General Motor’s Theft No Crank/No Start Security Relearn
I am sure many of you have had a GM towed in as a no start and when you go out to try to start it, it fires right up. Well we know many things will do this like the fuel pump, ignition components, starter, etc. So you then go and scan the vehicle and you get the code B2960 (key code incorrect but valid). I also get a U1000 code a lot with this code which may be related, may not be. The information I give from here is from what I have seen and is my opinion for some of the problems that cause this code.
When I get the code B2960, I will look through the security data pids for any problem. I will see if there are any other codes in any of the other modules. I will check the key code voltage and see if it matches what it wants to see. What I do next if there are no other codes that I think relate to the no start, the key code voltage is correct, no other security data pid problems, and after clearing the code it does not reset and the vehicle starts. First thing I will do is test the battery electronically with my midtronics tester and then load test it. Next I will check power and ground connections. My next step is the most important once you get this far. I will call the customer and ask them a few important questions; when did you see the security light and do you turn the key to on before you start your vehicle. If the customer says the security light came on while driving and the no start happened later, then my diagnoses will go a different direction. If the customer says the light was flashing after the no start or they say they didn’t notice the light, I will continue to proceed in this direction. The next answer I hear is usually the same and I believe is part of the cause of the B2960 code.
“Wait to start? I just turn the key until it starts.” This is the biggest piece of the puzzle for me. Let me tell you how the Passlock(TM) lock cylinder works from Alldata. When the correct key is used to start the vehicle, a magnet on the lock cylinder passes close to the Passlock(TM) sensor within the ignition lock cylinder case. The magnet activates the security hall effect sensor in the Passlock(TM) sensor which completes a circuit from the security sensor signal circuit through a resistor to the security sensor low reference circuit. The BCM will measure the voltage on the security sensor signal circuit and compares this voltage to a previously learned voltage. If the voltage measured is within a valid range, the BCM will send a class 2 message to the PCM to enable vehicle starting. If the voltage measures is not within a valid range, a class 2 message is sent to the PCM to disable vehicle starting. Think about everything that happens when you turn the key on, all the modules are powering up, radio turns on, headlamps and light might come on, all the sensors are getting there reference voltages, etc. Now think what happens when you turn the key to crank, a lot of components are now turning off like the radio, hvac system, light, etc. and the starter starts to draw a couple hundred amps. Now think what happens when all of this occurs within a 1/2 second when the customer turns the key straight to start. Can you see where your voltages are moving all over the place in a very short time how the key code voltage may be off .2 of a volt and cause a no start and the B2960 code. Now lets say the magnet is a little weak or the key cylinder is a little worn and how this can happen very easily.
90% of my customers will be charged a diagnostic fee for what I have checked. I do a key relearn which involves 3 ten minute key cycles and I tell them to turn the key to on for a second or 2 and then to crank. I will never see them back for this problem again. The other 10% have a faulty key lock cylinder, forget to turn the key to on first, or have some other problem with the system. Of that 10%, a new key lock cylinder sensor will fix 95% of them while 5% of those 10% have a different problem. If I do not replace the key lock cylinder sensor right away because the customer wants to try turning the key to on for a second before starting first, I always let them know that if it does happen again where they get a no start, to turn the key to crank and then release without turning the key off, wait 10 minutes for the theft light to stop flashing, turn the key off 5 seconds to put the theft system into bypass mode. This gives them the chance to start the vehicle, not be stranded, and to save a towing charge so that I can fix the problem correctly for them. This is just my theory on this problem and this procedure continues to work for me.
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