MIL) if there was a problem but did not provide any info about the problem• Modern OBD systems (OBD-II) uses a standardised digital communications

port to provide real-time data in addition to standardised diagnostic trouble codes (DTCs)

Scan Tools –Serial Communication Port [1]

• ECUs contain self-diagnosis circuits in modern cars• The diagnostic information produced is read via a serial link using a

scanner• A special interface (OBD-II interface) following a standard protocol (5

types) is required to read the data. This allows many vehicle electronic systems to connect to a central diagnostic plug.• The sequence of event to extract DTCs from the ECU is as follows:1. Test unit (scanner) transmits a code word2. ECU responds by transmitting a baud rate recognition word

Scan Tools –Serial Communication Port [1]

3. Test unit adopts the appropriate setting4. ECU transmits fault codes• The test unit (scanner) converts the DTCs to suitable output text• Further functions are possible and may include:• Identification of ECU and system to ensure appropriate test data• Read out of current live values from sensors. Improper values can be recognised• System function stimulation – testing actuators and watching for response• Programming system changes – e.g. changes in basic timing

Scan Tools –OBD-II Signal Protocols [1]• 5 different signalling protocols are permitted with OBD-II• Most cars implement only one of them• It is often possible to deduce the protocol based on which

pins are present on the connector (J1962)• SAE J1850 PWM (Ford)• Pin 2: Bus +• Pin 10: Bus –• High voltage is +5V• 12 byte message length

OBD-II Port 16 pin connector (J1962) [1]4 – battery ground/earth7 – K-line15 – L-linr16 – battery positive

Scan Tools –OBD-II Signal Protocols [1]• SAE J1850 VPW (General Motors)

• Pin 2: Bus+• Bus idles low• High voltage +7V• Decision point is +3.5V• 12 byte message length

• ISO 9141-2: (Chrysler, European, Asian vehicles)• Pin 7: K-line• Pin 15: L-line (optional)• UART signalling• K-line idles high• 12 byte message length

Scan Tools –OBD-II Signal Protocols [1]• ISO 14230 KWP2000 (Keyword Protocol 2000)

• Pin 7: K-line• Pin 15: L-line (optional)• Physical layer identical to ISO 9141-2• 255 bytes message data field

• ISO 15765 CAN (made by Bosch for automotive & industrial control)• Since 2008 all vehicles sold in US (and most other places) are required to implement CAN as

one of their signalling protocols• Pin 6: CAN high• Pin 14: CAN low

• All OBD-II pin-outs use the same connector but different pins • Exceptions are pin 4 (battery ground) and pin 16 (battery positive)

Scan Tools –OBD-II Signal Protocols [3]• ISO 15765 CAN (made by Bosch for automotive

& industrial control)• Since 2008 all vehicles sold in US (and most other places) are

required to implement CAN as one of their signalling protocols

• Since most modern cars have ECUs with a CAN interface for exchanging data between electronic systems, this option for communication with the tester (scan tool) has become dominant

Diagnosis connector with pin outs for various standards [3]

Scan Tools –Videos (can be accessed via Moodle)• Open the page Scan Tools Videos under “In class” in Week 3 section1. How to use an OBD-II Scan Tool2. Petroject: Hanatech Scan Tool Demo• Demonstration on using the Hanatech Ultrascan P1 which is similar to the

Multiscan P1 (which the department has) but with added features of graphing capability and 4 channel oscilloscope.

Scan Tools –Web Resources (can be accessed via Moodle)• Open the page Scan Tools Web Pages under “In class” in Week 3 section1. Scan Tool Help

• Basic introduction to scan tools and types: Code readers, scan tools, DIY scan tool product information, Professional level scan tools, scanner software (software that transforms your desktop or laptop PC, tablet, smart phone etc into a code reader or scan tool)

2. How to Read Diagnostic Trouble Codes (DTCs)• Contains information on how to read DTCs using a scan tool. An eight step process

outlined for reading fault codes and clearing them. The diagnostic fault codes is an alphanumeric code which you need to find the definition of. You need to search the internet or get the info from the car manufacturer. Fortunately, there are some online databases for getting fault code definitions (see 4. Actron Diagnostic Code Lookup and 5. Bosch Diagnostics below as examples)

Scan Tools –Web Resources (can be accessed via Moodle)• Open the page Scan Tools Web Pages under “In class” in Week 3 section3. OBD-II CAN Diagnostic Codes• Full list of CAN network communication diagnostic codes for the various

communication buses control module communications.)

4. Actron Diagnostic Code Lookup• Online DTC code look up

5. Bosch Diagnostics• Includes resources on DTC code look up and vehicle coverage charts

Student Activity Time

• Use the Picoscope oscilloscope to measure the CAN bus, actuator, and sensor signals on the demonstration model• Use the Hanatech Multiscan P1 to retrieve diagnostic codes from the

workshop car.

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Electronic System Diagnosis and Repair• You will learn how to diagnose various vehicle electronic systems later

on in the semester (weeks 9-13)• You will learn about the scope and of the rectification (repair) process

in the last weeks of the semester

References• [1] T. Denton, Advanced Automotive Fault Diagnosis: automotive

technology: vehicle maintenance and repair. NY: Routledge, 2012.• [2] J. D. Halderman, Diagnosis and Troubleshooting of Automotive

Electrical, Electronic, and Computer Systems. NJ: Pearson, 2012. • [3] R. Bosch, Bosch Automotive Electrics and Automotive Electronics

Systems and Components, Networking and Hybrid Drive. Germany: Robert Bosch, 2013.