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1999 Chevrolet Tahoe:
Security Light On Dash Stays On

Alex Steele
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seen in Truck Trend



I have a '99 Chevy Tahoe with a 5.7L Vortec engine. After I start the engine the security light on the dashboard will go on and stay on. I'm able to start the engine sometimes, with difficulty.


The security light is part of the Passlock system and is not working properly. I checked the fuses and used another key but neither helped.




Passlock is a second generation General Motors' theft deterrent system. With the use of a Passlock sensor (mounted in the steering column) the Passlock system can determine improper ignition key and lock cylinder operation by monitoring magnetic fields emitted by the lock cylinder assembly. Once improper operation is confirmed, engine startup is disabled.


The Passlock system eliminated the resistor chip mounted in the ignition key used by the previous Passkey system, including the headaches and expense that went along with it.


Passlock is a subsystem of the vehicle's Powertrain Control Module. The Passlock sensor sends a signal to the Passlock control module. The Passlock module reads this signal and sends the appropriate information to the Powertrain Control Module. If the ignition key and lock cylinder operates normally the engine will start as usual. If it was operated improperly the Powertrain Control Module will be directed to disable fuel injector operation, prevent engine startup, and there will be a diagnostic trouble code set in the Passlock Control Module's memory.


I just wanted to give you an understanding of system operation. It's gonna require the correct scan tool for proper diagnosis. Weak links are the circuits to and from the Passlock Sensor in the steering column. It's a very sensitive signal and can be easily affected by shoddy electrical connections.


If a scan tool displays diagnostic trouble code B2960 (Passlock sensor voltage out of range), the next step would be a resistance check and a complete inspection of connections and wiring involving the sensor. Pay the diagnostic time at a heads-up auto repair shop.


Related Topics:  

Chevrolet | Locks and Keys | Alarm System
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01 Jan 2011, 18:47
This looks like the same issue on my 1999 Tahoe. How can this be bypassed to see if this is the issue or not?

02 Jan 2011, 10:08
It's not that simple, or it wouldn't be much of a theft deterrent system.

You should check for system diagnostic trouble codes, and begin the appropriate testing as per the service manual from that point.
25 Jan 2011, 07:19
turn key to start position for 10 minutes and it will reset passlock

Or, once you're tired of being stranded for 15 min every 6 weeks or so, try the following:

Here's the "fix" I just did for my 99 tahoe. Took the cover off the steering column, unplugged the sensor from the cylinder *while* the car was running. it's a 3 wire plug red w/ white, orange w/black and yellow. From then on, the car will always start and ignore the sensor. The only negative is the security light stays on. But, I plan to just remove the bulb. Replacing the BCM only postpones it from happening again. Check out the following links. Good luck.

http://general-motors.pissedconsumer.com/gm-passlock-ii-system-has-major-in herent-design-flaws-20080502119601.html

Read more: http://wiki.answers.com/Q/1999_Chevy_Tahoe_with_passlock_problem#ixzz1C3K17 5tW
17 Oct 2011, 08:37
My girl friends 2004 grand am was doing the same thing and what i did was solder a 22k resistor between the black and yellow wires at the PCM and fixed the security system for good never have to worry about the security system again for more info google 2004 Pontiac grand am Passlock problems. car runs great
18 Jul 2012, 11:18
Yep unhooked that connector, security light stays on and truck starts!! Thank You!
02 Sep 2013, 00:27
Same prob here still no start. Scanned by auto zone said securiry issue. Background:Column shifter was broke we put pulled it replaced shifter put column back in. Guy snapped it cuz it wouldnt start often. Checked fuel reg, pressure,all ok. Scannedby auto zone, security code. Wont run at all cuts off immediatly. Did run w/ direct ether and gas.
Security light does not flash. Tried resettng passlock not doing anything the light stays on..
Ideas? That wont cost alot cuz its not our truck we helping friend.
04 Sep 2013, 14:54
These theft deterrent systems can be tricky. And often can only be diagnosed and repaired at the dealership with authorized scanning equipment and security clearance.

Usually worth the diagnostic fee. A lot of independent shops also have to bring vehicles to the dealership in this situation.
29 Sep 2013, 11:47
I have a 02 tahoe that wont start anymore.I was told it was the security system.When i turn it to start all the lights come on but the car dont start.I dont click over or nothing.You can hear the fuel pump and relay come on thats all.When the door is open the security light come on but goes off when door closes.How can i disable the security system or is it someother way to bypass it
16 Oct 2013, 12:31
Any issues with a theft deterrent system should be diagnosed at a Chevy service department. Only the Chevy technicians have the equipment to diagnoses and re-activate the system.

No, you can't bypass.
11 Jul 2014, 16:23
Search NewRockies Pro Module Bypass, just installed one on my 1999 GMC PassLock and it has started up for me everytime.
Manny Gill
22 Jul 2014, 22:18
is it worth it just to turn off the alarm system in the vehicle? I have the same problem, Once or twice a week the vehicle does crank over but doesn't start. It takes a while for it to start... i was told there maybe a wiring problem but the security light stays on sometimes. i think it may the security system disengaging something to do with the fuel going to the cylinders. Please Help ... :(
15 Oct 2014, 18:43
Your car should be scanned at the dealership because there scanner is more complex and can get by security clearances. The scanner can tell the technician trouble codes with the security system and help diagnosis sensors with the system. It may be worth the diagnostic fee to fix the problem.
15 Apr 2015, 20:06
i have a 99 chevy Tahoe does not have chip in the key. just replaced passlock on the colume and when I start it it runs for 5 secs then dies.....
16 Apr 2015, 09:57
RE: Jake, Go over your work to make sure everything is installed properly. It is advisable to bring your truck to the dealer because they have the scanner that can do more than the average repair shop scanner. Their scanner can analyze the system and locate issues that can cause this problem. Sometimes when a lock cylinder is replaced for the passlock system there is relearning process to be followed to ensure the passlock system will operate properly.


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