Jim Grant's Tech Tips

'93 Buick LeSabre, Computer Lock-out

Q: I bought my father a ‘93 Buick LeSabre with 97k for $2000 from a co-worker. It worked beautifully until one morning it wouldn't start. Our mechanic can start the car from under the hood so he doesn't think it is the starter. When he turns the key the security light flashes. He thinks the car has locked itself down and will not respond to either of our keys. It has been in the shop for 4 days and we are no closer to getting the problem solved.

A: If you take a look at the ignition key to the vehicle you will see a small black chip with a small piece of metal on each side. This chip has an electrical value that is used by the vehicle’s security system to allow the vehicle to be started. There are 2 common problems with the system used in your father’s vehicle. The chip in the key goes bad so no signal is sent to the security system or the tumbler and housing that the key goes into is worn and will not allow the signal/code from the chip to get sent to the security system. The fix? Replace one or the other or both. But there is a catch. The security system has to receive the right signal/code and not just any signal/code. It has to be the right one for your vehicle or it will never start. How do you prove this is the problem? Take an ohm meter to the metal on each side of the chip on the key and record the readings/values. Then under the dash of the vehicle there will be a small 2 wire connectors that come from the key and tumbler housing. Unplug this connector and check the values and compare it to the reading recorded from the key chip. This has to be performed with the key installed. Then turn the key in the housing and monitor the values. If there is a sudden change just for a moment the key housing/tumbler is bad and has to be replaced. Why? Because the security system thinks someone is messing with the vehicle and will not allow it to start. If the key chip is bad you’ll have to have the vehicle towed to your nearest GM dealer. They have this tool/computer that goes in place of the key and ids the security system code. This will allow them to make up a new key to replace the one with the failed chip. The local hardware store just can’t help with this one.