The complaint usually arrives as a question about the next job rather than the current one: the section has to come off, and the workshop says the subframe has to drop first. Nothing is broken. The part was made as one continuous piece, and no straight-line path exists to withdraw it past the structure around it.
Trapped is a geometry problem, not a fastening problem. The section is bolted or clamped at both ends, but even with the fasteners out it cannot move far enough along any axis to clear the tunnel, the brace or the subframe leg before it hits something else. Removal is blocked by the shape of the pipe.
It happens honestly. The car is assembled around the exhaust on the production line, and a fabricator working from a car on a lift can build a run that passes through a space that only exists when the subframe is not fitted. The pipe fits, it clears, it works. The consequence appears on the first removal.
A second route into the same problem is a repair or a modified section welded in place. Cutting out a damaged length and welding a new one in the car restores function, but if the new piece spans a point that the original was assembled across, service access has been quietly removed and nobody notices until later.
A seized slip joint feels identical from outside: the section will not come free and force gets applied where force should not go. The difference is that a seized joint will move once the corrosion or the clamp crush is dealt with. A trapped section will not move whatever is done to it, because the obstruction is the body.
With the fasteners out, try to move the section in each direction and watch where it contacts. If it swings freely but stops hard against structure within a short distance, it is trapped. If it will not move at all at either end, the joints have seized and the geometry question is not the issue yet.
Trace the joint line and mark every point where the section could split. A flange pair, a sleeve, a v-band and a clamp all count. Then draw the corridor the section would have to travel to leave the car, and mark what sits inside that corridor: the subframe, the brace, the fuel lines, the tank strap.
Measure the longest rigid length between two splits. That length is what has to pass through the corridor, so reducing it by adding a split reduces the space needed. It is a check an owner can do with a torch and a tape on ramps, and it turns a vague complaint into a defined number of splits.
Where a section is trapped, the fix is a service joint placed so that the resulting pieces can be withdrawn. The joint wants to sit where a workshop can reach it, not at the tightest point of the run, and it should seal reliably after being opened, which usually means a flange or a sleeve with a proper clamp rather than a butt weld that has to be cut.
A joint added for access is not free. It adds a leak path, weight and a place where alignment must be maintained. That is why it belongs in the original layout rather than being retrofitted after the first removal goes badly, and why a section that will be serviced often deserves a split even when the pipe would clear without one.
If the system is being made rather than repaired, say what has to be removed in service and how often. A clutch job, a starter, a gearbox mount or a tank sender all change which sections have to come out. A fabricator who knows that can place the splits accordingly, and the custom work process page covers how those requirements are captured before cutting starts.
For a part already on the car, the practical answer is usually to add one split at the point that halves the longest rigid length, then check the withdrawal path again. That is a small amount of work compared with dropping a subframe every time the section needs attention. The exhaust pipe sections range covers the sleeves and bends a split needs.
