Advanced Emissions and On Board Diagnostics OBD Chapter

Objectives • Describe the operation of on-board diagnostic systems • Explain the differences between OBD I and OBD II • Interpret OBD II scan tool data • Describe the operation of OBD II monitors • Use a scan tool to verify the running of various OBD II monitors © 2012 Delmar, Cengage Learning

Introduction • Government involvement in emission controls and fuel economy – Drives technology advancement • Objective of modern on-board diagnostics – Air-quality improvement – 90% of emissions occur during warm-up – Early computer-controlled: required 176°F to achieve closed loop – 1996: closed loop achieved at 68°F with OBD II within seconds of startup © 2012 Delmar, Cengage Learning

History of On-Board Diagnostics • 1988: OBD I legislation began with cars sold in California – California has toughest emission laws • Since 1994: air quality in Los Angeles basin has been improving • Today OBD legislation national – 1997: OBD II required on all cars built in U. S. © 2012 Delmar, Cengage Learning

OBD II Operation • OBD II detects exhaust and evaporative emissions in excess of 1. 5 times FTP • FTP measures emission in grams per mile – Hydrocarbon, carbon monoxide, and oxides of nitrogen • Extra hardware is required – Heated O 2 sensor and misfire detection capability – 16 -pin data link connector – Evaporative system monitor – Positive crankcase ventilation (PCV) monitor © 2012 Delmar, Cengage Learning

Society of Automotive Engineers (SAE) Standards • Standard communication protocol – Specifies protocol used to communicate between computer and scan tool • Standardization of terms – Lists common names for all components that serve a similar purpose • Standard diagnostic connector – Requires a universal DLC for reading DTCs • Generic scan tool – Scan tool used on different makes of vehicles © 2012 Delmar, Cengage Learning

Society of Automotive Engineers (SAE) Standards (cont'd. ) • Standard diagnostic trouble codes – SAE J 2012: SAE-approved list of generic DTCs • Common diagnostic test modes – Scan tools have global and enhanced portions – Enhanced side requires VIN input • Includes manufacturer-specific menus and data – Global is generic • Includes 15 modes • Only modes one through nine are used © 2012 Delmar, Cengage Learning

Trouble Codes and the Malfunction Indicator Lamp • MIL must illuminate if emissions exceed 1. 5 times the federal standard – OBD II deals only with emission codes – Generic scan tool might read 50 fault codes • Manufacturer’s tool might read hundreds – DTC is stored in computer’s non-volatile RAM – Warm-up cycle occurs every time the engine cools off and temperature rises 40°F • Code erased after 40 warm-up cycles © 2012 Delmar, Cengage Learning

Trouble Codes and the Malfunction Indicator Lamp (cont'd. ) • Trip requires ignition switch to be off for a while – Emission control monitors operate to complete one trip • Enabling criteria include monitors – Engine misfire and catalyst efficiency – Fuel system – O 2 sensor – EGR – Evaporative system – Air injection © 2012 Delmar, Cengage Learning

Trouble Codes and the Malfunction Indicator Lamp (cont'd. ) • During drive cycle engine must enter closed loop – All trip monitors must operate • Same fault must be detected during two drive cycles to light MIL – First time DTC enable criteria are met: pending code is set – Second consecutive occurrence of the fault illuminates the MIL • Some scan tools read pending codes © 2012 Delmar, Cengage Learning

OBD II Codes • DTCs have five characters – First character: letter that identifies the area of the vehicle – Second character: zero is generic and one is assigned by manufacturer – Third character: one to eight represents vehicle subsystem – Last tow characters: represent the fault code © 2012 Delmar, Cengage Learning

OBD II Codes (cont'd. ) • Expanded numbers – P 2 XXX and P 3400–P 3999 • Types of DTCs – Two emission related and two are not • OBD are separate programs within the computer – Computer decides which signals are rational © 2012 Delmar, Cengage Learning

OBD II Diagnostic Testing • Monitors look for malfunctions – Continuous: operates when engine runs – Non-continuous: tests once per drive cycle • Readiness indicators – Tell if OBD II monitors completed since KAM last cleared • Incomplete monitors result in failed test © 2012 Delmar, Cengage Learning

OBD II Diagnostic Testing (cont’d. ) • Monitor tests – Comprehensive component monitor • Continuous monitor • Looks at electrically controlled emissions devices – Evaporative emission leak check monitor • No leaks larger than end of a ballpoint pen • Done by pressure or by vacuum – EGR monitor • Checks electronic components that direct vacuum or measure opening of the EGR valve © 2012 Delmar, Cengage Learning

OBD II Diagnostic Testing (cont’d. ) – Fuel trim monitor • Operates continuously when fuel system in closed loop • Compares fuel trim to O 2 sensor signal – Heated oxygen sensor monitor • Changes the injector pulse width while checks upstream oxygen sensor • Checks for fast enough oscillating frequency © 2012 Delmar, Cengage Learning

OBD II Diagnostic Testing (cont’d. ) – Sensor identification • O 2 sensor is identified by code resulting from monitor test – Oxygen sensor heater monitor • Tested electronically • Tests right away in drive cycle – Misfire detection monitor • Continuously detects when engine slows momentarily due to misfire – Type A misfires • PCM is more likely to flash the MIL © 2012 Delmar, Cengage Learning

OBD II Diagnostic Testing (cont’d. ) – Type B misfires • Typical monitor allows two- to three-percent random misfiring • After one more drive cycle, a code is set – Secondary air injection monitor • Higher engine compression increases NOX, which provides more O 2 for conversion in the cat • Test is done at startup when air is needed – Thermostat monitor • Used since 2000 model year • Enabled in drive cycle after engine is off two hours © 2012 Delmar, Cengage Learning

OBD II Diagnostic Testing (cont’d. ) – Positive crankcase ventilation system monitor • Required since 2004 model year • Detects disconnected, damaged hose, or restriction in hose or valve – Catalytic converter monitor • Other monitors must run before catalytic converter monitor runs • Detects switch ratio – Mode $06 Data • Tells which tests have been run • Test results © 2012 Delmar, Cengage Learning

Emission Testing Programs • Enhanced testing – Used in areas with higher smog levels • Rich or lean conditions must be addressed before diagnosing NOX failures – Lean air-fuel ratio increases NOX when it causes preignition • Rich mixture does not increase NOX but resulting misfire increases CO • O 2 S must be fast enough in repeated transitions from rich to lean and must be within calibration © 2012 Delmar, Cengage Learning

Emission Testing Programs (cont'd. ) • Propane enrichment test – Run at 2, 000 -2, 500 rpm for one second – Shut off propane while system is still rich – DSO reading should flatline lean – Inject a quick burst of propane while pattern is lean – Voltage should rise from lean to full rich in less than 100 ms © 2012 Delmar, Cengage Learning