LAN operates on serial data at 3 speeds low speed 33.33 kbps to 83.33 kbps single wire response time 100 to 200 ms used for operator-control functions mid speed 92.5 kbps used for informational or entertainment applications large quanties of data in short period of time high speed 500 kbps 2 wire used for powertrain and chassis devices and to share "real time" data soon probably the only approved diangnostic datalink technology NODE operates in one of 3 states startup ECU intilizes communication and is capable of communcation fo r 8 seconds Communication startup ECU monitors bus for network management messages indicating requests for other ECUs on the network Node shutdown only occurs when there are no control operations requiring ECU Network Management, each ECU operates independent of others, each collection of ECUs is a virtual network, desigened to reduce overall power consumption Can Data is seperated into frames 8 bits long single frame under 8 bits, multi frame over 8 bits all in the network transportation layer USDT is for all diagnostic requests UUDT always single frame and positive response messages only. System diagnostics warm up cycle coolant temp rises 44 degree to minimum of 160 MIL is on for only A and B (emision) codes, flashes for catalist damage, turns off after 3 consecutive pass under the same conditions that set the DTC Service lamp iluminates for type C DTCs (non-emisions) OBD IIDiagnostic Trouble CodesPage 1 of 23OBD-obd170010 Specific vehicle powertrain system codes: 0=Fuel and air metering and auxiliary control 1=Fuel and air metering 2=Fuel and air metering (injector circuit) 3=Ignition system or misfire 4=Auxiliary emission controls 5=Vehicle speed control or idle control 6=Computer output circuit 7=Transmission 8=Transmission 9=Transmission The last two digits indicate the component or section of the system that has the fault. (Note: Generic DTCs can be read by generic scan tools.) Type A and Type B DTCs illuminate the MIL. Type A DTC: Is emission related Requests illumination of the MIL on first failed trip Stores history DTC on first failed trip Stores freeze frame on on first failed trip (if empty) Stores fail record Updates fail record the each time test passes, fails, or does not run Type B DTC: Emissions related "Armed" after one trip with fail "Disarmed" after one trip with pass Requests illumination of MIL on second consecutive trip with fail Stores history DTC on second consecutive trip with fail (DTC is armed after first fail) Stores freeze frame on second consecutive trip with fail (if empty) Stores fail record when first test fails Type C (or C1) DTC: Non-emissions related Requests illumination of service lamp or service message on DIC on first failed trip Stores fail record when test fails Updates fail record first time test fails each ignition cycle Stores history DTC on first trip with fail Does NOT store freeze frame Type D (or C0) DTC: Non-emissions related Does NOT request illumination of any lamps Does NOT store freeze frame Stores history DTC on first failed trip Stores fail record when test fails Updates fail record first time test fails each ignition cycle Type X DTC: Coded into PCM software, but used mostly for vehicles that do not require MIL illumination Will not illuminate MIL or store DTC, freeze frame or fail record Used on some domestic vehicles Can still be used for supplemental diagnostics even though codes are not stored CAPTURE INFO function: Stores DTCs, Freeze Frame and Fail Records Allows you to clear DTCs from vehicle and have information available for reference Has STORE INFO function, allowing you to store data from PCM into Tech 2 Has REFRESH INFO function, allowing you to replace data stored in scan tool with new information from PCM CAPTURE INFO data saved in scan tool memory is not cleared by CLEAR DTC INFO command Is different from SNAPSHOT in that it is typically only one frame of data System status information: Displays Inspection/Maintenance (I/M) flags (also known as Readiness/Function Codes) Identifies if vehicle's emission controls have been diagnosed Required in some states for inspection and maintenance test programs Used to verify repairs Displays emission related tests and their status (YES or NO in regards to completion) HO2S Heater/Evap System, idel 2 min in park for AT in nutural for manual transmissions, all accessories turned off cold start ECT and IAT and within 5 C of each other at startup. EVAP, Air Oxygen Sensor, and Catalyst Test, Acceleralt to 55 mph part throttle until engine reaches operating temp (8-10 min) steady state cruise at 55 mph for 6 min. EGR Test, decelerate to 45 mph and maintain apeed for 1 min perform 4 decelerations of 25 seconds each with no braking return to 45 mph for 15 seconds between each deceleration. Catalist, Oxygen Sensor, Evap Tests, at speed of no less than 25 mph accelerate to 55 mph cruise for 2 min decelerate to 0 mph let engine idle for 2 min with service brake depressed and automatic transmission in drive or manual transmission in nutral with clutch depressed Cold start requirements: Barometric pressure greater than 75 kPA Engine coolant temperature (ECT) below 30°C or 86°F Intake Air Temperature (IAT) below 30°C or 86°F IAT and ECT temperature difference of less than 5°C or 7°F Battery voltage between 10.5 and 16 volts Fuel level between ½ and ¾ Coolant temp sensor 5v ECT cold is high resistance, resistance decreases and PCM measure lower resistance at 122 F the PCM decreasese is internal resisance to achieve a greater resistance so the siganl voltage increases althought the resistance continues to decrease. Heated Oxygen Sensors Monitor voltage and response rate of pre-catalyst sensors Monitor output voltage of post-catalytic sensors Monitor heating system for performance Consists of 3 diagnostic tests for HO2S: Time to Activity Response Time Sensor Voltage The diagnostics are disabled if one of the following criteria are met: Faults related to TPS, MAP, ECT, MAF, IAT sensors, fuel injectors, AIR, EGR, and EVAP diagnostics are present Intrusive diagnostic test is active Battery voltage is outside calibrated voltage range Traction control engaged Intrusive response diagnostic: Improves response diagnostic Allows diagnostic to take control of oxygen sensor switchpoint and increase frequency of fuel control closed loop operation Can be enabled or disabled - if disabled, diagnostic runs in passive mode Two fuel trim sensors: Six circuits: Calibration circuit Switched battery positive to heating element ECM-switched ground to control the heating element Reference ground Two signal leads Oxygen cell - fixed voltage on its signal circuit Amperometric cell - current increases or decreases in direct proportion to engine exhaust gas oxygen content Wide-range lambda sensors: Continously identify oxygen content of exhaust gas Allow ECM to reach optimum air to fuel ratio more efficiently than toggle sensors When diagnosed with a Tech 2: 1 lambda = optimum air/fuel ratio The three-way-catalytic converter: Converts HC and CO to H2O and CO2 through oxidation Reduces NOx to nitrogen and oxygen Over 1 lambda = lean condition Under 1 lambda = rich condition The post-converter HO2S should have a fairly inactive voltage output signal if the catalyst is good. Catalytic converter storage capacity: Requires engine and catalyst stay at steady cruising speed to record oxygen samples PCM runs 2-stage diagnostic in 1998 vehicles: Stage 1: PCM calculates oxygen capacity of catalyst and compares it to calibrated fail value If Stage 1 fails, test enters Stage 2 to continue monitoring catalyst storage capacity to increase test accuracy If Stage 2 fails, test reported as failed, DTC sets Three-way catalytic converter monitor test: Can use counter on scan tool to monitor progress of diagnostic in pre-1998 vehicles Can use idle catalyst monitor function in scan tool in 1998 and later vehicles Increments from 0 to 49 samples and rolls over to 0 at least twice to complete catalyst monitoring Requires 3 or more 50 sample tests to report failure Has staged testing levels to allow PCM to statistically filter test info to prevent false pass or fail and to detect marginal or old catalysts Is more analytical than comparing oxygen sensor activity on scan tool Bases calculations on internal statistical filters Idle catalyst monitor (ICM): Tests oxygen storage capacity (OSC) of catalytic converter at idle instead of road speeds Exercises diagnostic until catalyst diagnostics I/M flag is set for vehicles that have not set this flag Causes of catalytic converter failure: Poor engine performance Excessive fuel consumption Excessive oil consumption Contamination Source of false converter DTCs: Exhaust leaks Aftermarket parts Types of misfire monitoring required: Catalyst-damaging: Detects misfire within 200-1000 crankshaft revolutions Sets Type A DTC and flashes MIL Illuminates MIL steadily when no longer catalyst-damaging Emissions-threatening: Detects misfire within 1000-4000 crankshaft revolutions First trip arms DTC (Type B) Diesel engine misfire monitoring: Started appearing on diesel engines in 1999 Performed when engine reaches calibrated temperature and has operated at steady idle for about 90 seconds Has control module monitor crankshaft position sensor for variations when operating conditions are met If crankshaft speed for any one cylinder is less than expected, control module increases amount of fuel for that cylinder If amount of fuel reaches calibrated value, control module interprets this as misfire and sets DTC Used only to identify weak cylinder requiring additional fuel Second trip fail sets DTC and lights MIL Can set DTC on non-consecutive trips if under similar load as previous misfire Misfire relief: Allows more crankshaft revolutions with misfire before turning on MIL Prevents owner dissatisfaction by not turning on MIL for insignificant misfires Full range misfire detection: Began rolling out in 1997 Full range misfire detection at all positive speed/load conditions up to redline Prior to full range misfire detection, misfire was only monitored in FTP test region If a rough road is detected, the diagnostic can be disabled Two methods of detecting rough roads: Software (crankshaft sensor signal) ABS wheel speed sensors Software approach: Processed crankshaft sensor signal used by misfire diagnostic Detects patterns characteristic of rough roads Antilock brake system (ABS) wheel speed sensors: Can sense rapid variation of wheel speed due to rough roads Sends signal to PCM indicating rough roads Used on wide range of vehicles equipped with ABS as standard equipment IAC controls idle air, coarse adjustment Timing, fine adjustment for idle speed Idle control monitoring diagnostic includes passive and intrusive testing. Pre-1998 vehicles idle control monitoring: Passive testing Intrusive testing Fuel trim is controlled by either open or closed loop: Open loop: When PCM determines fuel delivery based on sensor inputs (except oxygen sensors), internal programming, or LTFT values Closed loop: When PCM determines fuel delivery based on input of many sensors, including oxygen sensors, internal programming, and LTFT values PCM uses input from oxygen sensors to calculate long-term and short-term fuel trims If oxygen sensors indicate lean condition, fuel trim values will be above 0% If the oxygen sensors indicate rich condition, fuel trim values will be below 0% Fuel trim values that are between +10% and -10% are an indication that the PCM is maintaining proper fuel control. PCM monitors fuel trim: Continuously DTC will set if fuel trim causes emissions to exceed FTP by 1.5 times Proper control of fuel trim achieved when fuel trim numbers are +10% or -10% Fuel Trim Cells: Used to determine need to set fuel trim DTC Uses cells to represent operating conditions Has weighted cells used to set fuel trim DTC: - As weight of cell increases, chances increase of DTC setting - Based on FTP testing and OBD II Monitors averages of long-term and short-term fuel trim Indicates malfunction if fuel trim values reach and stay at their limits for period of time Compares long-term and short-term trim values to rich and lean limits: - Records PASS if either value is within fail thresholds - Stores DTC and rich or lean condition if both values are outside fail limits Conducts intrusive test to see if rich condition is caused by vapor from EVAP canister Will not set DTC unless count in weighted cells Will not set DTC if vehicle has problem under conditions located in unweighted Exhaust gas recirculation reduces NOx emissions by reducing combustion temperatures. EGR affects manifold pressure: EGR on - increases manifold pressure EGR off - decreases manifold pressure EGR system is considered malfunctioning when: EGR components fail Change in EGR results in vehicle emissions exceeding 1.5 times FTP emissions standards EGR Diagnostic tests include: Linear EGR pintle diagnostic Linear EGR flow rate diagnostic EGR flow rate diagnostic test, closed during stead state cruise or open under closed throttle deceleration, determined by the diagnostic calibration, average of MAP values are taken for pass fail EGR flow rate diagnostic: Is usually run once per ignition cycle Is run multiple times if fast initial response feature or rapid step response feature is enabled Is intrusive in that it opens EGR valve when it is normally closed or vice versa Can result in change in engine speed on vehicles with automatic transmissions during deceleration test Does not affect vehicle operation, though customer may notice fluctuation on vehicles with tachometers EGR flow rate diagnostic for diesel engines: Uses MAF sensor information to monitor EGR flow rates Performed during steady cruise state Indicates no EGR flow when larger than expected quantity of air is measured by MAF during test Secondary air injection reaction (AIR) system: Uses pump to create air flow into exhaust stream Promotes oxidation of HC and CO by adding oxygen to exhaust until closed loop entered Gives low voltage (0-2mili v) reading when HO2S becomes active if secondary AIR pump is delivering air to exhaust Secondary air injection reaction (AIR) system (continued): Monitoring of airflow presence in exhaust stream and functional monitoring of secondary AIR pump or switching valves is required by OBD II Monitoring of amount of airflow is not needed if airflow distribution system is durable or leak proof for life of vehicle or if emissions impact of total secondary AIR system failure is less than 1½ times FTP standards uses passive and active test: passive test looks for voltage at pre-cat voltage prior to closed loop and toggle upon the pump being turned off. active test actives the air pump during normal operating conditions looks at pre-cat O2 lean reading indicates corrrect operation. This will put the vehicle into open loop but should not be perceptible. It will only be run if the passive test fails or is inconclusive. 2 consecutive fails to iluminate MIL OBD illuminates for leaks in EVAP system with diameter equal to or greater than: 0.040" for some MY 1996-1998, and all MY 1999 or later vehicle 0.020" for some MY 2000 and later vehicles Applications with larger gas tanks may have special permission to do larger leak tests On carts and light duty trucks meeting new standard Identify leaks Verify repairs Engine-off natural vacuum diagnostic (EONV): Utilizes temperature changes in fuel tank following drive cycle to generate vacuum Relies on pressure change to determine whether system is leaking PCM can detect small leaks as small as .020 inch IMPORTANT - Read all of the instructions before exiting this course. • Save your student diskette! • To obtain credit for this course, electronically send (upload) the information on your student diskette after exiting this course • Click Start, Programs, and GM STC • Select GM STC Final Test Upload • Follow the directions displayed in the GM STC Final Test Upload program • For future reference, the student diskette for a completed course allows you to navigate freely through the course • The upload computer must have an internet connection AND the GM STC Final Test Upload program • To exit this course: • Click the Exit tab at the top of this screen OR • Click the Next button on the side of the screen