When Doing Diagnostics – Information is Key

About the Author

Jonathon "Jono" joined Wholesale Automatics in 2013 to provide a solid IT / Computers / Electronics background. Jono has been instrumental in the development of the Land Cruiser 6 Speed Automatic, Land Cruiser 5 Speed Automatic and Nissan Patrol 5 Speed Automatic Transmission Computers. Jono also leads the development of the Torque Converter Lockup kits and the Website.

When Doing Diagnostics – Information is Key

Naturally one of the most common topics for phone calls and emails from customers is about diagnostics or trying to diagnose an unknown problem. While there are many symptoms that we can interpret and provide an educated and experienced diagnosis, however sometimes we are left a little confused as the symptoms described don’t seem possible. So I wanted to provide a brief guideline of basic diagnostics that can be performed to assist us in providing an more accurate diagnosis.

Stuart Diagnostics Automatic Transmission

First rule of diagnostics is – There is no such thing as too much information. No matter how unrelated a strange happening, symptom, thump, noise or flashing light might seam, never rule it out.

One bit of information that is often overlooked is simply the details about the vehicle. We need detailed information about the vehicle as some vehicles can have 2, 3 or even 4 possible transmissions all in the same year. In order to determine which automatic transmission your vehicle has, the minimum information we need you to collect includes:

  • Make
  • Model
  • Build Month and Year
  • Engine Capacity
  • Diesel or Petrol

The next step we need you to do it to describe the problem or issue in as much detail as possible. We would prefer a little more information than ‘It does something weird when I shift to reverse’. What can really help us is to describe how to replicate the issue. For instance, “The vibration only happens when I’m on the freeway and accelerating hard to overtake another vehicle, but all other times the car drives perfectly”.

Write down your Diagnostics for your Automatic Transmission

And finally, we recommend that you write everything down so that you don’t forget any of it while you are on the phone including anything you know about the history of the vehicle and how long you have been experiencing this issue. What I mean by ‘History’ of the vehicle is:

I’ve owned the vehicle since 2010 and I have been travelling Australia since I purchased the vehicle while towing a 3T caravan and the transmission has been serviced twice in that time. I have also had the A/T Temp light come on a couple of times while heading up the Toowoomba Range. But I’ve only experienced this issue in the past 6 months.

Common Symptoms and Possible Causes

Symptom: Reverse or Drive won’t engage. Whenever I push on the accelerator, the engine revs but the car doesn’t move.

Possible Causes: The two main possible causes for this are: Loss of Fluid or Transmission Damage. Loss of fluid could simply be caused by a leak or if the transmission got too hot at some stage the fluid could come out through the breathers. First thing to do is check the fluid level for your transmission. If the fluid level is correct then most likely there is transmission damage. I recommend contacting us or your local transmission specialist to see about a physical inspection of your transmission.

Symptom: The vehicle is very sluggish to take off. The engine is also revving higher than it normally does.

Possible Causes: This generally describes what is commonly called ‘Limp Mode’ where the TCU (Transmission Control Unit) has disable gear changes and locked into a single gear. Most often it is engaged by the TCU as a safeguard because it has detected an electical error or possibly the first signs of transmission failure. Usually this will be accompanied by a flashing light on the dash. It is also possible that if the TCU has stopped working due to blown fuse or loss of power. All transmission have a default ‘No Power Mode’ which is usually the same as the ‘Limp Mode’. First check for any blown fuses.

If you can not find any blown fuses and a tow truck is not an available to you, then the vehicle can be driven in this state for the sole purpose of getting to a workshop for proper diagnostics. We would not recommending driving the vehicle on a regular basis in this condition as you have the possibility of turning a simple electrical issue into a full transmission rebuild due to being burnt out.

Symptom: The transmission neutralises in between gears.

Possible Causes: We see this one quite a bit, especially with the older vehicles. This symptom is quite often referred to as a flare. It basically means that the transmission is having troubles engaging the next gear. This can be a result of low pressure due to an incorrectly adjusted cable or excessive wear to the clutches inside the transmission. Or it could simply be the T-Bar shifter is out of alignment and occasionally makes the computer think that you have shifted into neutral.

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