1. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Chapter 25 Detailed Diagnosis and Sensors

2. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Using Scan Tool Data Retrieve DTCs Visual inspection Service information Monitor failures Freeze frame data Mode 6 data

3. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Diagnostic System Check Checks for module communication Retrieve DTCs Check for aftermarket accessories Visual inspection

4. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Connecting the Scan Tool Turn ignition off Install correct cable or DLC connector Connect to the DLC Turn on and configure the scan tool

5. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Quick Tests Used on Ford products Retrieves KOEO and KOER DTCs

6. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Parameter IDs (PIDs) Identify which pieces of data are requested from the module PIDs are the same on each vehicle Not all vehicles support the same PIDs

7. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. DTCs and Service Information Locate code description Determine code setting criteria Research TSBs and software updates Follow pinpoint tests

8. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

9. Monitor Failures Sensor or sensor circuit faults can prevent a monitor from running or passing Check monitor status as part of inspection

10. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

11. Freeze Frame Data Freeze frames stored when DTC is set Contains specific PID values at time of DTC setting Freeze frames may be overwritten by a higher priority DTC Often useful to “drive the freeze frame” to verify fault and repair

12. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Mode $06 Data Access to monitor test values Can be used to check component operation and misfire rates May need to be decoded to be useful

13. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Knowledge Check What is the difference between a DTC and a PID?

14. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Visual Inspection Wiring and vacuum hoses Aftermarket accessories Battery condition Coolant level Exhaust leaks

15. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Before diagnosing symptoms, ensure: – ECM and MIL are operating correctly – No stored DTCs – Scan data within normal ranges – Scan tool to OBD system communication – No TSBs for current symptom – All ECM/PCM grounds are correct – Vehicle modifications identified Symptom-Based Diagnosis

16. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Common Symptoms Hard start/long crank hard start – Cranks normally but does not start quickly No crank – Starter does not turn engine over No start (engine cranks) – Engine turns over but does not start even after prolonged cranking

17. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Common Symptoms (Cont.) Slow return to idle speed Fast idle or runs on (diesels) Rough or unstable idle and stalling Low/slow idle or stalls/quits during acceleration Backfire

18. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Common Symptoms (Cont.) Lack of or loss of power Cuts out, misses Hesitation or stumble Surges Detonation/spark knock Poor fuel economy

19. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Basic Testing Ohmmeter Checks – Can check temperature sensors, relays, coils, and motors

20. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Basic Testing Voltmeter Checks – Voltage to and from sensors

21. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Basic Testing Lab Scope Checks – Voltage signals and current draw waveforms

22. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Testing Sensors All sensors detect a condition and change it into an electrical signal Sensors may be: – Switches – Variable resistors – Voltage or frequency generators – Some inputs are simply connections from other modules or battery voltage and ground

23. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

24. Diagnosis of Computer Voltage Supply and Ground Wires Verify the power and ground circuits to the ECM/PCM Check power and ground circuit voltage drop Good ground circuits is critical for all reference voltage sensors

25. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

26. Electrical Noise Poor grounds allow RFI Small changes in signals Can be on either power or ground

27. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Clamping Diodes Used to limit high voltage spikes Prevents spike from reaching computer

28. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Switches Either normally open or normally closed Send digital signal to the PCM Some are provided with a reference voltage Can be on ground or power circuit

29. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Testing Switches With an ohmmeter With a voltmeter Some switches are adjustable

30. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Testing Switches (Cont.)

31. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Temperature Sensors Most are NTC thermistors – High resistance cold – Low resistance hot PCM supplies 5 volts reference Voltage changed by sensor Signal returns on the ground wire

32. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

33. Engine Coolant Temperature (ECT) Sensor Used for: – Fuel injection – Ignition timing – Variable valve timing – Transmission shifting – EGR – Canister purge – Open/closed loop

34. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Intake Air Temperature (IAT) Sensor Used for fuel and spark calculations On MAP equipped engines the IAT is in an intake air passage Can be integral to MAF sensor Used with ECT to determine cold start

35. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Other Temperature Sensors Cylinder head temperature (CHT) sensor Engine oil temperature (EOT) sensor Fuel rail pressure temperature (FRPT) sensor EGR temperature sensor

36. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Testing Scan tool values Highest possible value = short in circuit Lowest possible value = open in circuit Place in water Never apply an open flame to a sensor

37. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

38. Knowledge Check Technician A says switches can be checked with an ohmmeter or voltmeter. Technician B says temperature sensors can be checked with an ohmmeter. Who is correct?

39. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Pressure Sensors Most are piezometric sensors The amount of flex dictates the voltage signal One side exposed to reference pressure and other to a calibrated pressure or vacuum

40. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

41. MAP Sensors Sense air pressure in the intake manifold Not significantly affected by altitude or barometric pressure Intake pressure varies based on engine speed and load Used to calculate fuel delivery

42. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Testing MAP Sensors Can cause rich, lean, or surging conditions Check vacuum supply PCM supplies 5 volt reference and ground MAP can be monitored with scan tool Frequency output can be scoped

43. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Barometric Pressure (BARO) Sensor Used on some engines to alter fuel and ignition timing based on altitude Higher elevations have less atmospheric pressure Often located in PCM and not separately replaceable

44. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Vapor Pressure Sensor (VPS) Measures vapor pressure in EVAP system Responds to slight changes May be mounted on fuel pump or remotely Remote sensors have hose connections Check hoses and connections

45. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Other Pressure Sensors Feedback pressure EGR sensor – How much the EGR valve is open Fuel rail pressure sensor – Used to adjust injector pulse width Turbo or supercharger pressure sensors – Monitors boost pressures

46. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Mass Airflow (MAF) Sensors Measures air entering the engine Used to calculate engine load Sensors are placed between air cleaner and throttle plate Common MAF sensor is the hot-wire sensor

47. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

48. Testing a MAF Sensor Testing varies on vehicle Checks induction system for leaks Some produce a digital frequency signal Faulty MAF can cause lean conditions

49. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Oxygen Sensors (O 2 S) Used to ensure correct air/fuel ratio for catalytic converter OBD II requires pre and post converter sensors Generate voltage based on oxygen content in the exhaust Lean = low voltage, rich = high voltage

50. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Heated Oxygen Sensors Required to get sensor operating as quickly as possible Both sensor and heater circuits are monitored for correct operation

51. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Titanium Dioxide (TiO 2 ) Sensors Do not generate voltage Alters a 5 volt reference signal Low oxygen content equals low voltage, below 2.5 volts High oxygen content equals voltage above 2.5 volts

52. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Air/Fuel Ratio (A/F) Sensors Changes current in the circuit Can be used in very lean conditions At stoichiometric, no current is generated and the voltage detection circuit is 3.3 volts When rich, there is negative current flow and voltage is below 3.3 volts

53. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. A/F Ratio Sensor Data

54. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Knowledge Check How does A/F ratio sensor operation differ from traditional HO 2 S operation?

55. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Things that can cause an O 2 sensor to appear faulty: – Incorrect fuel pressure – Malfunctioning AIR system – EGR leak – Leaking injector – Vacuum leak – Contaminated MAF sensor Checking O 2 Sensors and Circuits

56. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Examine engine for leaks Check vehicle service history Inspect for RTV use Remove and inspect the sensor Identifying the Cause of O 2 Sensor Contamination

57. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Testing with a Scan Tool OBD II system checks pre-converter sensors for faults, response rate, and heater circuit operation Voltage should toggle between 0.2 volts to 0.8 volts

58. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Scan Tool Graphing

59. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Heated Oxygen Sensors (HO 2 S) To generate an accurate signal, the sensor must operate at 750°F (400°C) or higher Current HO 2 S have a built-in heating element The PCM controls the heater ground

60. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Zirconium Dioxide (ZrO 2 ) Sensors Monitor voltage and switching time with a scan tool A DMM can be used to watch sensor voltage

61. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Testing with a Lab Scope

62. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

64. HO 2 S Testing (Cont.) Upstream HO 2 S voltage should have at least seven cross counts in five seconds at 2500 RPM Downstream sensors may have fewer cross counts

65. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Sensor Switch Rate

66. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Air/Fuel Ratio (A/F) Sensors Cannot be tested same way as HO 2 S sensors PCM supplies 3.0 volts to one wire and 3.3 volts to other wire Use a scan tool that can read A/F sensor PID Large changes in air/fuel ratio will toggle voltage readings Can also use an ammeter in series

67. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. HO 2 S and A/F Repair Do not attempt to repair wiring, connector, terminals, or sensor assembly Do not apply cleaners to sensor or wires Wiring should not be sharply bent or kinked Use the proper sensor socket tool

68. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Knowledge Check Technician A says an exhaust leak before the O 2 sensor can cause incorrect sensor readings. Technician B says both pre- and post-catalyst O 2 sensors should cycle rapidly between rich and lean. Who is correct?

69. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Position Sensors TP Sensors – Provides rate of opening and position – Three wires TP Sensors for electronic throttle control – Uses two resistors in one housing

70. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Electronic Throttle Control

71. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Testing Position Sensors Check voltage reference and ground Check resistance Connect a lab scope and watch pattern as throttle is opened and closed

72. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. EGR Valve Position Sensor Most are linear potentiometers Have a 5 volt reference, voltage signal, and ground wires Can be checked with a DMM or lab scope similar to a TP sensor

73. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Similar to TP sensor operation, uses two potentiometers PCM determines power or torque demand The PCM then commands the throttle plate motors to open or close as needed Accelerator Pedal Position Sensor

74. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. APP Data

75. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Speed Sensors Vehicle speed sensor Can be either a magnetic pulse generator or hall-effect sensor Provides a waveform proportional to vehicle speed Used for cruise control, EGR, EVAP, transmission, and torque converter

76. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

77. Troubleshooting a VSS Check wiring and connections Can be tested with a scan tool or lab scope VSS can be checked with the vehicle on a hoist

78. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Position/Speed Sensors Crankshaft position (CKP) sensor – Used for misfire detection – Can be checked with scan tool or lab scope Camshaft position (CMP) sensor – Used for fuel injection control

79. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

81. Knock Sensor (KS) Converts knock vibration into a voltage Mounted in block, intake, or cylinder head

82. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Air management solenoids Evaporative emissions system purge valve EGR flow solenoid or EGR valve Fuel injectors Fuel pump Idle speed controls Ignition module Warning lights Other solenoids Electronic throttle control Computer Outputs and Actuators

83. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.

84. Electronic Throttle Control Interprets throttle movement for precise throttle control One or two position sensors are used Adaptable to cruise control and traction control systems Can be tested with scan tool and DMM

85. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Most computer-controlled circuits are ground controlled The PCM energizes the actuator by providing the ground Understand what the actuator is before trying to test Some are pulse width controlled Testing Actuators with a Lab Scope

86. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Testing With A Scan Tool

87. © 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part. Repairing The System Once repaired, verify the repair Road test the vehicle If applicable, make sure the monitor runs and passes