My key broke off in the ignition?

What part actually broke off? There is a recall for this issue if it was the housing that broke off. You would need to call GM to see if it applies. Here is what the recall says about the housing breaking off. Let us know if this is the issue.

Collision

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2009 Chevrolet Impala

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V6-3.5L

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Recall - Unintended Ignition Key Rotation

Vehicle Starting and Charging Starting System Key Technical Service Bulletins Recall - Unintended Ignition Key Rotation

RECALL - UNINTENDED IGNITION KEY ROTATION

# 14299D: Product Safety - Unintended Ignition Key Rotation - (Nov 24, 2014)

Subject: 14299D - Unintended Ignition Key Rotation Models: 2005-2009 Buick Allure (Canada) 2005-2009 Buick LaCrosse 2006-2011 Buick Lucerne 2000-2005 Cadillac DeVille 2006-2011 Cadillac DTS 2006-2007 Chevrolet Monte Carlo 2006-2013 Chevrolet Impala 2014 Chevrolet Impala Limited (U.S. Fleet Only)

In the Parts Information section, the quantity per vehicle repair approximation for one tube of Loctite Adhesive 426(TM) has been changed from 125 to 100 vehicles. In the Service Procedure section, the first bullet in the note at the beginning of procedure has been modified to clarify that either repair is acceptable and may be performed at the dealer's discretion. New photographs and text have also been added. Additionally, a copy of the customer notification letter is now included. Please discard all copies of 14299C.

It is a violation of Federal law for a dealer to deliver a new motor vehicle or any new or used item of motor vehicle equipment (including a tire) covered by this notification under a sale or lease until the defect or noncompliance is remedied.

Vehicles involved in this recall were placed on stop delivery June 20, 2014. Once the service procedure contained in this bulletin has been performed on the vehicle, the vehicle is released from stop delivery and the vehicle can be delivered to the customer.

All involved vehicles that are in dealer inventory must be held and not delivered to customers, dealer traded, or used for demonstration purposes until the repair contained in this bulletin has been performed on the vehicle.

Condition

General Motors has decided that a defect which relates to motor vehicle safety exists in all 2005-2009 model year (MY) Buick Allure (Canada), 2005-2009 MY Buick LaCrosse, 2006-2011 MY Buick Lucerne, 2000-2005 MY Cadillac DeVille, 2006-2011 MY Cadillac DTS, 2006-2007 MY Chevrolet Monte Carlo, 2006-2013 MY Chevrolet Impala and 2014 MY Chevrolet Impala Limited (U.S. Fleet Only) vehicles. If the key ring is carrying added weight and the vehicle goes off road or experiences some other jarring event, it may unintentionally move the key away from the "run" position. If this occurs, engine power, power steering and power braking will be affected, increasing the risk of a crash. If the ignition switch is not in the run position, the air bags may not deploy if the vehicle is involved in a crash, increasing the risk of injury or fatality.

Correction

Dealers are to install two 16mm key rings and an insert in the key slot or a cover over the key head on all ignition keys.

Vehicles Involved

All involved vehicles are identified by Vehicle Identification Number on the Investigate Vehicle History screen in GM Global Warranty Management system. Dealership service personnel should always check this site to confirm vehicle involvement prior to beginning any required inspections and/or repairs. It is important to routinely use this tool to verify eligibility because not all similar vehicles may be involved regardless of description or option content.

For dealers with involved vehicles, a listing with involved vehicles containing the complete vehicle identification number, customer name, and address information has been prepared and will be provided to U.S. And Canadian dealers through the GM GlobalConnect Recall Reports, or sent directly to export dealers. Dealers will not have a report available if they have no involved vehicles currently assigned.

The listing may contain customer names and addresses obtained from Motor Vehicle Registration Records. The use of such motor vehicle registration data for any purpose other than follow-up necessary to complete this recall is a violation of law in several states/provinces/countries. Accordingly, you are urged to limit the use of this report to the follow-up necessary to complete this recall.

Contact a locksmith, they have tools that can extract the broken piece and then cut you pair of new keys and program them for less than a dealer. If you want to make a key extractor you can try to fish out the remainder. They are nothing special. The ones I use the most are nothing but lightly modified jig saw blades. They have one side of the teeth ground down smooth and in use you slide them net to the broken key and pull while twisting the extractor lightly. Like this: https://www.youtube.com/watch?v=63tQH1DIqIw

As far as swapping your transponder into a new key, the new cylinders do not come with keys for the most part, they come as a bare cylinder that you match to your key. The ones that do come with keys have the head molded to the key. If you can get the broken piece out you may have a cheaper option though. Take it and have a new non transponder key cut. Verify that the new key will work in the ignition and locks, take the head of your old key and hold it tight to the head of the new key and put a couple wraps of tape around it. It should work as a key to let you drive it to the locksmith to have a couple new transponder keys made. That would save the house call charge at least. Now for the hard part, adding the new keys.
With a previously learned master key (the taped one), turn ON the ignition, do not start the engine. Now turn it off and within 10 seconds insert one of the new cut keys and turn that key on. The vehicle has now learned the new key. Turn it off and try to start the car, if it learned the key it will start and run with no security problems. Repeat for the second key.
Now what this doesn't do that the other method using a programmer would is delete any old keys so that only the new keys start the car.

If you don't need the car immediately you can order new blanks online for much less than either other option, from places like carandtruckremotes.com. Now that you have the blanks any key place can cut them and you know how to program them.

It's possible that the key isn't triggering the key in ignition switch. If you put the key in and open the door do you hear the warning for key left in? If not it may be the switch. I've used the method you are using multiple times so I'm thinking something inside the cylinder isn't right. Another item might be the tape you used. If it has any metallic material it may block the signal.

Not really, using the correct key should turn off the immobilizer and let it start.