Citroen C4 Aircross Flex Pipe

A loud blow or tick that gets worse as you lift off the throttle, exhaust smell inside the car at idle, vibration into the floorpan, and visible fraying of the braid on a hoist. On the C2 and the Xsara HDi the flex is reliably the first exhaust section to fail, so on those cars it is worth checking first rather than last when chasing a new noise.

Generic flex sections run R190 to R850 through our network, and we carry Citroen-specific units alongside them. Fitting is one to two hours of cut-and-weld work at any competent exhaust shop. While the section is off, ask them to check the engine mounts — soft mounts are what tore the last one, and fitting a new flex to a car with collapsed mounts simply starts the clock again.

Welding a torn flex is a false economy. The braid and the bellows are thin, and a weld bead creates a hard spot immediately adjacent to a section designed to move — so the repair fails at the weld boundary, usually within weeks. The correct job is to cut the old section out entirely and weld a new flex in, which is quick, inexpensive and lasts. Any shop offering to patch it is saving you money this month and costing you money next month.

R190 at the budget end to around R850 for a premium stainless unit, with Citroen-specific parts available through our network. In practice most flex pipes get replaced as part of a front-pipe repair rather than on their own, because the section has to come off the car either way. Ask for a fitted quote rather than a parts price — the labour is the bigger half.

A failed or seized flex is the leading cause, because with nothing absorbing engine movement the vibration goes straight into the system and then into the body. The two other candidates are collapsed engine or gearbox mounts, which let the engine move far more than the flex was designed to accommodate, and a loose heat shield, which buzzes rather than shakes. All three are a two-minute inspection on a ramp, so get it looked at rather than guessed.