September saw an overall rise in average values of 0.6% (£46 to £7,436) following an increase of 2.6% (£187) in August and they are now 24.4% (£1,457) higher than 12 months ago.
Average wholesale fleet values fell by 2% or £131 to £6,550, by in September according to the latest market analysis for cars from Manheim.
The drop marks the first decrease in average values in the fleet sector since December 2008.
Although the September rise is the eighth month-on-month increase in overall values since the beginning of the year, the rate of increase seems to be slow suggesting that the market may finally be reaching a plateau.
Average values were up in the other two sectors with manufacturer stock rising by 2.8% (£360 to £13,404) and dealer part-exchanges up by 6.2% (£140 to £2,413).
Within the fleet sector, examples of notable decreases in average values include superminis, compact executive models and 4x4s which fell by 6.9% (£277 to £3,748), by 4.0% (£370 to £8,961) and by 6.3% (£771 to £11,414) respectively.
Examples of notable increases in average values include fleet-sourced small hatchbacks and medium family models which rose by 8.0% (£361 to £4,897) and by 2.2% (£128 to £6,048) respectively.
In the dealer part-exchange sector executive models increased by 16.9% (£597 to £4,117) and 4x4s increased by 13.6% (£554 to £4,632).
Meanwhile, in the manufacturer sector small hatchbacks increased by 9.2% (£771 to £9,170) and MPVs were up by 2.9% (£381 to £13,452).
Mike Pilkington, managing director Manheim Auctions and remarketing, said: “The first recorded fall in average values in the fleet sector this year and the modest increase in overall values suggests that the market is inevitably beginning to level off after unprecedented growth this year.
“Conversion rates also fell in September; however they remain significantly higher than September 2008 levels. Although we do not foresee any major fall in overall values because stock levels are reducing and buyer interest remains high, we are cautioning vendors to adopt realistic pricing strategies to ensure that vehicles are sold in the weakening market.”