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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.


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Chevrolet | Locks and Keys | Alarm System
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03 Feb 2016, 06:19
RE: Frank, The security light should go on for a few seconds then go out. Start the truck; if the operation of the engine is working properly the light should go out after a few seconds. If it remains on or flashes and the engine stalls or won't start then diagnostics with a scan tool is needed to check for trouble codes. A simple thing to do is to just try another key and see if there is any change in the light status.

This is a very sensitive system. Loose connections, bad key, broken wires can all cause problems and make the light go on and store trouble codes. A good certified mechanic with knowledge of this security system should do the diagnostics and repairs.
02 Feb 2016, 23:58
I have a 1998 Chevy Tahoe that my security light stays on when I crank it, it only stays on for like 5 seconds and turns off need help
25 Jan 2016, 19:54
RE: Paredes R. Ocampo, There is a service bulletin on this that may explain the security condition. A scan tool is needed and you need to scan the body computer for a code DTC B2960 (Security System Sensor Data Incorrect but Valid).

You can try something very simple and just try another (spare) key and see if the problem goes away. If this suggestion does not work then proceed to procedure below.

With the Doors closed, place the key in the lock cylinder and turn to the Run position. Observe the Security indicator lamp. If the lamp is On and does not go Off however, the engine starts. This indicates that the system detected a fault when the engine was running.
When the lamp flashes On and Off. This indicates a problem has been detected by the Passlock system and the engine may not start this key cycle, a current condition.

Most common conditions related to this can be poor wire connection in the circuit, corrosion between connectors in the Passlock system circuit, broken wire inside the insulation, poor crimps on wire connectors and a wire may have rubbed through and is intermittently touching metal and is grounding the wire. Sometimes the problem can be found in a connector numbered C201. It is the connector for the steering column to the IP wiring harness on the left side of the column about half way down. It is a 48-way connector with a center retaining screw. Caution should be used in this area because a possible discharge of the Air Bag system (SRS) could result.

This is a complicated system and a scan tool and a VOLT\OHM meter and a wire schematic is needed to diagnosis this problem. This may be a job for your local Chevy dealer.
paredes r. ocampo
25 Jan 2016, 18:38
Hi guys I have a 1999 GMC k2500 6.5 turbo diesel. After filling up from the gas station my truck won't start. It just keeps on cranking but won't lite up. I notice the security light on the dash flashing after several attempts and wait. I disconnect the battery just to get a reset, no luck till finally I run out of options. I call a tow truck to tow to my driveway. So after several hours I try my luck and the truck started. No security light flashing but after a while maybe 10 minutes of idling light came back and stays on no flashing. I turn off ignition, restart and it starts but security light still stays on steady. what could be causing this? scared to drive the truck I might get stuck somewhere isolated any idea? help..
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.
15 Apr 2015, 20:06
I have a '99 Chevy Tahoe. It does not have a chip in the key. I just replaced the passlock on the column and when I start it, it runs for 5 seconds, then dies...
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.
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 ... :(
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 every time.
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.
29 Sep 2013, 11:47
I have an '02 Tahoe that won't start anymore. I was told it was the security system. When I turn it to start all the lights come on but the car doesn't start. Ir doesn't click over or anything. You can hear the fuel pump and relay come on but that's all. When the door is open the security light comes on, but goes off when the door closes. How can I disable the security system or is there some other way to bypass it?
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.
02 Sep 2013, 00:27
Same prob here still no start. Scanned by auto zone said security issue. Background: Column shifter was broke we put pulled it and replaced shifter, and put the column back in. Guy snapped it cuz it wouldnt start often. Checked fuel regulator, pressure, all ok. Scanned by auto zone, security code. Wont run at all, cuts off immediately. Did run with direct either and gas.
Security light does not flash. Tried resetting passlock, but not doing anything, the light stays on.
Ideas? That won't cost a lot cuz its not our truck. We're helping friend.
18 Jul 2012, 11:18
Yep unhooked that connector, security light stays on and truck starts! Thank You!
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
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
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.
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?



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