A defective Crank Position Sensor most certainly can prevent the engine from starting, but that has nothing to do with VATS. There are 2 scenarios with VATS regarding a
flashing SECURITY lamp, and both point to a defect in the circuit preventing the key from being seen. Which scenario fits? We can't answer that. Read on, and pay special attention to what I have emphasized. IF, BIG
if, the SECURTIY lamp has always flashed and the engine ran, sure, consider the crank position sensor. A lot of aftermarket electronic components these days are garbage and defective out of the box or have a high failure rate. However, if the flashing began with the no start condition, the condition and lamp
are related.
You have 3 paths available
- Download the Factory Service Manual (free) and diagnose the crank position sensor / Read shbox's VATS page and diagnose VATS.
- Pay your Mechanic to diagnose and resolve it.
- Start randomly replacing parts until you get the engine to fire.
From the
authority on VATS (shbox):
4th Gen LT1 F-Body Tech-PassKey/VATS
Abnormal Operation
If the key pellet is the wrong value, the TDM will not send signals to allow the starter to engage or fuel to the engine. The TDM will shut down for ~3 minutes and the SECURITY lamp will remain lit with the key ON or OFF. When the ~3 minute timer has expired and the key is cycled from OFF to ON, the TDM timer is reset. If you try a key with the correct pellet value, the engine should start and run. SECURITY lamp should be off. If there is still a problem with reading the key, the TDM will light the SECURITY lamp and start the ~3 minute timer again.
If the sensing contact circuit is open or shorted (cannot read the key) or a defective key is used at the time the ignition is turned ON, the SECURITY lamp will flash at a rate of once per second and the engine will not start. No three minute lockout will begin.
The SECURITY lamp will also flash at once per second if a new, unprogrammed TDM is installed and there still is a defect in the key reading circuit. The engine will start in this condition, though.
The lock cylinder circuit is continuously monitored. If a fault lasting 1 minute is detected, the SECURITY lamp will light. If the fault then goes away for 1 minute, the lamp will go back off.
If the system detects a fault with the lock cylinder circuit after the engine is already running, the SECURITY lamp will light. The engine will be able to be restarted. This is called “fault enable mode”. (The system saw a good reading from the key at one point during a previous ignition cycle before the failure. So, it considers it a problem and not someone trying to steal the car.) When in fault enable mode, PASSKey protection is disabled until the problem is repaired. Once repaired, the SECURITY lamp will go out about 1 minute after the key is turned on. Fault enable mode will not shut down the engine while you are driving.
The Factory Service Manual will assist you in diagnosing the Crank Position Sensor. You should only need a $10 Multi-Meter (volt-ohm meter) for this. Start here if the SECURITY lamp always flashed before but the engine still started. Otherwise, the "key sensing circuit" is open, as in, something isn't making contact.
While both scenarios point to a "problem in the circuit", they are both key related. The little "pellet" in the key is nothing more than a resistor, and it would in my opinion be extremely rare for a resistor to just die electrically in a manner that creates an open circuit. ...but if you probe it with the multi-meter and get no reading what-so-ever, there you go. Dead resistor. Using a multi-meter and the information at shbox, this is easy to determine.
It is more likely though that the resistors contacts on the key have worn down so far they physically do not make contact with the ignition barrel. No key contact with the barrel would be an open circuit as the key
completes the circuit. A worn ignition barrel that can't contact the key? Same thing.
Installed something aftermarket and rooted around in the dash? Maybe the connector for the ignition barrel came loose and after some time and vibration, open circuit. Broken wire? Open circuit. Regardless of which "flashing security lamp" scenario you fall into, the Theft Deterrent Module can not "see" the key's resistor. ...that is the thing to take away here. While in scenario two, the engine starts, the key's resistor is still not completing the circuit for whatever reason. Hell, you could have bought the car with scenario two being a thing and over time progressed into scenario one. Hard to say.
VATS seems like an intimidating system and most belittle it, but it's not complicated at all. Read over all the VATS information at the shbox site and follow the links. The mystery and magic of VATS quickly disappears. It really is a straight-forward and easily diagnosed system once you get past the intimidation of it. ...and the quickest way to get over it is to
learn about it.
If you read though
all the VATS information, not only will you be able to diagnose the system, you'll immediately know how to "bypass" it very cheaply and easily should the culprit be the key or ignition barrel. That is if you want to bypass it. Should you want to keep the VATS functional, you'll at least know what you need to replace.
As to no codes for the crank position sensor, unfortunately, it is possible for things to fail without setting a code. Not very likely with that particular sensor, but not unheard of either. This is why I point you to the Factory Service Manual. It will have an easy to follow flow-chart to diagnose the sensor. Where you should begin looking first though hinges on if or if not that SECURITY light was flashing before the no-start condition. Either way, it's easy stuff if you have the right tools and resources. No need for a mechanic unless you don't want to be bothered with it, but having a scan tool and changing the crank position sensor yourself suggests to me that you do want to learn and take care of this, so grab that factory service manual regardless. Even if you don't need it this time around, you'll appreciate having it next time when you do.
...and if you don't have a multi-meter, get one now, because if it has a wire going to it then a multi-meter is required to diagnose it. The Factory Service Manual and a Multi-Meter really are the two most valuable tools you can have if you want to keep these cars going. ...one of them is free, and the other is under $10. No excuse not to have them.
Good Luck!
