Your driving along and suddenly the A/T light flashes up on your dashboard, you feel a clunk from the driveline. Don’t panic the light means there is a Diagnostic Trouble Code that has been logged within your vehicle control modules. Now you will notice the vehicle is down on power and not shifting gears, this is due to the vehicle now being in limp home mode.
What is limp home mode?
When the Mazda transmission control module enters limp home mode it switches the transmission into 3rd gear full time. This is why you feel the reduced power and the clunk of the gear change. It is not recommended to drive long distances in this mode hence the name “limp home” if you are near your home and the terrain is relatively flat it will be fine. If you are kilometers from anywhere pull over safely and cycle the ignition to see if the fault is intermittent and the light will self clear to allow you to continue home. If the light does not clear and your vehicle is permanently in limp mode you can call your road assistance and also call our office to arrange for your vehicle to be brought in for a diagnosis and quote.
Lost in communication with THE Transmission Control Module
Customers are always surprised when there is an electrical fault with their vehicle but think of our mobile phones most of us update them every 2-3 years. When compared to electrical components on your motor vehicles the modules are pretty reliable. One common issue we find on the Mazda 3 5 speed automatic transmission is a diagnostic code in the ECM and ABS modules which points to no communication between the Transmission Control Module.
What is a U code? U0101 - Lost Communication with TCM
Diagnostic codes normally have a letter prefix at the beginning and in this case, it is a U. This means the code is related to a communication issue across the vehicle’s communication network. Think of your home internet network if there was an issue between your Home PC and your Router if your dog pulled the ethernet cable it would show a communication issue on your home network.
Diagnosing your Mazda U0101 code.
A full diagnostic on the modules will need to be carried out with our diagnostic scanner to confirm the trouble codes in your modules. Then looking up the wiring diagrams for your vehicle we can then confirm the modules are powered and also have the correct communication signals being sent between each other. This will allow us to narrow the fault within your vehicle and in our previous experience it normally points to the TCM itself.
Replacing your TCM
In the early days, we recommended supplying a new genuine TCM however Mazda has increased the price over the years and it is now very expensive. The more cost effective repair is to supply and fit an exchange recondition module.
Not all modules are the same.
The exchange option is by far the best value as it will have you back on the road sooner if the module is in stock. Due to the different variants of Mazda’s, we need to match your existing module so it works with the correct software. luckily we can stock a variety or modules that we can match to your vehicle’s VIN number.
Affected Mazda Models
Mazda3 BL Neo 2.0L Petrol Sedan/Hatch 2008-2013
Mazda3 BL Maxx 2.0L Petrol Sedan/Hatch 2008-2013
Mazda3 BL SP20 2.0L Petrol Sedan/Hatch 2008-2013
Mazda3 BL SP25 2.5L Petrol Sedan/Hatch 2008-2013
Affected Mazda Transmission
5-speed Ford FNR5/Mazda FS5A-EL automatic