Diagnostic
procedure
Training for the future
Diagnostic Procedure
So, where do we
start?
Training for the future
Diagnostic Procedure
Listen to the customer complaint
So, where
do we
start?
Listen to the car’s complaint
Loaded electrical light check
Carry out basic checks
Check battery supplies
Whilst car running
Measure voltage
Post to post
DC voltage 14.2 v
AC voltage must be less
then 0.3 volts
Training for the future
Diagnostic Procedure
Listen to the customer complaint
So, where
do we
start?
Listen to the car’s complaint
Loaded electrical light check
Carry out basic checks
Check battery supplies
Check battery grounds
Disable car from start
Measure voltage drop
(whilst cranking)
All must be
less then
0.3 volts
Block
Negative
Post to …
Chassis
Clamp
Training for the future
Diagnostic Procedure
Listen to the customer complaint
So, where
do we
start?
Listen to the car’s complaint
Loaded electrical light check
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
Obtain technical information
So, where
do we
start?
Supplies
inputs
electronic
control module
outputs
grounds
Keep customer informed of progress
Prepare invoice
Diagnostics
R and R
Inform customer of final budget
Training for the future
Diagnostic Procedure
Diagnostic tools!
Training for the future
Diagnostic Procedure
Scan tool
Diagnostic
tools
Understanding DTC - P0123
P
B
C
U
0
1
Powertrain
Body
Chassis
Communication
Code ID
Generic
Manufacturer specific
1- 8 Specific area of concern
Training for the future
Diagnostic Procedure
Oscilloscope
Diagnostic
tools
So, you want to measure an injector
pattern
Back emf
Supply Voltage
Pintle bounce
Ground
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
TPS (input)
TPS input
AF input
electronic
control
module
Throttle body
Ecm controls
output timing
injection etc
Accelerator
peddle
Cable controls butterfly
Training for the future
Diagnostic Procedure
How does
the system
work?
Throttle control
Electronic
throttle control
TPS
(feedback)
Electronic
accelerator
peddle
electronic
control
module
M
Ecm controls
motor
(butterfly)
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
+ volts
+ volts
time
Pre Cat
Ox sensor
time
Post Cat
Ox sensor
Catalytic
converter
Training for the future
Diagnostic Procedure
Sensors
How does
the system
work?
+ volts
Magnetic
time
- volts
volts
Optical
time
volts
Hall Effect
time
Training for the future
Diagnostic Procedure
How does
the system
work?
Current limiting
No current limiting (ign coil)
Linear current limiting (ign coil)
Switched current limiting (injector)
Training for the future
Diagnostic Procedure
Differential amplifiers
How does
the system
work?
electronic
control
module
+
Inverting and non
inverting Inputs
+ volts
time
electronic control
module
+ volts
+
time
Training for the future
Diagnostic Procedure
Should this
component
fail what
will the
symptom
be?
TPS
If there was a sudden drop
in voltage?
tps
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Diagnostic Procedure
Injector
Should this
component
fail what
will the
symptom
be?
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 module
Good current limiting
Uncontrolled oscillation
bad current limiting
Training for the future
Diagnostic Procedure
Should this
component
fail what
will the
symptom
be?
Ox Sensor
Lazy Ox sensor
Bad earth
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
Body control unit
Electronic cont mod
Training for the future
Diagnostic Procedure
Reading
technical
information
Should one of these components
fail
How will it relate to customer’s
complaint?
Supplies (DC & AC)
inputs
electronic
control module
outputs
grounds
Training for the future
Diagnostic Procedure
Reading
technical
information
Charging systems
Ignition ON Engine running
Ignition off
System
shut
down
Ignition off
Engine starts
Cranking
Training for the future
Diagnostic Procedure
What is CAN
bus?
Non - CAN
bus
systems
Hard wired
ect
ecm
dashboard
tcm
(conventional
system)
air con
other
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Diagnostic Procedure
Sharing of information
Similar to a Fax machine
Puts a message on the ‘BUS’
Other control units share information
What is CAN
bus?
ect
CAN bus
systems
It is NOT unilateral
It is ‘Bidirectional’
ecm
dashboard
tcm
air con
other
Training for the future
Diagnostic Procedure
How to diagnose
What is CAN
bus?
DTC
Myriad of DTC’s – which one would you tackle first?
Must decipher which control unit is
‘logging’ the DTC code
ecm
CAN bus
systems
dashboard
tcm
air con
Training for the future