A class action filed in the Federal Court could affect up to 250,000 Toyota drivers nationwide, including owners of Australia's top-selling car — the Hilux.

Key points: Top-selling Toyota models are involved in class action after owners and mechanics report problems with a filter

Top-selling Toyota models are involved in class action after owners and mechanics report problems with a filter Some report fuel efficiency problems are costing $70 a week

Some report fuel efficiency problems are costing $70 a week Toyota launched a customer service campaign, but not a recall

Lawyers alleged Toyota Australia had been installing faulty Diesel Particulate Filters (DPFs) in its Hilux, Fortuner and Prado diesel cars sold nationwide from October 2015 to July 2019.

Bannister Law and Gilbert and Tobin lawyers allege the faulty filters cause foul smoke to spew from exhausts, dramatically decrease fuel efficiency and increase wear and tear on engines.

"We believe consumers are entitled to compensation for the defect we allege is in the vehicles," Charles Bannister from Bannister Law told the ABC.

"The issue is that [in] the past few years, the operation of these vehicles has cost many people time off work in returning the vehicle to the dealership [to be fixed], and the excess fuel consumption has hit their hip pocket.

"People return to have the problem fixed. It's not fixed, its fuel consumption is poor and they return again."

The case will claim drivers have suffered a "reduction in value" of their vehicles.

What's happening with the filter?

Frustrated Toyota owners began calling Andrew Leimroth's specialist diesel repair garage in 2017.

Since then, he has been inundated with complaints.

As well as toxic exhaust and fuel efficiency problems, Hilux, Fortuner, and Prado drivers were complaining about sudden power loss.

Mr Leimroth said the problems appeared to start with the DPF installed in 2.8-litre models.

"It's really inundating calls that we get all the time," he told the ABC at his garage in Berrima in New South Wales.

The DPF is meant to trap and burn soot from diesel, but customers are claiming it is getting blocked, creating more wear and tear on the engine and emitting fumes from the exhaust.

Customers claim the diesel particulate filters in some Toyotas are getting blocked. ( ABC News )

From what he had seen, Mr Leimroth said he suspected the "burn cycle" was not working correctly.

"They end up with raw diesel coming out the tailpipe with steam, and a mixture of sulphuric acid and that's of course very polluting, very hard on the eyes," he said.

Berrima Diesel's Facebook page was bombarded with hundreds of similar complaints.

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"The story they're telling us is they've had numerous attempts by the dealer to rectify the problem and now they're exercising their consumer rights to get further advice," Mr Leimroth said.

"It's a difficult one because it's a manufacturer's issue and it's all under warranty and we certainly only advise them to go back to the manufacturer and give them hell.

"Give them a hard time and pressure them because, by law, they have to fix it.

"It's obviously not an acceptable fault to have your car running around pouring out white smoke."

Couple stranded on drive to Uluru 'never got there'

Max Bancroft is ready to give Toyota a hard time and has joined the class action.

Mr Bancroft and his wife Wilma were one week into a road trip to Central Australia last year when their Toyota Prado's DPF light came on.

Max Bancroft and his wife were out of pocket after their Toyota Prado's diesel particulate filter developed a problem on a trip to Central Australia. ( ABC News: Brendan Esposito )

"Normally that light will extinguish as the filter burns itself off — that didn't happen," he said.

"Some more lights came on and we read the book that comes with the car and it said you need to get the car looked at, don't drive it. So we stopped at the first available opportunity."

They had to get their car towed nearly 300 kilometres to Alice Springs where the couple waited four days to get the car fixed by the local Toyota dealer.

Mr Bancroft said the car was OK, but the experience ruined their trip of a lifetime.

"We were booked to be at Uluru on the Monday night and we never got there," he said.

He said he was out of pocket for accommodation and he was not satisfied with Toyota's handling of the issue.

"To travel all that way and basically get within a couple of hours of the place and then not get to see it, it was very, very disappointing," he said.

The car was serviced a few months after they returned home to Sydney.

Mr Bancroft said the dealer blamed the software parameters and the engine control unit for the issue rather than the filter itself.

Max Bancroft had to have his Toyota Prado Diesel towed nearly 300km after it broke down on a trip to Alice Springs. ( ABC News: Brendan Esposito )

Hilux owner says fuel efficiency problem costing $70 per week

Mark Wolfe also signed up to the Toyota class action.

Is my Toyota affected? That all depends on its model and when it was made. According to the Toyota customer service campaign, your car has the potential to be affected, if: It is a Hilux, Prado and Fortuner model

It is a Hilux, Prado and Fortuner model Sold between June 2015 and July 26, 2019

Just a few weeks after he purchased his brand new 2017 Toyota Hilux Diesel, he noticed the poor fuel efficiency.

He estimated the car was operating at about 60 per cent fuel efficiency and that was costing him up to $70 more each week to fill the tank.

The Brisbane-based electrician said he had taken his car back to the dealer at least six times to address the faulty filter issue without success.

"Every time I have taken it in there to have a look at the actual filter to see if there's an issue with it... they always come back and say the DPF is clean," he said.

Mr Bannister said his firm had been inundated with drivers saying they had been experiencing problems.

"We've been overwhelmed by the number of consumers with completely consistent issues in relation to the operation of the vehicle, and we believe that it's a widespread problem," Mr Bannister said.

"We believe that the vehicle should be free from defects and that the representations regarding the fuel consumption of the vehicles were incorrect.

"The appropriate remedy is a class action representing all affected vehicle owners."

As angry drivers continued to vent on Berrima Diesel's Facebook page, Toyota sent Mr Leimroth a letter.

Mr Leimroth with black soot from the exhaust tailpipe of a Toyota Hilux. ( ABC News: Brendan Esposito )

It warned him that the posts on his page were "false, misleading, inflammatory and defamatory" and ordered he take them down or face legal action.

Now, the tables have turned and Toyota Australia is itself facing a legal fight, with the class action seeking compensation for drivers.

In October, the car maker launched a Customer Service Campaign offering to clean, replace, or retro-fit a switch for Hilux, Fortuna and Prado vehicles sold between June 2015 and June 2018.

All customers with potentially affected vehicles were asked to contact their Toyota dealer for testing and repair free of charge.

Company offers customer service campaign rather than recall

But the company stopped short of a full recall.

When talk of a potential class action emerged at the end of last year, Toyota Australia told the ABC it was "aware" of the DPF issues.

At the time, Toyota said it was working with customers to fix the issue.

"Toyota dealers will reprogram the engine control module, ensure the DPF has been regenerated and conduct a smoke test," it said in a statement.

"If the smoke test is negative, the DPF will be replaced. All inspection work and replacement, if required, will be completed free of charge to the customer.

"Any Toyota customers who are concerned about the DPF in their HiLux, Fortuner or Prado should contact the Guest Experience Centre on 1800 869 682 (Monday-Friday 8.30am - 5.30pm AEST) or their closest/preferred Toyota dealer."

On Thursday, Toyota Australia told the ABC it was unable to comment on the case "as this matter is before the courts".