diagnostic procedure training for the future. so, where do we start? diagnostic procedure
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Diagnostic procedure
Training for the future
So, where do we start?
Diagnostic Procedure
Training for the future
So, where do we start?
Listen to the customer complaint
Listen to the car’s complaint
Carry out basic checks
Check battery supplies Whilst car running
Measure voltage
DC voltage
AC voltage
Post to post
must be less then 0.3 volts
14.2 v
Training for the future
Diagnostic Procedure
Loaded electrical light check
So, where do we start? Carry out basic checks
Check battery supplies
Check battery groundsDisable car from start
Measure voltage drop (whilst cranking)
ClampChassis
Block
Negative Post to …
All must be less then 0.3 volts
Training for the future
Diagnostic Procedure
Listen to the customer complaint
Listen to the car’s complaint
Loaded electrical light check
So, where do we start? Carry out basic checks
Check battery supplies
Check battery grounds
Extract codes
Codes OBD I & OBD II
Inform customer
Obtain budget commitment
Training for the future
Diagnostic Procedure
Listen to the customer complaint
Listen to the car’s complaint
Loaded electrical light check
So, where do we start?
Obtain technical information
Keep customer informed of progress
Prepare invoice
Diagnostics
R and R
Inform customer of final budget
electronic control module
grounds
inputs outputs
Supplies
Training for the future
Diagnostic Procedure
Diagnostic tools!
Training for the future
Diagnostic Procedure
Understanding DTC - P0123
P PowertrainB BodyC ChassisU Communication
1 Manufacturer specific0 Generic
1- 8 Specific area of concern
Code ID
Diagnostic tools
Scan tool
Training for the future
Diagnostic Procedure
Diagnostic tools
Oscilloscope
So, you want to measure an injector pattern
Supply Voltage
Ground
Pintle bounce
Back emf
Injection Pulse width
Training for the future
Diagnostic Procedure
But, before one engages in diagnostic procedure, one must
understand how the system works and what the parameters ought to be (data list, waveforms, voltages,
current, resistance etc).
And above all 'should the component fail - what will the
symptom be?’
Training for the future
Diagnostic Procedure
How does the system work?
Throttle control
Conventional throttle control
electronic control module
Accelerator peddle Cable controls butterfly
TPS (input)
TPS input
AF input
Ecm controls output timing injection etc
Throttle body
Training for the future
Diagnostic Procedure
How does the system work?
Throttle controlElectronic throttle control
electronic control module
Electronic accelerator peddle
TPS (feedback)
Ecm controls motor (butterfly)
M
Training for the future
Diagnostic Procedure
How does the system work?
Sun-load sensor
Single zone
Dual zone
Training for the future
Diagnostic Procedure
How does the system work?
Catalytic converter
Pre Cat Ox sensor
Post Cat Ox sensor
Catalytic converter
time
+ volts
time
+ volts
Training for the future
Diagnostic Procedure
How does the system work?
Sensors
Magnetic
Optical
Hall Effect
time
+ volts
- volts
time
volts
time
volts
Training for the future
Diagnostic Procedure
How does the system work?
Current limiting
No current limiting (ign coil)
Switched current limiting (injector)
Linear current limiting (ign coil)
Training for the future
Diagnostic Procedure
electronic control module
How does the system work?
Differential amplifiersInverting and non inverting Inputs
+
-
electronic control module
+
-time
+ volts
time
+ volts
Training for the future
Diagnostic Procedure
Should this component fail what will the symptom be?
TPSIf there was a sudden drop in voltage?
tps
Training for the future
Diagnostic Procedure
Should this component fail what will the symptom be?
Injector
Good pattern at idle
Good pattern snap throttle
Good pattern back-off
Training for the future
Diagnostic Procedure
Should this component fail what will the symptom be?
Trigger moduleGood current limiting
Uncontrolled oscillation
bad current limiting
Training for the future
Diagnostic Procedure
Should this component fail what will the symptom be?
Ox Sensor
Bad earth
Lazy Ox sensor
Snap throttle
Closed loop
Good Ox sensor
Training for the future
Diagnostic Procedure
Should this component fail what will the symptom be?
Immobiliser
Electronic key Smart key reader
Electronic cont mod
Body control unit
Training for the future
Diagnostic Procedure
Reading technical information
Should one of these components fail
How will it relate to customer’s complaint?
electronic control module
grounds
inputs outputs
Supplies (DC & AC)
Training for the future
Diagnostic Procedure
Reading technical information
Charging systems
Ignition ON
Ignition off
CrankingEngine starts
Engine running
Ignition offSystem shut down
Training for the future
Diagnostic Procedure
(conventional system)
Hard wired
Non - CAN bus systems
What is CAN bus?
ect
ecm
tcm
air con
dashboard
other
Training for the future
Diagnostic Procedure
CAN bus systems
Sharing of informationSimilar to a Fax machinePuts a message on the ‘BUS’
It is NOT unilateral
Other control units share information
It is ‘Bidirectional’
What is CAN bus?
ect
ecm
tcm
air con
dashboard
other
Training for the future
Diagnostic Procedure
How to diagnoseDTC
Myriad of DTC’s – which one would you tackle first?
Must decipher which control unit is ‘logging’ the DTC code
CAN bus systems
What is CAN bus?
ecm
tcm
air con
dashboard
Training for the future
Diagnostic Procedure