The Bluebirds fell behind eight minutes before the break when Garath McCleary volleyed home but the visitors salvaged a point when Lex Immers nodded in midway through the second half.
Cardiff had enjoyed a decent run of form, with four wins from their previous six games, and ahead of kick-off sat just one point adrift of Sheffield Wednesday in the final play-off spot.
Although Reading reached the FA Cup quarter-finals, losing 2-0 to Crystal Palace last week, they had won only four league matches in 15 since Brian McDermott returned as manager in December.
Reading threatened first with a speculative 30-yard effort from Ola John but Cardiff goalkeeper Simon Moore, after an initial fumble, eventually gathered the ball safely.
John then released Yann Kermorgant with a precise pass through the middle only for Moore to rush from his goal-line to deny the Frenchman.
Cardiff finally got going, with left back Scott Malone drilling over a cross from the left flank but no team-mate was on hand to apply the finishing touch.
The Welsh side went even closer soon after, when a Joe Ralls centre found Craig Noone unmarked at the far post. The midfielder headed the ball powerfully but, with home keeper Ali Al-Habsi well beaten, the ball bounced up onto the bar and away to safety.
Cardiff paid dearly for the miss, with Reading going ahead in the 37th minute. John crossed from the left, Kermorgant flicked it on and substitute McCleary - on for the injured Hal Robson-Kanu - showed excellent chest control before volleying home past Moore.
John should have made it 2-0 shortly before half time when scampering through alone but he shot tamely wide.
Reading retained control after the interval but were restricted mainly to shots from long range as efforts from John and Andy Taylor drifted wide and Moore comfortably saved another attempt from John.
Cardiff improved gradually, with a Ralls free-kick flashing across the face of Al-Habsi's goal, but they were rewarded for their persistence when they drew level in the 65th minute.
Substitute Sammy Ameobi had been on the pitch only a matter of seconds when his deflected shot spun onto Al-Habsi's left-hand post and bounced back kindly for Immers to nod in from close range.
Cardiff could yet have lost when Matej Vydra volleyed instinctively towards goal but Moore pulled off a superb save to preserve their point.
Reading : Al-Habsi, Gunter, Taylor, Cooper, McShane (c), Hector, Williams, Quinn (Cox 78), John, Robson-Kanu, Kermorgant (Vydra 61).
Subs : Bond, Norwood, Obita, McCleary, Ferdinand.
Cardiff : Moore, Peltier, Connolly, Manga, Malone, Ralls, O’Keefe (Gunnarsson 65), Noone (Ameobi 65), Lawrence, Immers, Pilkington.
Subs : Wilson, Fábio, Morrison, Dikgacoi, Saadi.
Attendance : 17,407 (1,810 away fans)