Engine compression test: Determines condition of rings, valves and head gasket Normal compression: 1st stroke at least 40% of total specified value Successive strokes build to specified value Application specifies 160 psi: 1st stroke should read around 64 psi Following strokes build evenly to 160 psi Determines condition of rings, valves and head gasket Cylinder with lowest reading not less than 70% of highest Example - Application calls for 160 psi: 70% equals 112 psi If reading was lower than 112 psi, cylinder inspection is necessary Normal compression: Low compression caused by worn valves: Measurement is low on first stroke Does not build up even with addition of oil Low compression caused by leaking head gaskets: Same result as worn valves Engine coolant may be identified in crankcase Could cause low readings on paired cylinders Refer to service information Cylinder leakage test: Isolates cause of low reading or faulty cylinder Perform using J-35667-A Measures air lost from cylinder on compression stroke with both valves closed Initial leakage 12-18% Note any cylinder with more leakage Cylinder with more than 30% leakage requires service: Listen for air leaking from intake, exhaust, crankcase, and cooling systems Air bubbles in cooling system indicate leaking head gasket Manifold vacuum test: Intake stroke of piston creates vacuum Vacuum is any pressure lower than atmospheric pressure Performance suffers when engine loses vacuum Low compression or high leakage will not produce sufficient vacuum to draw in air/fuel mixture Vacuum is greater when throttle plate is closed, lower when open Tests an engine's ability to run efficiently 15-22 exept 60 degree v6 where 12-16 is normal low steady 12-15 leak around piston late ignition or late valve flucuation 1-2 at idle indicates a burned valve or a plug not firing intermitent fluxuation sticking valve intermittent missfire or rich/lean air fule mix normal at idle but fluxuation at higher speeds weak valve springs; valves sticking in guide excessive vibration at idle but returns to normal at higher speeds is worn valve guides excessive vibration at all rpm leaky head gasket needle drifts between 3-6 intake system leak normal at idle but drops to near zero and rises to below normal restrictions in exhaust system Exhaust system: Affects airflow through engine Exhaust pipe diameter: Must allow for proper rate of expulsion with minimal back pressure If gases not expelled effectively, air/fuel charge is diluted, resulting in poor engine performance Catalytic converter: Controls exhaust emissions Deterioration of converter materials can cause excessive backpressure and affect engine performance Excessive backpressure most noticeable at high speeds and heavy loads Customer concern might be "lack of power" Refer to service information for exhaust backpressure testing procedures OBD II: Series of regulations intended to reduce vehicle emissions Powertrain and emission-control systems must be monitored for failure and deterioration Provisions for standardization of diagnostic, repair and service information Federal Test Procedure (FTP): Government-mandated emissions testing program Sets maximum allowable emissions levels MIL must illuminate if system or component fails or deteriorates Federal Test Procedure (FTP): Specific vehicle powertrain system codes: 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 and Idle Control 6=Computer Output Circuit 7 & 8=Transmission The last two digits indicate the component or section of the system having the fault. Five DTC types: A, B, C, D, X Each directly related to diagnostic test Type A DTC: Emissions related Upon first trip with a fail: MIL is illuminated History DTC is stored Freeze Frame is stored Fail Record is stored Fail Record is updated first time test fails during each ignition cycle Type B DTCs: Emissions related Require two consecutive trips with failure before turning on MIL Armed after one trip with a fail Disarmed after one trip with a pass Second consecutive trip Illumination of MIL Stores History DTC Stores Freeze Frame Fail Record is updated first time test fails during each ignition cycle Type C (or C1) DTCs: Non-emissions related First trip with a fail causes: Illumination of service lamp or service message on DIC PCM to store history code and fail record Update fail record first time test fails each ignition cycle Do not store a Freeze Frame Type D (or C0) DTCs: Non-emissions related Do not request illumination of lamps Do not store freeze frame Store history DTC on first fail Store a Fail Record Update Fail Record first time test fails during each ignition cycle Type C1 and C0: May not show up in service manual Used to differentiate changes to Type C & D diagnostics Type C became C1 Type D became C0 Type X DTCs: Disabled diagnostics coded in software For export vehicles No MIL or DTC storing Used on some domestic vehicles For supplemental diagnostics Tech 2 scan tool: Developed in 1996 Required for service of all 1997 and later vehicles Supports 1992 and later vehicles One-handed operation Adjustable screen control Audible error signals Self-test functions Uses 32 MB flash programmable memory card PC interface port Port for future instrumentation Special features of Tech 2 scan tool: 9 parameter screen display 5 parameter freeze option for scrolling Bar graph and line chart capabilities Current data capture Ability to store two snapshots and one capture info Long-term storage of snapshot and capture info data Typical Tech 2 data list: Engine 1 - majority of data viewed here Engine 2 Engine 3 (optional) Transmission 1 & Transmission 2 Data lists split to increase display speed DTC messages displayed under DTC on Tech 2 Last Test: Indicates DTC that passed or failed last test run Last test run could have occurred during earlier trip This Ignition indicates: Passed or failed ignition cycle Whether MIL was requested Since Cleared indicates DTC passed, failed, or been set as history DTC Capture Info function: Stores DTCs, Freeze Frame, and Fail Records Data held in PCM allows you to clear DTCs and still have information available for reference Menu selection Store Info: Stores data from PCM memory into Tech 2 memory Refresh Info replaces data stored with new information from PCM memory Info cleared when refreshed with current data from PCM Tech 2 Snap Shot allows technician to freeze engine operating parameters System Status information: Displays Inspection/Maintenance (I/M) flags Readiness/Function Codes Identifies OBD system diagnosis Required in some states for Inspection/Maintenance test programs Helps determine if diagnostics have run when verifying repairs Displays emission control systems under Test heading Each diagnostic requires at least one test "No" changes to "Yes" when all tests are completed System Status does NOT reference pass/fail status of diagnostic DTC will indicate diagnostic failure Special Functions menu: Allows access to output controls and other special tests Ability to perform system resets such as: Fuel Trim Reset ABS Auto Bleed Set-up instructions for selected test is displayed List of data parameters with available Soft Keys is displayed Special Function tests control: Solenoids Devices normally controlled by vehicle on-board computer When technician commands device ON: Vehicle computer turns device ON, regardless of what inputs would normally be needed Helps determine where fault is occurring EVAP system: Collects fuel vapor from fuel tank Stored in canister filled with activated carbon Allows vapors to be drawn from canister back to engine Enhanced EVAP system: Developed to meet stricter emission standards In 1996, MIL was illuminated when system detected emission leak equal to .040” or greater In 2000, MIL illuminated if OBD II detects leak of .020” or greater Pressure switching solenoid: Vibe and prism Pressure switching solenoid opens evaporative line between fuel tank and canister When solenoid closed, air is blocked from entering fuel tank side of system Off during engine warm-up Vacuum is blocked from fuel tank Pressure in tank rises Significant decrease in pressure only when switching solenoid On Solenoid is On during P0446 FTP sees pressure stabilize when PCM commands switch Off PCM sets P0446 if solenoid does not close Evaporative Emission System Tester (EEST): Tool number J41413-200 updates pressure purge diagnostic station Some 1996-1998, and all 1999 and newer cars and light trucks illuminate MIL when 1mm (.040 in) or greater leak is detected Some 2000 vehicles illuminate MIL at .5 mm (.020 in) or greater GM vehicles that meet new standard cannot be diagnosed with ultrasonic equipment J41413-200 introduces smoke into sealed EVAP system System leaks are located using white light Traces of smoke escaping from sealed EVAP system are detected 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 EONV replaces previous methods All other comprehensive component tests are still used during engine operation EONV will be introduced on some 2003 trucks and 2004 cars Monitors EVAP pressure with engine and key Off When performing parasitic draw test, it is normal to wait 40 minutes for PCM to power down EONV differences: PCM software modifications Canister vent solenoid wired to battery voltage instead of Ignition One EONV parameters: Ambient temp between 40 and 96° F Fuel level between 15 and 85% full Engine run time, distance traveled, engine coolant indicate system warmed up PCM enables only after trips with a cold start to ensure pressure Fuel tank pressure sensor was initialized Number of tests limited to prolong battery life Time between tests lengthened after a passed test EONV tests to ensure vaporization rates do not impact test results Volatility test runs after key down if all enable criteria was met PCM calculates pressure High fuel volatility - PCM aborts diagnostic Moderate fuel volatility - PCM performs diagnostic and corrects pressure result Low fuel volatility - PCM performs diagnostic, but does not apply corrections EONV sub-functions: Estimate ambient temperature PCM: Uses speed, airflow, and intake air temp to predict ambient temp PCM: Monitors fuel level and vacuum to detect refueling event Looks for abrupt change in vacuum Only looks for refueling events when vent is closed Performs a rationality test to determine if refueling was caused by intermittent signal Equates estimated ambient temp to intake air temp On-Board refueling vapor recovery (ORVR): Government mandated emission control system Prevents hydrocarbon vapor from escaping to atmosphere during refueling Vehicle fuel fill pipe smaller than on non-ORVR vehicles Liquid seal prevents vapor escape: Tank fills Fill limit valve closes off vapor line Tank pressure increases Backed up fuel covers nozzle aspirator, activating shutoff mechanism EGR System Operation Page 1 of 61PP-1pp340010 EGR system: Used to lower oxides of nitrogen emission levels Exhaust gas is fed back into combustion chamber, reducing: Combustion temperatures Oxides of nitrogen Too much EGR flow can cause a drivability concern Too little or no EGR can cause spark knock, overheating, or emission failure EGR valve controlled by high side driver (power side control) PCM controls 12-volt supply Powertrain control module: Uses "closed loop" strategy to control EGR valve Calculates desired amount of exhaust gas recirculation Commands pintle valve to move Sends pulse width modulated voltage signal to the valve Monitors EGR pintle position Adjusts command to make corrections Continual feedback and correction makes EGR system "closed loop" style Diagnostics: Tech 2 can command EGR valve Tech 2 shows actual position of pintle Positions can be selected When a desired position is commanded, actual position may fluctuate Wait a second or two for data parameter to stabilize Tech 2 display: EGR duty cycle displays a range from 0% to 100% Desired EGR position indicates pintle position commanded by PCM Actual EGR position indicates actual position of pintle EGR Feedback indicates fully closed or open valve EGR Position Error displays difference between desired and actual positions EGR Closed Pintle Position displays a value between 0 and 255 counts EGR Closed Valve Position will display voltage between 0v and 5v PCM uses voltage to determine if EGR fully closed EGR Flow Test Count indicates the number of test samples collected Advantages of high side PCM driver over linear EGR valves: Has more current carrying capacity Contains built-in diagnostic features Can signal microprocessor when fault is detected Contains recirculation diode to prevent EGR valve oscillations Note: Some linear EGR's are low side controlled. Refer to service information for your particular application. Secondary air injection system: Used to lower hydrocarbons and carbon monoxide PCM turns on AIR system during start-up AIR pump runs for one minute, supplying air through secondary air injection system into exhaust stream When PCM turns AIR pump off, de-energizes AIR solenoid valve AIR vacuum control: Solenoid controls AIR shutoff valves When system is enabled, control module provides ground to solenoid Enabled solenoid applies vacuum to AIR shutoff valves Check valve prevents backflow of exhaust gases into secondary air injection system Leak detection using soapy water solution Tech 2 and AIR system: Vehicle needs to be at operating temp and at idle Select Special Functions, Engine Controls, AIR System Monitor HO2S Sensor 1: Voltage should remain under 350 millivolts PCM may turn on AIR pump to perform diagnostics DO NOT command AIR system ON with engine not running - AIR pump can be damaged