Transcript Chapter 25

Chapter 25
Detailed Diagnosis and Sensors
© 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
© 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
© 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
© 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
© 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
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Monitor Failures
• Sensor or sensor circuit
faults can prevent a
monitor from running
or passing
• Check monitor status as
part of inspection
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
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
© 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
© 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?
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Symptom-Based Diagnosis
• 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
© 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
© 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
© 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
© 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
© 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
© 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
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Electrical Noise
• Poor grounds allow
RFI
• Small changes in
signals
• Can be on either
power or ground
© 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
© 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
© 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
© 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.)
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Engine Coolant Temperature (ECT)
Sensor
• Used for:
– Fuel injection
– Ignition timing
– Variable valve timing
– Transmission shifting
– EGR
– Canister purge
– Open/closed loop
© 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
© 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
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 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 switches can be checked
with an ohmmeter or voltmeter. Technician B
says temperature sensors can be checked with
an ohmmeter. Who is correct?
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
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
© 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
© 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
© 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
© 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
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 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 a MAF Sensor
• Testing varies on vehicle
• Checks induction
system for leaks
• Some produce a digital
frequency signal
• Faulty MAF can cause
lean conditions
© 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 (O2S)
• 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
© 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
© 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 (TiO2) 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
© 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
© 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
© 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 HO2S operation?
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Checking O2 Sensors and Circuits
• Things that can cause an O2 sensor to appear
faulty:
– Incorrect fuel pressure
– Malfunctioning AIR system
– EGR leak
– Leaking injector
– Vacuum leak
– Contaminated MAF sensor
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Identifying the Cause of O2 Sensor
Contamination
•
•
•
•
Examine engine for leaks
Check vehicle service history
Inspect for RTV use
Remove and inspect the sensor
© 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
© 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
© 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 (HO2S)
• To generate an accurate signal, the sensor
must operate at 750°F (400°C) or higher
• Current HO2S have a built-in heating element
• The PCM controls the heater ground
© 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 (ZrO2) Sensors
• Monitor voltage
and switching time
with a scan tool
• A DMM can be
used to watch
sensor voltage
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
HO2S Testing (Cont.)
• Upstream HO2S voltage should have at least
seven cross counts in five seconds at 2500
RPM
• Downstream sensors may have fewer cross
counts
© 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
© 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 HO2S 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
HO2S 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
© 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
O2 sensor can cause incorrect sensor readings.
Technician B says both pre- and post-catalyst
O2 sensors should cycle rapidly between rich
and lean. Who is correct?
© 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
© 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
© 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
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Accelerator Pedal Position Sensor
• 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
© 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
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
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
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Knock Sensor (KS)
• Converts knock
vibration into a
voltage
• Mounted in block,
intake, or cylinder
head
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Computer Outputs and Actuators
• 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 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
• 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
© 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 Actuators
with a Lab Scope
• 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
© 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
© 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
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.