This paper presents a modeling procedure and diagnostic algorithm for fixture related faults in panel assembly. From geometric information about the panel and fixture, a fixture fault model can be constructed off-line. Combining the fault model with inline panel dimensional measurements, the algorithm is capable of detecting and classifying multiple fixture faults. The algorithm, which relies heavily on the fault model, is based on least squares estimation. Consequently, the test is of relatively simple form and is easily implemented and analyzed. Experimental results of applying the algorithm to an autobody assemble process are provided.