We will
divide this training into three sections to make it easier for the reader. The
sections will be as follows
Part One
: the common types of failure in ECU
Part tow
: The methods of programming in ECU
Part
Three : programming the ECU by diagnostic port OBD II
Before
starting, we will provide a comprehensive and brief introduction to understand
some of the elements and how they work in ECU.
Automotive computer
Receives
input data.
Perform
calculations.
Sends
output signals.
Stores
information.
Its internal components are:
1. Input
interface.
Receives
signals from sensors.
Converts
digital signals for the CPU.
2. Output
interface.
Convert
digital signals into applicable form for sensor.
3. Central
processing unit.
Receive
the data.
Do the
calculations.
Respond
according to the program.
Send
responses.
4.
Storage memory.
Read-only
memory (ROM)
Stores
most of the basic information
Can't be
changed
Programmable
read-only memory (PROM)
Can be
changed
Sometimes
called Flash E-PROM
Random
access memory (RAM)
Data is
temporary
Called
when required
It may be
overwritten.
5.
Electrical components.
An ECU is basically made of hardware and software
(firmware). The hardware is made of various electronic components on a PCB. The
most important component is a chip microcontroller together with an EPROM or a
Flash memory chip. The software (firmware) is a lower level set of codes that runs
on the microcontroller.
The ECU is characterized by:
Several analog and digital I/O lines (high and low
power).
Power interface/control device.
Different communication protocols (CAN, KWP-2000,
etc.).
large matrix switching for signals high and low
power.
Smart interface adapters communication
(standard or customized).
Automatic equipment recognition and enable
software sequence.
Power device simulation
TYPES OF FAILURES IN COMPUTERS AUTOMOTIVE
Automotive computer failures are divided into
two:
Physical failures.
Logical failures.
Physical Failures.
Caution: Computer components automotive are
extremely sensitive to electro-static discharges (ESD). Before handle any
component, make sure wear an anti-static bracelet or touch some grounded
object, such as a metal object, to eliminate any remaining static charge on the
body.
The static electricity of the human body, can irreversibly
damage circuits automotive computer integrations. Take precautions before
uncovering the ECU.
In the ECU we can find 5 types of failures physical
ones which have repair, the other faults possible is a damaged microcontroller,
but this components are custom made by the manufacturer with specific values,
which is Impossible to get a replacement in any store electronics. Fortunately
these components they are the last ones to be damaged.
The 4 faults that we find in a computer automotive
are the following.
1.Cracked or corroded weld point by rust. (This is a very common fault is 60% of Damaged ECUs are due to this cause.
2.Burnt track
3.Damaged transistor
4.Capacitor failures
5.Micro-processor Failure
1.Cracked or corroded weld point by rust
Although the cracks at the release points are
hardly noticeable, they must be repaired since they cause failure. It also
happens with points that show corrosion due to rust. This type of anomaly is
the cause of 60% of ECU failures.
But there is a question that comes to mind
regarding this type of damage. Are there
times when you can tell if the ECU has this type of failure without needing to
uncover it?. The answer is. Yes, there are times when we can know, when presents
one of the following two cases:
1.When there are times when the vehicle starts,
and there are also other times it does not to start for no reason .
2.When a fault occurs on the vehicle and then
disappear.
Only in these two cases can we be 100% sure. That
the problem lies in welding points that they are cracked. this does not mean
that this type of failures occur only in the two above cases. Which it means
that only in those two case we can be sure that the problem is a welding point cracked
or with rust corrosion. For all other cases which they may exist, they
necessarily you must perform a visual inspection.
Put the ECU on your table to open it, then
remove screws and the retaining clips.
The weak point of ECUs is that the solder
joints of the connectors soldered to the board are prone to cracking. This is
the most common failure that occurs.
The image on the left shows in this case a transistor
that presents this type of failure.
This image shows the solder joints on the back of plate.
All three weld points are cracked. It may not
seem like much, but this type of anomaly causes a momentary loss of connection.
Corrosion accumulates in these cracks. To verify if an ECU has this type of
failure, a visual inspection must necessarily be carried out.
A good repair involves heating the cracked
solder, removing the old solder, and then re-soldering it.
2.Burned track.
solution
This represents a fault, which is usually
solved with him making external bridges, in this case the solution would be to
weld a fine wire on the track burnt. In this case they must also replace all
capacitors electrolytics.
3.Damaged transistor.
First case:
Damaged output transistor.
Commonly the output transistors are the ones
that are damaged, these transistors are located in line, in which a heat sink
covers them. Pry each side a little at a time to remove it. Do not try to
remove the insulation at the same time as it may break.
You can now safely remove the insulation.
Here we have the output transistors, we proceed
to verify each one.
We proceed to check each transistor, all of
them must return equal values. For checked we proceed as follows.
First we check Base-Emitter:
Then we check Base collector:
To verify which transistor is damaged, the
values of each transistor are measured, and the one that gives a different
reading is the defective transistor.
Damaged 5v regulator transistor:
The procedure to verify if this type of transistor
is damaged, it is different from the case former.
This type of computer transistors automotive
are damaged when they have the following characteristics:
When it reads 0 Zero Ohms of a terminal to
another. (It is shorted between both terminals).
When it does not mark continuity from Base to Emitter
or Base to Collector on the X10 scale or from Emitter to Collector on the X10K
scale (in analog tester) (is Open Base to Emitter or Collector or from Emitter
to Collector).
When it marks continuity from Emitter to
Collector on the X10 scale. (Short-circuited from Emitter to Collector).
When it does not mark continuity from Base to
Emitter or from Base to Collector on a Digital tester on the scale to measure
Diodes. (Which is the scale used to measure Transistors in Digital testers).
It cannot mark both ways, that is, if the
transistor marks continuity with the negative test lead on one terminal and the
positive test lead on another terminal cannot indicate continuity if we
exchange the test leads. Because you can only score in one way, in one
direction so to speak.
NOTE:
The Transistor cannot mark continuity anyway,
nor can it not mark at all. The normal thing is From Base to Emitter, From Base
to Collector on the X10 scale and from Collector to Emitter on the X10K scale.
(I will explain it below.) You cannot mark from Emitter to Collector on the X10
scale. Otherwise it is damaged. (open from Emitter to Collector.)
Observation
When we talk about continuity, it is not refers
to Zero Ohms but to a measurement more or less, neither too low nor too high.
Normal Reading
Normal reading is when we place a test probe at
the Base of the Transistor and the other test lead is in the Emitter and the Collector
(first one and then the other.) and gives us a normal reading, that is, it does
not measure or zero or infinity, neither much nor little, etc. And if we
exchange the test leads, no mark nothing.
4.Capacitor failures
Note that the
title NOT ONLY refers to physically damaged capacitors, in power failures capacitors
we find two types:
1.Failures due
to UNDAMAGED Capacitors, but that have lost capacity.
2.Failures of
physically damaged capacitors.
Failures due
to lost capacitors ability
Always be wary
of electrolytic capacitors, especially if the ECU is more than 7 years old.
When you notice any burnt traces on the ECU printed circuit, proceed to replace
all the electrolytic capacitors. (ONLY ELECTROLYTIC CAPACITORS). Since it is
almost certain that they have lost capacity, and when not, having been directly
responsible for the failure, for little money we ensure its correct functioning.
Even if the
capacitor IS NOT DAMAGED, it You must proceed to measure your capacity, in this
way make sure it works perfectly.
Electrolytic
capacitors have a disadvantage. They tend to escape with age when exposed to
energy and heat cycles. Electrolyte leakage is very harmful to ECU boards. It
can actually eat away at the copper scraps and over time short out the board.
When that happens, the ECU will either stop working completely or act
strangely. As the capacitor leaks, it also loses its filtering properties,
possibly allowing harmful spikes in the ECU.
NOTE
Carefully
observe the polarity of the capacitor before removing it, to replace it exactly
the same. Many plates are poorly screen-printed and have the polarity reversed.
TAKE PRECAUTIONS IN THIS CASE.
Failures due
to physically damaged capacitors Damaged capacitors are very easy to recognize,
they are inflated at the top. Like the example in the figure.
Microprocessor failure:
The way to
verify if the microprocessor is damaged is through the diagnostic interface, in
this case we are using VAG_COM.
If the ecu manages to communicate with the
VAG-COM it means that the micro-processor is working perfectly, in case it can communicate
then it is damaged. A computer with a damaged microprocessor is very difficult
to repair since this part is custom designed by the manufacturer, which makes
it impossible. look for a replacement.
Important observation:
That there is communication between the vag com
and the ECU does not mean that the ECU is in good condition, it only means that
the microprocessor is working well, therefore we rule out failure in the microprocessor.
Logical failures
These types of faults are easier to repair and
do not require unclogging the ECU. We will start with a small introduction
about automotive computer communication protocols.
One more of the applications and capabilities
of computers is communication, and taking advantage of this characteristic, a communication
standard or protocol called OBD. (On Board Diagnostic).
OBD II is a standard that seeks to reduce the
levels of pollution produced by motor vehicles. OBD II is therefore not a electronic
injection system, but a set of standardizations that seek to facilitate the
diagnosis of vehicles. The OBD II standard is very extensive and is associated
with other standards such as SAE and ISO, so we are going to mention only the
most interesting parts such as:
DIAGNOSTIC CONNECTOR
It is a 16-pin type:
It must be located in the driver's area, under
the instrument panel.
Pin Description
2 - SAE VPW/PWM Communication
4 - Vehicle MASS
5 - MASSA Signal
7 - ISO 9141-2 Communication (K Line)
10 - PWM communication
15 - ISO 9141-2 Communication (Line L)
16 - BATTERY POSITIVE
COMMUNICATION WITH THE SCANNER
There are basically three types of
communication that can be used and are chosen by the manufacturer: SAE VPW -
variable pulse width modulation SAE PWM - pulse width modulation ISO 9141-2 -
CAN serial communication. These communication systems obey called
request-response patterns "communication protocol". Were detected the
following patterns used by the assemblers:
VPM – GM.
PWM – FORD.
ISO -- MITSUBISHI, NISSAN, VOLVO,
DODGE, JEEP and CHRYSLER.
DEFECT CODES
The format of the defect codes must have the
following presentation:
READINGS
In addition to fault codes, OBD II allows the
verification of various readings in real time such as: RPM, lambda probe, engine
temperature, engine load, MAP, vehicle speed, MAF, ignition advance, air
temperature, sensors after the catalyst, etc.
ON BOARD DIAGNOSIS
The primary objective of OBD-II is to help
quickly and effectively detect a failure in the injection system, with the sole
objective of minimizing vehicle gas emissions. When the system has some failure
in its operation, gas emissions increase beyond the limits, and this is the
mission of the standard. OBD-II establishes the forms and procedures for
detecting these faults.
For faults check and correct software faults we
use a scanner. We proceed to connect the scanner with the vehicle. We verify
that the ignition LED is on. The scanner is made up of its connector.
Likewise, a software that is responsible for detect
the different fault codes and delete them.
And they connect via Bluetooth to our personal
computer.
Then we open the switch
Once the switch is open we can verify the data
on the computer.
The software analyzes the vehicle's computer
and identifies the fault codes. The same program also erases the fault codes
that are generated, thus repairing the vehicle's computer.