Will your car company honour it’s warranty on your modified car?

When it comes to modifying new cars there is a huge taboo and fear. Most owners who don’t want to void their warranty won’t modify their car at all. Some make modifications that can be reversed if they need to take a car in for warranty work. But what do car companies even look for when assessing a modified car with a problem? And will the honor the warranty on your modified car?

Taking your car in for a warranty repair if your car is modified can be terrifying since the decision of whether the damage was caused by the modification is often at the whim of the technician looking at the car. But there is a document in the Ford service portal that shows us at least how one manufacturer decides what caused the damage and whether they will approve a warranty repair.

The document posted on the Ford service portal and available through some public websites is called “A Guide to Identifying Failures Related to Performance Modifications” as it focuses on identifying the potential modification to the gas engines in their performance cars. Ford sells tons of cars for petrol heads, and it’s no surprise to see a document like this from the company that supplies the public with Fiesta STs and Mustangs.

The guide is a pretty interesting read because it shows that Ford is wise to your tricks. Don’t think Ford hasn’t seen your little plans before. Trying to swap stock parts back into your car will not go unnoticed.


The guide shows a simple flow-chart directing the technician to use a borescope to look inside the motor to see if damage is present and to check for related codes. The flow-chart offers a few points from that direction that lead to either a warranty repair or if they will send you packing.

Initial Checks Performed By Technicians

The guide lets technicians and service advisers inform owners that current factory approved and certified calibration or tunes are set up for maximum performance for how the cars are built. Therefore any aftermarket parts or tuning risks damage to engines and transmission.

If modifications are suspected, technicians are instructed to record specific diagnostic trouble codes (DTCs) and freeze frame data that would explain why there’s damage to the engine.

This would be stored information relating to misfires, knock, increased catalyst temperature, and lean air-fuel ratios. Looking at these specific parameters makes sense; increasing boost can cause lean fueling conditions, which can cause the engine to knock and then increase the temperature in the catalytic converter as a result of those detonations.

Covered Performance Parts

Fear not, some performance modifications are approved and covered under a separate warranty through Ford Performance. Those include products from Ford Performance, Ford Racing, and Mountune.

Technicians are instructed to check the OASIS service portal (Online Automotive Service Information System) in order to verify that the parts were installed correctly and to verify warranty information there.

So even if you have installed warranty approved parts but they were not registered correctly, you have still voided your warranty.

Commonly Found Modifications

The last section of the guide shows examples of commonly modified intake parts and spacers from brands such as Forge. It also covers modifications to the PCV (positive crankcase ventilation) system such as new catch cans or vents, explaining that such modifications can cause damage to a car’s turbo.

Since the high-pressure fuel system in Ford’s EcoBoost engines will not support much additional fuel flow on its own, tuners may add an additional fuel injection source. Ford instructs technicians to look for additional injectors in the induction system.

Don’t advertise your modifications

One of the easiest to see signs listed in the document is decals. Technicians are instructed to look for stickers or badges that name an aftermarket parts company. So what you need to do is build a sleeper. In addition to the stickers, they are also instructed to look for dash mounts for additional clocks.

The last section relating to EcoBoost engines covers common turbo modifications such as blow-off valves, wastegates, and downpipes. These modifications can get you more power (and sweet, sweet turbo noises), but they cause compressor surge or over-speed the turbo. Technicians are instructed to look for them if the engine’s turbocharger has failed.

It is always going to be risky business modifying a brand new car, so if you are planning a huge build I would just rip the warranty up as you leave the showroom.


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