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2005 Silverado 1500 Security Light/no start

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I recently bought a 2005 Silverado from a co worker and it’s making me pull my hair out. It’s a 2005 1500 with 217k on the clock and the security light has been coming on. Sometimes it comes on when driving and at the worst, it will turn on/flash when I go to start it, forcing me to do the relearn procedure (try to start, leave key on position, wait 10 min x 3). It has done three times in the last three weeks and it’s driving me crazy. 


I called the dealership and they confirmed that it is NOT a chipped key by VIN. The original set of keys had been stolen so I have been using the spares he provided me and sometimes I have to jiggle them in the ignition for it to turn over. I have been researching it non stop but cannot find a definite fix. Some say you can solder in a resistor by cutting the passlock wires and measuring it with an ohm meter and that should take care of it but I’d rather fix it the ‘right’ way. From my research it looks like the passlock sensor is on the ignition housing and it picks up the signal once it is turned all the way to the start position. Can anyone point me in the right direction? Do I need a new part (ignition switch, tumbler, key, housing etc) or do I look further into the resistor fix? 

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Buy a new ignition key switch lock cylinder with new keys to fix your issue and door lock cylinders if you don't want to carry 2 keys.  A poorly cut key or worn out one will cause this problem. - https://www.ebay.com/itm/NEW-GMC-GM-OEM-IGNITION-KEY-SWITCH-LOCK-CYLINDER-2-DOOR-LOCK-CYLINDER-2-KEYS/351956362573

Edited by 19Sil
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I had a 2005 Colorado with same issue dealer had to replace ignition  switch, there was some kind of piece on end of switch body with two wire plugged into it. All I needed was that part but you had to buy the complete switch assembly to get the needed part,  if the padlock icon on dash that lights up with all the other ones when switch is turned on was showing locked it would turn over but not start. This could possibly be the problem as I would assume they used the same ignition switch. Never did it while running, was always when trying to start it. I am assuming the pass lock you are referring to is the piece on end of switch body that I had to replace.

Edited by Booger T
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I was leaning towards the key/ignition tumbler myself so it helps to have more opinions on it. The original key got stolen a couple of months ago when buddy went to warm it up one cold morning and a stand up citizen took the opportunity to hitch a ride in it. He dumped the truck about three blocks from his house but took the original keys. I spoke to my buddy today and he said he has never had an issue with it before so that was my guess is that the spares were of suspicion.


The only thing that steered me away from blaming the key is that even though I had to jiggle it, it would eventually turn over and let me start it. I will order a new key tomorrow through the dealership by vin. If not, I will try the ignition switch cylinder and hope for the best. 


I love this truck and my buddy has owned since it had 81K. It still runs great, plenty of power but its forcing me to believe it is not reliable because it has left me 'stranded' three times now in the last month. It did it this morning but I did the relearn procedure and it fired right up after the first ten minutes. Thankfully I had no where to be but the last two times made me late for work and left my girlfriend and I in a parking lot for 20 minutes.


In case anyone searches and is wondering what the relearn procedure is, this is what I do and it has worked every time so far:


-Attempt to start truck - PASSLOCK symbol on IPC will start flashing and truck will not start

-Roll off the key but leave it on the "ON" position

-Passlock will now either be flashing or solid

-Set timer on your phone for 10 minutes and either sit in there and wait or come back before it goes off

-After 10 minutes (pretty much on the dot) the PASSLOCK light will now be off

-Now turn key all the back to the off position for 3-5 seconds

-Attempt to start the truck - Sometimes it starts on the first try 

-If no start, proceed to do it all over again up to three times.

Edited by SouthPawCO
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If it happens to be the ignition switch I would bet it is the plastic piece on the end the wires plug into that is the problem, if that's the case you would not need new keys but you would have to buy the complete ignition piece to get it. not sure but I think that the part the key went into was reusable and didn't have to be replaced. If new key doesn't solve the problem that would be the next place I'd focus on.

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Well I called the dealer this morning to get the key ordered and he suggested that a new key probably wasn't the issue. I was thinking last night at 217K, the original key my buddy had been using probably wore it self into the ignition lock cylinder over time. That is why the spares are having a hard time turning because they are 'new' and sharp. He suggested that I replace P/N 88965342 - IGNITION LOCK CYLINDER HOUSING W/PASSLOCK SENSOR. With my discount at work its $87.65 which is cheaper than NAPA has it and it's OEM. I think I am going to try it today and pray for the best. I hate gambling with $88 but the light turned on this morning on my way to the gym and on my way to work. I feared if I turned it off, it wasn't going to start.


One thing to add, I noticed it appears to have an aftermarket alarm that is missing the brain box. I called my buddy and he said years ago he had it installed but it was giving him issues so he took out the brain module. He said he never had an issue with it not starting but now I am wondering if it has bypass module in it. 

Edited by SouthPawCO
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Well here is some fun new info...


As previously stated, the security light turned on this morning on my way to the gym and on my way to work. I never shut the truck off till I got to work because I was afraid it wasn't going to start. I got to work, shut it down and it restarted no problems multiple times. My buddy was here so I talked with him some more and he said he had an aftermarket remote start put in years ago but took it out after it out after it wasn't working correctly. So I took apart the steering column covers to reveal the passlock wires. I disonnected the passlock plug right at the sensor and tried to start it thinking it would not..... to my surprise it not only started but I took it for a 10 miles test drive and no security light was on. I got back to my shop, turned it off and start cycling the key. This time, the light turned on with the plug disconnected but it still started. I played around with it and found out when the plug is connected, it would start and the light was off. With the plug disconnected, the light was on but would still start. This now leads me to believe that there is a passlock module bypass somewhere and that may be the issue. I am going to try to find it today on my lunch break but I called Car Toys and they said they could remove the alarm for about $90 and return it to OEM. I think that would be my best bet at this point to rule out any additional issues. 

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I keep posting this in hopes that someone down the road may be able to use this information because I love forums like these. They provide so much information and can be very helpful. I can't count how many times I have used them as a 'forum mechanic' that shops hate but I direct them to a lot info that they may over look. Here is some more information.


We have a Snap-On Solus at work so I hooked it up to check codes in the BCM. None were currently present but it had two history codes:


B2948 - Security System Sensor Power Circuit High

B2960 - Security System Date incorrect But Valid


Now you may ask WTF do those mean? I found this with my google fu





This code sets if the BCM detects battery voltage on the sensor circuit (yellow wire) for more than 1-sec AFTER the ignition switch has been turned to OFF. This is basically a short to battery from the sensor supply circuit (white wire) to the sensor circuit (yellow wire).

Test for a short to battery with the ignition switch in the OFF position.

If the BCM sees battery voltage with ignition turned to off, it will set this code and turn the SECURITY light on steady.

The BCM will still allow the car to start but will store the code and keep the SECURITY light on until it no longer detects short to battery. If you fix the short to battery, cycle the ignition switch from OFF to ON. The BCM will then enter the code as a “history” code and store it there for the next 100 starts.



The BCM is expecting a certain voltage value from the sensor based on its last learn cycle. The BCM compares the voltage value to its stored value every time the ignition switch is rotated from ON to CRANK. If the BCM sees a different voltage value from the sensor, it will not send a coded message to the PCM and the vehicle will not start. The SECURITY light will FLASH.

If the vehicle is running when the BCM detects the incorrect voltage, it will enter fail enable mode and allow the vehicle to start and run and will turn the SECURITY light ON steady. The code will clear once the BCM senses normal voltage, but will store the code as a history code for the next 100 concurrent ignition cycles.



I cleared the codes and began more research. This lead me to this site: https://www.dewitzdiagnosticsolutions.com/gms-theft-code-b2960-key-code-incorrect-but-valid/. From here, I gather that I have not been delaying starting the truck or waiting for the security light to go off. I hop in, I put the key in and crank. Being an old girl like herself, I don't think I am giving it enough time to see what key is in the cylinder and if it's ok to start. I believe the PCM is seeing that the key turns the tumbler but did not have a chance to see if the OHM is satisfying it. If not, I will try replacing the lock cylinder and after that, the passlock sensor. 



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Well that didn't work... lol. I leave the key in the position on till the security light turns off but it turned back on on my way to work. Truck started and ran fine but back to the drawing board. I didn't realize the damn steering wheel had to come off to replace that housing w/ sensor so I may look into the resistor fix. 

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VOILA! Problem found, fixed and on it's way!


Long story short, One of the yellow wires coming off the passlock sensor, through the steering column, to the bcm, had been cut. I couldn't see it had been cut because they tucked it in the with the rest of the harness. After following those, I found where they had put in two resistors to bypass the passlock system. After opening up the electrical tape, there it was, two resistors with one of the ends snapped off. I took all of it out, soldered in a new piece and sealed it up. Started right up and no security lights!


Hard to see but the broken yellow wire:



Broken resistor inside the electrical tape:



The poor solder job. It was really tight in there trying to hold those damn wires:



The culprit:


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  • 4 years later...

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