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BigBob
BigBob, Shop Manager/Technician
Category: Car
Satisfied Customers: 4837
Experience:  Shop Manager with 25 years experience
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the security light in my car keeps coming on what is the cause

Customer Question

the security light in my car keeps coming on what is the cause
Submitted: 7 years ago.
Category: Car
Expert:  BigBob replied 7 years ago.
What year, make, and model? Does it start?

Bob
Customer: replied 7 years ago.
2002 pontiac grand am it didnt but then i left it in the on position 4 fifteen minutes it started but it comes back on
Expert:  BigBob replied 7 years ago.
Very common the ignition cylinder passlock cylinder goes bad. You will need to test some voltages and do some ohm testing, here is the test.

1. Test voltage values of the passlock sensor and compare the values to the voltages found when the vehicle is a no-start.

2. Three wires at the passlock sensor to test.

3. Test voltage from the Black wire to the White wire, back probing with the sensor connected.

4. Should have 9.0v or higher at: IGN 0, IGN 1 and CRANK.

5. Test voltage on the Yellow signal wire.

6. Should have 4.7-5.0v at: IGN 0, and then a drop to a specific value should occur as the key is rotated to IGN 1 and/or CRANK.

7. Compare this voltage value to what is detected when the vehicle is a no-start.


If the values are different replace passlock sensor cylinder. Voltage drop on the Yellow wire will be different for each vehicle, as there are 10 different possible resistor values. In some cases, this problem is too intermittent to test. If that is the case, the most common cause is a defective lock cylinder housing and the rotating lock cylinder. If the car starts with the relearn the most common cause is the passlock sensor assembly is changing its resistance values over time, causing the voltage on the Yellow wire to change to the point where the BCM does not accept it as its learned value. A relearn may fix it for 6 months or 6 hours, however there is an underlying problem

Good luck,
Bob