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Hello, as simple a thing as you would think an ignition lock cylinder is, you would not think they would be too hard to diagnose or fix. Sorry to say these new one are actually pretty complex. There is the possibility that the shift linkage is out of adjustment or has something in it someplace that is loose. There is a possibility that the stop lamp switch on the brake pedal is out of adjustment. Also possible that the ignition lock solenoid under the console or its linkage is not adjusted correctly or has something loose. There is even yet the possibility that the lock cylinder itself needs to be replaced because of bad tumblers in it. It only takes one of those little brass inserts to get out of alignment to cause a problem. Then there are also a couple of factory bulletins that could be the cause. I am going to send you the bulletins from the GM Hummer service manual and let you take a look at them as a starting place. If one of them is the problem and it gets cured for you, great. If not, let me know and we will go through some diagnostics and checks on the other parts of the system before we start replacing any parts. The whole idea being, to try to save you as much money as we can. Take a look at the bulletins posted below and let me know. Thanks
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
If you encounter a situation where the ignition key cannot be removed from the lock cylinder, the most probable cause is a broken wire or harness disconnect at the automatic transmission shift lock control solenoid located under the shift plate on the console. Simply correct the open circuit condition and provide enough slack in the harness to allow for full travel of the shift lever without placing any tension on the harness.
Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.
(03, 04 HUMMER H2)
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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.
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.)
Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
(1999 - 2005 Chevrolet All Full Size Trucks and Utilities) and (1999 - 2005 GMC All Full Size Trucks and Utilities) and (2003 - 2005 H2 Hummer)