September marked the largest price decline for used vehicles all year, following seasonal trends most in the industry expect when the weather starts to cool.

According to Black Book data, the average price of a used vehicle for model years 2009-2013 saw the largest monthly depreciation of 2014, falling by 1.7 percent last month.

Interestingly, August saw stronger-than-normal retention, according to Black Book, with only a 1.3 percent drop, but September picked up the typical seasonal fall pattern of growing price losses at auction.

Domestic cars saw the biggest price declines in the lanes last month, with rates dropping by 3.4 percent.

Import cars fell closer to the overall average, seeing a 1.8-percent decline.

Trucks continued to see stronger price retention last month: domestic trucks fell by 1.2 percent; and import trucks fell by 1.5 percent.

Taking a look at segment movement last month, full-size passenger vans were once again ahead of the pack — for the third month in a row.

This segment actually saw growth of 0.6 percent last month.

Full-size cargo vans saw the second-best retention rates with a decline of only 0.7 percent.

Then came the trucks, which have seen unusually strong price retention all year.

Compact pickups saw a 0.9-percent month-over-month depreciation rate in September, ending the month with an average segment price of $15,692. This marks a decline of 5.7 percent from 2013 rates during the same period.

“A continuing trend over the last several months, trucks represented the vast majority of segments with the strongest performing monthly retention,” Black Book officials pointed out.

In fact, eight of the top nine segments with the strongest price retention were trucks, and 11 of the top 14 segment were trucks.

The declines were a bit larger among the car segments. The lowest depreciation rates was seen in the premium sporty cars segment, with a drop in price of 1.4 percent in September.

The average segment price at the end of September was $48,830, a decline of 12.5 percent change from year-ago levels.

On the other hand, the entry midsize cars led all segments for depreciation with a 3.2-percent month-over-month decline. The segment ended the month an average price tag of $11,601, a 13.7 percent drop from 2013 levels.

“There was very little surprise in this month’s report as it is expected that depreciation levels across the board will start to show noticeable acceleration between now and the year end,” said Ricky Beggs, editorial director at Black Book. “We will be keeping a close eye out for luxury type car segments, which are expected to show larger levels of depreciation through the remainder of the year, as well as continued falling gas prices that could impact smaller car prices.”

Last month, the luxury level cars saw a 2.9-percent decline from August but sits 16.8 percent lower in price than in September 2013. The segment ended the month with an average price of $21,111.

Black Book expects overall 2014 depreciation of 13.5 percent.