Automotive Technology Course | OBD-2 Repair Strategies 1

Automotive Technology Course | OBD-2 Repair Strategies 1


Oh the obd2 diagnostic system is really composed of nine modes of operation these allow for all the normal scan tool features to take place obd2 is based on the FTP or federal test procedure the FTP is a detailed drive cycle through the streets of a major city like LA all most are accessed behind the scenes invisible to the user mode one is PID or parameter X s also known as reading data stream mode two is freeze frames which is a snapshot of the actual conditions of when the code setting fault actually happened mode three involves retrieving diagnostic codes it is important to mention that not all be one more enhanced codes will show up in generic obd2 modes were involved clearing faulty codes this mode on some vehicles may clear the adaptive or cam memory but not always mode 5 is o2 sensor specific and stores specific information regarding the o2 oxygen sensor minimum and maximum values most successful you and will become even more important in future obd2 Diagnostics it is an engineering mode which will cover further later on most 7 shows vending codes pending coats are one trip codes which only set during the first instance of it happening mode it covers bi-directional controls or being able to trigger the evap vent belt to a closed position this mode may be expanded in the future mode 9 involves the output of ECM specific information such as Ben and Flash software numbers which is useful during reflashing you the mobi d2 connector is the main testing hub for any obd2 vehicle through this connector tests can be done on the alternator starter power and ground feed and complete testing of the vehicle network among other tests pens 4 5 and 16 are chassis and sends her ground and on switched power respectively you the mobi d2 connector used as a diagnostic tool should be the first place to look at during a no start condition using pin 4 you can immediately tell whether the vehicle is grounded properly test the battery and resistance points at the fuse box pin 5 tells you in the ECM is grounded correctly test the main connectors know if all sensors are working and pin 16 allows you to test the ignition switch main relay battery alternator starter and all power feed components if you have no communications with the ECM look at pin 16 which may be tied to the cigarette lighter look for a blown fuse at the cigarette lighter and internal lights which may not be allowing power for communications some scanners will not communicate if this fuse is gone and far is connected straight to the vehicle chassis pin 5 goes right through the ECM itself and is tied to most vehicle sensors and pin 16 although is nuts which is usually connected to the ignition switch steady power fuse box and battery you the obd2 system uses a specific language called a protocol to communicate with the scan tool obd2 has nine different protocols for communication protocols are produced by institutions the SAE or Society of Automotive Engineers and ISO or international standards organization based in Europe as of year model 2008 all vehicles sold in the US have to speak the Kent protocol Kant stands for controller area network and it is a much faster protocol some protocol use two lines or wires for communications this means that each wire is a mirror image of the other but with a different polarity in this case J 1850 protocol uses Pence’s two and ten for communications with a dual wire signalling system the Ken protocol is now the most important protocol for obd2 and it’s mandatory for new vehicles there are four variants of the Kent protocol each a bit faster than the other remember on these networks the ground wire is not the same as chassis ground this is called floating ground a gateways network node or module that matches two different speed networks together the body or instrument cluster module is normally used as the gateway some European vehicles have a separate gateway module the protocol is simply an agreement for communications interchange it also determines what type of voltage signaling waveform timing and IDs for the different modules are used the most common camp protocol as 500 megabits per second also keep in mind that just because the system as fast does not mean that the scanner is fast most current scan tools will slow down communications in order to use their existing hardware using a regular multimeter it is possible to measure an AC signal to chassis ground even though the network may have a floating ground an oscilloscope is the way to go when it comes to network measurements a basic understanding of communication protocols is usually enough for most automotive diagnostic work here we can see going to enter into a real-life Diagnostics process of a vehicle network system using the ad scope one the oscilloscope is the tool of choice when viewing and diagnosing network problems after establishing communications we are now ready to capture and view a real network in action in network communications a ground pulse is called a low and a five to seven volt pulse is called a high don’t worry too much about how high the pulse goes almost all network faults have an at ground level where the signal can’t reach a proper floating or chassis ground a series if flow pulses is decoded as many zeros and a series of hypotheses is decode it has multiple ones in a binary system a combination of lows and highs makes the actual data exchange when measuring network signals set the scope at a slow time setting to be able to capture more cycles on screen here using a faster time rate we can only see the individual cycles therefore here we cannot see the bigger picture individual cycles are okay of trying to determine the health of an actual cycle but doesn’t have much diagnostic value when measuring network communications you are more concerned with how low the signal gets and the signal must reach a minimum of five volts due to the fact that the high communication state is generated by multiple resistors across multiple modules the side of the network rarely fails if you want to see a ground reaching signal all the time be aware that on a floating ground system you have to connect it to both network wires single wire networks use chassis ground here we can’t see on screen the actual single pulses making up the communication notice how the signal has a good ground-level value and the clean high state don’t concern yourself with each individual pulse or the binary sequence of ones and zeros in order to analyze the actual ones and zeros you need an network analyzer which is at this time beyond the reach of most technicians the network analyzer may cost a few thousand dollars and is not necessary for automotive work at this time however given the current state of technology network analyzer allow you to know which module or node is faulty in many cases the faulty node starts outputting excessive cycles talking too much and can bring the whole network down future automotive systems will have all sensors and actuators completely networked with these future systems the map TPS coils injectors in fact every component will be eight so node or module already the throttle actuator accelerator position sensor and steering wheel position sensors are completely networked in some systems a fully networked vehicle is the way of the future as we can see here on screen the actual single pulses are not important just the fact that the communication signal is reaching proper ground a shorted network which is very common will always show up as a grounded waveform by the same token if the network hallways shows up as hike then the termination resistors are missing which points to a faulty module some protocol use two lines or wires for communications this means that each wire is a mirror image up the other but with a different polarity in this case J 1850 protocol uses pens two and tenth for communications with a dual wire signaling system the most common camp protocol as 500 megabytes per second also keep in mind that just because the system as fast does not mean that the scanner is fast most current scan tools will slow down communications in order to use their existing hardware using a regular multimeter it is possible to measure an AC signal to chassis ground even though the network may have a floating ground an oscilloscope is the way to go when it comes to network measurements so again a shorted module shows up has a low signal and a high signal at all times means that the termination resistors are damaged where the termination resistors are located and which module provides the bias voltage for the network is not published information this is one of the hardest things to determine during Network Diagnostics each vehicle make and model is different and a waveform library with given data points module circuitry and proper documentation will have to be made on your end a process of disconnecting each module at time often works fine during Diagnostics the rule of thumb is as follows most instrument clusters serve as termination resistors and most ECMs and body modules serve as voltage regulators sometimes the body modules also may serve as termination resistors in obd2 Diagnostics running the drive cycle equates as proving to repair without using mo6 it is always necessary to run the drive cycle to prove your repair and if you hunger in an emission repair state you also need to run the drive cycles for the vehicle to pass inspections a drive cycle tells the specific way to run the vehicle so as to run all monitors keep in mind that monitor is a test for a specific system setting a monitor to complete may or may not issue a faulty code a completed monitor has nothing to do with the faulty code the drive cycle is based on the FTP or federal test procedure which is a conditional drivability scheme when driving though the streets of a big city the Diagnostics executive is the central program that runs all diagnostics the de tells the task manager what to do which in turns runs the monitors sets codes freeze frames and all obd2 dedicated diagnostics here’s a chart which denotes the difference in time savings between running the drive cycle as opposed to using most six continuous monitors will run almost instantaneously we have said throughout this video that tracing codes should always be the last step except when using the continuous monitors during open shorts sensor and misfire Diagnostics it is sometimes necessary to erase codes for a retest non continuous monitors will run according to the drive cycle there are more than 13 of these monitors and they are not always present all at the same time the GR secondary air convertor o to sensor o to heater a PAP thermostat and PCV monitors are typically found in today’s systems the obd2 monitoring system is always changing as technology demands it the mobi d2 diagnostics path is to repair the vehicle gather drive cycle procedure then run the monitors to finish it is important to know if a specific monitor is supported especially if running the vehicle through inspection on screen we can also see the separate continuous and non continuous monitors I see honest pc-based can tool the use of a code information system integrated with the scanner is a must in this case we have access to code setting criteria right on the scanner as well as the ability to integrate the entire diagnostic code environment current pending Cosette in criteria normal values and code erasure the more information that you have at your fingertips the better off you’ll be the mobi d2 Diagnostics path is to repair the vehicle gather drive cycle procedure then run the monitors to finish then once completed recheck four coats and lies the CSC or code set in criteria and start over if no codes are present than you’re home free you you the structure of an obd to code has a p c b or u for the first digit with its dedicated solution ons the second digit has now been expanded to 0 1 2 & 3 digits 2 & 3 are now generic as well remember clearing codes is always the last step with few exceptions so gather data repair and clear codes important there are two types of codes drivability and open short type of code some scan tool definitions will let you know which type you have if presented with an electrical open or short high or low value pull out the multimeter or scope not all scanners will advise you of the type of code if inbound look up the code definition in another book or source the type of code will determine your diagnostic path misfire coats are extremely common in today’s diagnostic arena in this case we have a code P 0 3 0 4 or misfire on cylinder 4 a major source of misfire is also the mass airflow sensor this typical drive cycle is shown with details on a dual curve chart notice the different tax seller ation and deceleration procedures using the freeze frames to diagnose this code we arrive to the following conclusion the engine was cold vehicle not moving no low present and engine running lean what could have caused this misfire this misfire was not caused by a rich condition since the engine was leaned rich air fuel mixture is seldom the cause of a miss and ignition misfires normally happen at high loads and there was on the fuel trims at 25 and 14 percent respectively point to lean condition and the mass airflow not treating properly the intake gasket was found faulty the giveaway are the fuel trims very high leading to lean misfire fault in our PC scanner we see how oftentimes the freeze frames are very limited in data output don’t be discouraged even a minor parameter is all you need to connect the dots newer opt to systems are richer in data output when it comes to freeze frames by using the freeze frames properly you can get an insight into why and how the particular code was set if faced with a continuous monitor code such as an open or short misfire code it may be necessary to go back and forth between clearing and accessing codes grabbing your freeze frames analyzing your code setting criteria performing the repair and starting all over again in a way electrical faults are more time-consuming but easier to repair due to its straightforward process as a final note also get into the habit of retrieving the entire data stream only once and comparing it to the freeze frames this comparison scheme allows for the normalization of data across the board it is also possible that an old freeze frame is still stored in memory the obd2 diagnostics path is to repair the vehicle gather drive cycle procedure then run the monitors to finish then once completed recheck for codes analyze the CSC or code set in criteria and start over during an electrical repair only clearing retrieving and vandalizing data is the best option there obd2 systems are richer in data output when it comes to freeze frames you


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