2004 Audi A4: what breaks, and at what mileage

The failures owners actually file about

Owners have reported 39 named failure modes on the 2004 Audi A4, and the three most-reported carry 33% of everything filed, which is an unusually even spread for one model year.

Fuel pump failure leads with 48 reports, about 3.0 per 1,000 vehicles and with the middle half of reports between 49k to 82,500 miles.

Other wheel or tire problem follows with 14 reports, usually reported between 4k to 35,000 miles.

Other engine problem follows with 13 reports, usually reported between 49k to 100,000 miles.

By system, the reports fall mostly into fuel (56), engine (35) and adas (16).

How bad it is when it goes

Across the named modes, 5 mention a crash, 5 a fire and 2 an injury. Those are the words owners used in their own complaints, and NHTSA does not verify them, but they are the closest thing in this data to a measure of what a failure actually did.

The average severity weight across every report on this year is 4.25, where a stalled engine or a failed airbag weighs many times more than a rattling trim panel, and a figure this high means the reports are dominated by failures with safety consequences rather than annoyances. The weighting is set out in full on the methodology page.

What the top failures cost to put right, as editorial estimates for an independent US shop rather than figures from NHTSA: fuel pump failure at $600–$2,600, other wheel or tire problem at $200–$1,500, other engine problem at $300–$4,000 and airbag warning light or occupant sensor fault at $300–$1,600. Dealer labour, a seized bolt or a part that is no longer made can push any of these past the top of its range.

22% of the reports on this year sit in the engine, transmission, drivetrain or cooling systems — the four where a repair bill is usually four figures.

How often, against how many were built

Scaled by an estimate of how many of these cars exist, the 2004 Audi A4 draws about 14 per 1,000 vehicles, which puts it in the 88th percentile of complaint rates among 2004 vehicles we can rate.

That denominator is the weakest number on the page and it is fair to say so plainly. Rate per 1,000 uses a fleet-size estimate derived from recall paperwork for this exact model year. It is a lower bound.

The working figure is 16,204 vehicles. If the true number is twice that, every rate on this page is half what it says; the ranking against other 2004 vehicles, which is what the risk score uses, is far more robust than the rate itself.

Recalls on the 2004 model year

NHTSA has issued 3 recall campaigns covering the 2004 Audi A4, affecting an estimated 18,695 vehicles. A recall is a different kind of evidence from a complaint: it is the regulator and the manufacturer agreeing that something has to be fixed, and the fix is free for as long as the car exists.

The campaigns cover air bags:frontal:passenger side:inflator module, engine and engine cooling:engine and exterior lighting:headlights. Whether the work was actually done on the car in front of you is a question only the VIN can answer, and the manufacturer or NHTSA will answer it free.

Recalls also distort complaint counts. Publicity about a campaign reminds owners that complaining is possible, so reports for a recalled component often spike after the recall rather than before it.

How 2004 compares with the other years

High risk for a 2004 — 139th riskiest of the 329 2004 vehicles we can rate. The comparison is always within the same model year, so an older car is never penalised for having had longer to break.

Across the 27 model years of this car that carry enough reports to score, 2016 comes out best at 56 and 2021 worst at 80, with 2004 itself at 68.

If the model year is negotiable, 2016, 2014, 1996 and 2011 score lower than 2004 by a margin worth acting on. Same body, same engines, different luck — usually a supplier change or a mid-cycle fix, which the complaint data can show but never explain.

Within the 1996–2004 generation specifically, 1996 is the strongest year at 62 and 2002 the weakest at 74.

What to look at before buying one

The mileages below are where the first quarter of reports for each mode had already been filed, which makes them the point at which a fault is worth looking for rather than the point at which it happens: other wheel or tire problem from about 4k, other speed control problem from about 29k, headlight failure or clouding from about 48k and other engine problem from about 49k.

On a 2004 Audi A4 with more miles than that on it, the useful question to put to a seller or a mechanic is whether other wheel or tire problem has been dealt with, and if so with what parts and at whose expense. A car that has already had the repair is in a different position from one that has not.

None of this is a diagnosis. It is a list of what other owners of the same model year reported, ordered by when they reported it, which is a good place to point an inspection and a poor place to stop.

Where these figures stop being useful

225 owner reports; fleet size estimated from this year's own recall paperwork. Every count on this page is therefore a floor: it is the number of owners who went to the trouble of filing with a federal agency, which is a small and self-selected fraction of the owners who had the fault.

Of those 225 reports, 197 carried an odometer reading, so the mileages here describe 88% of the sample rather than all of it. Owners also round: readings pile up on multiples of ten thousand, which is why this site publishes "about 90,000 miles" and not "91,438".

Named failure modes come from matching phrases in the complaint text, so a badly worded complaint can land in the wrong bucket. The effect washes out across hundreds of reports and does not wash out across five.

And nothing here predicts what one car will do. These are other people's complaints, filed years apart, on cars maintained by strangers. Read the page as a map of where this model year has previously gone wrong, then have the specific car in front of you inspected.