<p>If the key turns in the door but not the ignition I would replace the ignition lock cylinder. </p><p> </p><p>#PIT3382: Service VME - 99-05 Cadillac/Chevrolet/GMC/Hummer All Full Size Trucks and Utilities Ignition Key Cannot Be Rotated in the Steering Column Lock Cylinder - kw inoperative stuck - (Jan 17, 2005) </p><p><img src="http://gsi.xw.gm.com/image_en_us/gif/000/999/999/999999995.gif" alt="" width="90" height="90" align="right" /> <table border="0"><tbody><tr><td width="100" valign="top"><strong>Subject:</strong></td><td valign="top"><strong>99-05 Cadillac/Chevrolet/GMC/Hummer All Full Size Trucks and Utilities Ignition Key Cannot Be Rotated in Steering Column Lock Cylinder </strong></td></tr></tbody></table></p><p><table border="0"><tbody><tr><td width="100" valign="top"><strong>Models:</strong></td><td valign="top"><strong>.</strong></td></tr></tbody></table></p><p> </p><hr /><p>The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.</p><p><a name="ss1-1582590" title="ss1-1582590"></a><a href="http://gsi.xw.gm.com/si/showDoc.do?docSyskey=1582590&from=sm#ss1-1582590"><h3>Service VME</h3></a></p><p>Some ignition key cylinders may not be able to rotate in the ignition cylinder housing because of a dirt build-up inside of the key tumbler housing. Very often a "Lint" type of build-up (over time) is found in the tumbler housing restricting the movement of the tumblers and not allowing the side bar on the outside of the housing to fully retract when the key is inserted into the lock cylinder. Before replacing the ignition cylinder and housing assembly, the tumblers may be able to be freed up temporarily in order for the key to rotate so the lock cylinder can be removed for cleaning. Using compressed air (60 PSI max.), or an aerosol can of Brake-Kleen, place the nozzle of the air gun or nozzle of the aerosol can at the entrance of the key cylinder. Give it a couple of short blasts of air or cleaner into the key housing. Insert the key and try to rotate the lock cylinder. This procedure may have to be repeated a couple of times to dislodge the debris. If successful, remove the key cylinder and disassemble noting the position of the key code tumblers in their respective slots for reassembly purposes. Clean the key cylinder with Brake Kleen or equivalent solvent and reassemble the key cylinder. Lightly oil the inside of the key cylinder with multipurpose lubricant. However, some key cylinders and housing assemblies may need to be replaced because of casting flash in the tumbler areas and interferes with tumbler activity and cannot be dislodged using the cleaning method. ( Note: Check for a slightly bent key as this has been known to bind the ignition lock cylinder also.) </p>