GM Passlock

Maintenance/Repairs
1

2007 Chevy Silverado Classic 1500 LT 5.3, 4L60, 4x4, not Z71, 3006k miles. There is a lot of conflicting information in the net about this. I think I have separated the pepper from the fly specs for the most part, but one thing I am curious about is why the security light comes on steady sometimes. It does not stop the truck from starting or running. But I can’t find a reasonable explanation on why it sometimes stays on. The owners manual only says that if it is blinking, the security system has been triggered. Nothing in Haynes and I don’t own a service manual. Also I haven’t found a reasonable answer on the silverado/serra forum. I am not asking how to bypass the system BTW.

A little background, bought the truck in 2017 from the second owner. He is an older guy who had is for most or its previous life. He had all the maintenance records but it also had a hard life, but it has been very reliable. But a couple of years ago, the key would not turn in the ignition. I had to replace the lock cylinder, but because the key would not turn out of off, I had to take drastic action. To remove the cylinder, you have to turn it to the run position, poke a small screwdriver into a hole to depress a pin so it can come out. I had to drill a hole in the housing to remove the cylinder.

About a year later, the security light started coming on steady, not all the time but frequently. About six months later, it failed to start one night, but a half hour later, it started right up and the security light did not come on again for a few months. Then the cycle repeated over and over few months eventually resulting in a not start for a half hour. Again no light for a few months, but when the cycle started again, I learned how to do the system reset/relearn. As soon as I did the first one, the cycle repeats in weeks instead of months, so every couple of weeks, I have to do the relearn. When it comes on, it will stay on when the truck is running and after a couple of cycles, if I don’t do a relearn, it will start flashing and won’t start.

Right now, I believe that I will need another lock cylinder to fix this, but I will get a GM lock cylinder this time and not a cheap aftermarket. Last time, I needed the new one, I needed it right away so I got what was available. Now I do have the luxury of having the time to order a good one.

I’d just like to know why the solid light and what is it trying to tell me.

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Tester

3

You may need to replace the actual housing and do another relearn

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Normally, on steady indicates the system has detected a fault and that results in a no-start condition. The fact yours still starts and runs with the lamp on steady is strange. I would do a relearn first, if you haven’t already. If it continues to be lit up but is not impeding use of the vehicle…well, I might tend to ignore it and risk getting stuck somewhere but not everyone has the same risk tolerance :smile:

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@TwinTurbo, On steady does not interfere with starting. When it detects a fault, the light flashes and then it wont start. It will crank but the flashing security light means that the fuel pump will not be activated so it won’t start.

@db4690 , you may be right. I did drill a 1/4” hole very close to the module in the housing. But I didn’t have any issues with the Passlock for a year though. I did use a cheap aftermarket lock cylinder though because I didn’t have time to get a GM module. Inside the lock cylinder there is a hall effect sensor that detects when all the tumblers are correct in the run position. As they age, they are known for taking longer to detect the tumbler positions so if you go through run to start too fast, it will trip the passlock.

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On solid means a fault has been detected during the self-test portion of the start up. Flashing happens when the system detects a entry attempt without the proper key being detected.

What the Light Means

A blinking light typically means the system is actively preventing the car from starting and may require a 10-minute reset procedure.

A solid light usually indicates a fault in the system, often a problem with the Passlock sensor or the ignition lock cylinder itself.

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Thank you. I have seen the definition of the flashing light in several sources, but no definition of what a solid light indicates. I think I will start with a new lock cylinder and if I get a solid light again, then I will do the housing, but that looks like it isn’t fun to do.