Transmission malfunction - Only a limited number of gears are accessible.

[CrawlerTagz]

Greetings!
Although I conducted thorough research on this subject, I have yet to discover a definitive solution.

Today, I engaged in intense off-roading activities in the Anza Borrego Desert. The vehicle performed well despite the scorching temperatures reaching a peak of 96F. Subsequently, I had a gearbox failure. Only a limited number of gears with the letter 'F' are available.
While ascending from the desert bottom to my tent, I saw the defect. I was most likely in the third gear and the engine was generating impressive power. The inclination is characterised by a significant slope and spans a distance of about 10 kilometres.

By chance, I glanced at the dashboard and saw the malfunction. Stopped the vehicle, connected the diagnostic equipment, and performed a fault scan. No results were found. Turn off the vehicle, then resume it. There should be no issues now.

This has occurred on several occasions. On almost every occasion when I go off the paved road. However, often on the path rather than on the roadway. The issue often resolves itself with a prompt reboot.
Every day, I operate the vehicle without encountering any difficulties, whether I am driving in the city or on the highway. I am grateful that the vehicle is not immobilised in park due to the malfunction, as many others are experiencing.

The vehicle is a 2009 model truck with a 4.4-liter engine and the HSE trim. It has been driven for a total of 167,000 kilometres.
Replacement brake light bulbs
I conducted a gearbox service at about 160,000 miles, ensuring that I used the appropriate zf fluid and filled it correctly.
Replacement battery installed at 155,000 miles.
Installed a new authentic Denso alternator at 160,000 miles.

I plan to inspect the terminals of my battery and the electrical grounds tomorrow morning. Are there any other particular aspects I should consider? I came saw a graphic depicting the A-pillar sill of the Discovery 3. I believe that the concept of highlighting is a topic worth investigating.

[CrawlerTagz]

I find it implausible that the problem would be attributed to a faulty ground or wiring. This phenomenon occurs only when I am driving off-road or when the vehicle is experiencing a significant amount of weight or stress. If there were issues with the wiring or grounding, wouldn't these problems manifest themselves during my usual everyday use of the truck?

This occurrence is exclusive to instances when I am engaged in off-road driving. Typically, I adhere to the principle of driving at the slowest speed feasible while yet maintaining an adequate pace. Therefore, I do not drive aggressively in any way. However, while acknowledging that, I suppose the blame is attributed to the presence of extra weight when driving? I am completely perplexed.

Do you have any suggestions or thoughts?

I am now composing this message on my mobile device, which is experiencing a weak signal strength of just one bar. I am situated inside a tent located in a mountainous region, finding the situation rather amusing. I will address this matter in the morning while enjoying my camp coffee.

Thank you to everybody!

[CrawlerTagz]

Furthermore, every time I connect the gap tool while the engine is running at idle, it constantly displays a voltage reading of 13.5v-13.6v.

[Finestey]

I may be mistaken, but it seems like the gear box oil and filter need to be changed. Additionally, it is possible that the vehicle is due for a service.

[CrawlerTagz]

Yes, completed. In my first post, I said that I had already completed that task. Replacement of fluid and filter.

[Finestey]

Apologies for not seeing it before. I have another idea: the issue might be related to a malfunctioning wheel speed sensor. When these sensors become problematic, they can cause difficulties with the gearbox. On a positive note, the battery voltage seems to be satisfactory. 👍

[CrawlerTagz]

Excellent cognitive abilities! I will investigate that!

[Finestey]

If feasible, please provide a live reading.

[CrawlerTagz]

I am not receiving any orange light. The only components shown on the green LCD are the letter F and the digital message "transmission fault limited gears available". I have no recollection of seeing anything of an orange hue.

[Videoman]

The gearbox may display the F fault when it becomes overheated, such as during hot weather, uphill driving, or when subjected to heavy loads. Nevertheless, using this method will result in the illumination of an orange fault indicator on the dashboard, indicating the presence of a recorded problem in the system.

The issue resolves spontaneously after the gearbox has been idle and has sufficiently cooled down.

[SushySosa]

Inspect the wheel speed sensors and wheel bearings.

[CrawlerTagz]

The speed sensors are providing reliable measurements.

Perhaps it is only experiencing excessive heat. However, that does seem peculiar. Only in off-road terrain, once again. I have driven extensively on highways and in urban areas, both for long distances and small trips, and the issue has never shown itself.

[SushySosa]

Out of curiosity, are you operating in the high or low mode when doing this task?

[CrawlerTagz]

Has occurred in both high and low ranges. I believe this occurs when the engine revolutions are elevated, accompanied by the introduction of a certain kind of burden.
The vehicle may be driven at speeds ranging from 20 to 50 miles per hour in sand mode, manoeuvring through sluggish ruts or engaging in rock crawling where the engine revs fast to overcome obstacles. Recently, it has also been used for a challenging ascent on a steep and scorching road in the desert.

[SushySosa]

Did you replace the five seals between the gearbox and mechatronic when you performed the fluid and filter replacement?

[CrawlerTagz]

Furthermore, other from replacing the new fluid and filter, I also substituted this item.

[SushySosa]

There are four cylindrical seals and a rectangle seal positioned between the gearbox and mechatronic unit.

However, it is possible that the temperature is just becoming too high. Have you ever performed maintenance on the radiator by cleaning or blowing it out? With a mileage of 177,000 kilometres, it is quite likely that there is a considerable amount of debris and clutter present in the vehicle. Based on my recollection, the trans coolers of the L320 model from 2005 to 2009 are built inside the radiator.

As a minor point, we removed a radiator from an L322 vehicle that had accumulated almost 400,000 kilometres and was completely obstructed. The vehicle experienced excessive heat, resulting in the failure of the head gaskets and the rupture of the radiator. The customer was travelling at a speed of 110mph on the autobahn when it abruptly ceased functioning.