Transmission Control Module (TCM)

What Is a
Transmission Control Module for a Car?


By Katina Blue, eHow Contributor


A transmission control module uses computerized technology
to regulate shifting.


The transmission module
is a computerized auto part that controls shifting on vehicles with automatic
transmissions.


1. Gear
Changes


The
transmission control module receives data from the engine control unit that it
uses to regulate when and how a vehicle changes gears.


2. Sensor
Controls


Signals are
sent from sensors to the transmission control module. In return, the module
sends signals to the lock-up clutch, a mechanism that regulates fuel efficiency
and power.




3. Memory


Because the transmission module is
computerized, it can store various information about a vehicle's transmission
system. It uses the stored information
to adjust shifting according to driving conditions.




4. Symptoms


A faulty
transmission module can cause a delay in acceleration when the gas pedal is
pressed. Also, when the car is shifted into drive, it may sound as if it is
still in neutral.





Article 1:


What Causes
a Control Module on a Vehicle to Go Bad?


By Marcus
Baker, eHow Contributor





A control
module can prevent you from driving if it goes bad.


The control
module of a vehicle is basically the computer that does the thinking for an
engine's control system. It affects the functioning of things ranging from a
vehicle's charging system to its transmission. This is why when the control
module goes bad, the engine suffers functionality issues as well.





1.1 Voltage Overload


One of the
main things that can cause a control module on a vehicle to go bad is voltage
overload. This can occur when a short exists in the circuits of either a
solenoid or actuator. Replacing the control module will do no good if these
shorts are not dealt with as the replacement control module will experience
voltage overload as well.




1.2 Water


Another
thing that can cause a vehicle's control module to go bad is water. Circuits
get shorted out and the control module's electrical connections are harmed from
the corrosion that builds if water manages to reach the inside of the control
module. This is why repairs are usually not even attempted on control modules
that come out of flooded vehicles.


1.3 Vibration and Stress


Vibration as
well as thermal stress has also been known to cause control modules to go bad.
This is because they can cause tiny cracks to form in the control module's
circuit boards. However, unlike water damage, this type of damage to a control
module is repairable.





Article 2:





Automatic Transmission
Fluid Share




2.1 SMELL




Watch out
for ‘pink stink’, the burned odour that indicates trouble inside an automatic
transmission. The next time you check your ATF, sniff the fluid. If it smells
like burned toast and/or has a discoloured brown appearance, the fluid has
cooked itself and is no longer capable of providing proper lubrication to the
transmission. If you are lucky, you may have caught the problem before serious
damage has been done – but more often than not by the time the fried fluid is discovered,
the transmission is also toast.




2.2 PARTICLES




Compared to
engine oil, ATF has live pretty easy. There is no soot, gasoline, or
condensation from combustion blowby to contaminate the fluid. The only physique
contaminants the fluid must deal with are the particles that wear off the
friction plates, gears and bearings inside the transmission. Most transmissions
have some type of internal filter to keep the fluid clean. (Chevrolet Aveo has,
however, our gearbox in Cruze is concealed – so we don’t know there is or not)




2.3 HEAT




Heat is the
main concern for ATF. Auto transmissions create a lot of friction, and friction
produces heat. The fluid is constantly churning inside the torque converter and
being pumped through metering orifices and hydraulic circuits. Every time the
tramission shifts gears, the clutch packs generate even more heat that must be
carried away by the fluid. The greater the load and stress on the transmission,
the more heat it generates and the hotter the fluid gets.





From the
discussions with Spore Cruzers;




Based on
their experience, some encountered TCM problem and some encountered gearbox
problem. Well, we did not really know which the real cause is as the car was
sent in to the SC and they just changed the gearbox entirely. There is no
explanation from the SC as to why it happened. According to one of them (also a
car mechanic who drives Cruze), he demanded to check the ATF, but of course the
SC claimed that the ATF is a long life ATF that does not need to be changed.
However, he insisted. The moment when the ATF is drained out, he realized that
the ATF is black. (The real colour of ATF should be TRANSPARENT PINK).




So here are
very simple analysis, and let us think for ourselves in a more logical point of
view.




1. Is the ATF really long life? We
would not choose to believe that ATF is long life as it turned colour.




2. How much heat can the ATF resist in
the gearbox? We would not know.




3. The gearbox we use in Cruze is the
same as Opel Astra, they are told to change ATF every 40000km, why are ours
considered long life? Spore Cruzers suggest changing ATF at every 20,000km due
to our climate and also depends on our driving condition.




4. We stay in a tropical region where
humidity level is high, can the ATF last? High humidity level often causes
things not to last long.




5. Our driving behaviour and traffic
condition plays a very important role too. Do we tract or rev our cars? Do we
shift gears often? Are we a city driver who are always stuck in the traffic or
a highway driver? City driving with constant gear shifts tend to stress gearbox
more and therefore, heat accumulation is higher. Highway driving stresses gears
lesser as there are lesser gear shifts. If you are stuck in a traffic jam and
car is not moving, please shift to NEUTRAL, this will cut down the heat as well
as to help save fuel consumption.




6. Some car owners would argue that
they seldom use their cars or only drives around urban area and breaks down, to
me (my own self), the lesser you use your car the more problem you may
encounter. I have used my Aveo (8 years old) on a lot of highway usage with
170,000km now and still no parts falling apart, except for wear and tear. (You may
choose not to believe me but highway drivers or high usage of cars are less
likely to break down, just imagine our own body, if you exercise regularly, the
less chance you get sick – it is the same theory)




Spore
Cruzers’ answer to the problem;


There is a component in the
gearbox. The component is SOLENOID. SOLENOID is to control Gear Shifts. When
the heat is too much, it short-circuits the TCM. What causes the heat is the
failure of ATF’s function. (refer to Article 1.1 and Article 2.3) That may be why
TCM is hot.(short-circuit)


How the
Spore Cruzers change ATF?




Step 1:
Drain the ATF out until the last drip.




Step 2:
Refill 5 litres (the amount is a guideline)


– Best to refill the same as what is
drained out.


(our gearbox
is 7 litres, after draining the ATF, there will be about 2 litres trapped in
the torque converter with contaminants)

Step 3:
After the refill, drive your car for 100 – 200 km (only a guideline), the
trapped

2 litres ATF will then already
mixes with the new 5 litres new ATF.




Step 4:
After 200km of driving, drain out 2 litres ATF (use a container to measure)




Step 5: Top
up 2 litres. (Done)


---------------------------------------------------------------------------------------------------------


For lazy
cruzers or if you decide to have a constant change at 20000km, step 1 and step
2 will do. Not necessary to do step 3, 4 and 5. (Complete step 1 to 5 will give
the gear cleaner change)




*Please
observe your ATF condition during the process of changing. I personally never
leave the mechanic to do himself. Don’t even know what would happen to your car
next.




**For
Malaysian Cruzers who encounter TCM problem, not only your TCM is changed, the
SC also change the ATF inside your gearbox. Do you know that? Why must they
change the ATF if it is in good condition?




***I have
also received a stupid reply when I did a research in one of the SC, that
mechanic told me that ATF in the gearbox is definitely black and it is normal.
STUPID ANSWER!




****A note
to ATF change: How much of ATF is drained out, you must top up the same amount.
Less ATF will cause overheating and jerk, too much will cause blockage.


*****We are
using a 7-litre gearbox, 4 litre ATF change is not sufficient





Gearbox
without dipstick


Unfortunately
we do not have a dipstick for our gearbox. To check the fluid level, the
transmission must be warm and the vehicle must be parked on a leveled surface.
When the fill plug is removed, some fluid should dribble out of the hole if the
fluid is at the proper level (flush with the bottom of the fill plug hole). If
no fluid comes out, it may be a sign of decreasing ATF.


Try to also
smell from the plug if there is any burnt smell.(Article 2.1 Smell)











ATF on tissue
extracted by a dipstick from another car. Dipstick to touch the visible
component to make sure there is ATF. (Colour: Pink with a little black residue,
Mileage 8900km) Also, fluid flush on the fill plug.



The above articles, discussions and
researches are only references. Each and every individual Cruzer must act
accordingly to his/her own discretion as all driving conditions and the
environment we are in are different. We are not sure of the definite problems or
causes, therefore, information gathered are based on the sources we could find
and troubleshoot since we are not correctly assisted by the SC.





Tea 05/08/12

Hi Chuang Chee, there have been a discussion esp among 2010 batch owners about whether to proceed to change ATF immediately or wait until TCM gives in and have it replaced under warranty (ATF will only be changed according to schedule approriately thenafter). There are pros and cons for each approach, which are as below:

OPTION 1: Change ATF immediately
Pros: you may prolong the TCM life by changing the ATF before it affect TCM
Cons: If the TCM is already affected, it'll just be a waste of money as TCM will still need to be replaced. Please note that there is no early symptom for it to occur (SC will only confirm TCM got issue if based on their diagnosis on the car) so your safest bet is to ask them to run diagnostic test first, and decide if you want to proceed to change ATF

OPTION 2: Wait until issue occur, change TCM (and ATF) and proceed with regular ATF maintenance after that
Pros: It is covered under warranty so no additional cost. Plus you'll be able to start your ATF maintenance from 0, knowing that the TCM is in good condition to begin with.
Cons: You'll never know when the TCM will be faulty so it'll be quite a worry especially if you'll be having a long journey drive, or during emergencies. Plus there are various kind of things happening when the TCM issue happens, and some of them (the serious ones) may pose a risk to you or other people on the road. In addition, there may be delay in replacement especially if there is no stock

I personally have changed my ATF at 33k (mainly due to my wories of having it fail during Raya holiday), and plan for the next replacement at 50-60k (maybe 50k as 60k service cost alone would be around 1.2k)

thx for d goood advise..
i am aso thinking of jz changing the ATF..
but in case my TCM broke down after 3 years...will i need to pay to get it replaced??

chuangchee wrote:thx for d goood advise..
i am aso thinking of jz changing the ATF..
but in case my TCM broke down after 3 years...will i need to pay to get it replaced??

After the warranty period is over, yes you need to pay for it