Catalyzes the NAD(+)-dependent oxidation of L-carnitine to 3-dehydrocarnitine. Is specific for L-carnitine and NAD(+) as substrates. D,L-3-hydroxybutyrate, L-lactate, ethanol, L-malate and D,L-isocitrate are not substrates. Is involved in a L-carnitine degradation pathway that allows P.aeruginosa to grow on L-carnitine as the sole source of carbon and nitrogen. carnitine + NAD(+) = 3-dehydrocarnitine + H(+) + NADH Analogs of L-carnitine such as D-carnitine, glycine betaine and choline, are competitive inhibitors of L-carnitine oxidation. Optimum pH is 9-9.5 for the forward reaction (oxidation) and 7.0 for the reverse reaction (reduction). Optimum temperature is 35 degrees Celsius for the reaction in both directions. Amine and polyamine metabolism; carnitine metabolism. Homodimer. Highly induced by carnitine via the CdhR transcriptional regulator. Not induced by glycine betaine or pyruvate. Cells are incapable of growth on carnitine. Belongs to the 3-hydroxyacyl-CoA dehydrogenase family. L-carnitine dehydrogenase subfamily.