Robo Tech’s GM Passlock Bypass
Robo Tech was called to a 2002 Pontiac Grand Am, with a 3.8 liter engine. The tech said
that as he was driving, the "SECURITY" light came on. There did not seem to be any effect
on driving. After the road test, he re-started the car without any problems, and the security
light was not on. Later on, he started the car again, it ran for a couple of seconds,
and then stopped, with the SECURITY light flashing. The car then would not re-start
anymore, and the SECURITY light remained on.
The information database said regarding the security Passlock, after attempting to re-start
the engine, if the SECURITY light flashes or stays on, wait ten minutes with the key
in ON until the light goes off. Then, turn the ignition to the OFF position before attempting
to start the engine again. This information worked, and the vehicle started.
Unfortunately, a few weeks later, the tech said he had to go through the same procedure
to get the customer's car started. At this time, the customer said he wanted the Passlock
bypassed, and not repaired. Well, I am Robo Tech and don't really get
involved with Jerry rigging automobiles. It is beneath my intellect! So, I decided to
call in my cousin, Roby Martin, an expert at nothing, axcept cutting wires.
Hello, I am Roby Martin. Follow me on this one, as we perform a high class GM Passlock
bypass. It turns out that, the most common culprit
for Passlock faults is a Security module in the ignition switch, but there are several
other possible causes for this Passlock problem. Anything which causes the apparent resistance
in the circuit to change by a significant amount will trigger the security system, and
cause the car not to start. This means that before cutting any wires, you should make
sure that something much simpler is not the answer.
Once I determined without a doubt, that the problem with the system was a faulty Passlock
module in the ignition cylinder, I decided to then bypass the system using a pubic hair,
oh no, I meant the resistor method. This would make the system behave as though there were
no problems at all. The Passlock Security System is quite simple.
When the Body Control Module is programmed, it measures and stores the value of the signal,
on the Yellow Wire on pin 6, of the center connector, using the black wire as a reference.
From then on, each time the car is started, the Body Control Module checks to see if the
signal on the yellow wire, matches the stored value. If a key is not inserted into the ignition
switch, and the lock cylinder is not rotated to the on position, the value of the signal
will be incorrect. The Body Control Module will then send a signal to the Engine Control
Module, telling it to shut down the fuel injectors. The resistor is embedded in the Passcode module,
which is part of the ignition switch cylinder. Any key that will allow the cylinder to be
turned to the on position will work, and the only condition that must be met, is that the
cylinder must be turned to a position where a magnet engages a hall-effect switch, which
connects the embedded resistor to the system, allowing the Body Control Module to read the
signal value on the yellow wire and determine if it is correct.
You can avoid paying 300 to 500 dollars to change the lock cylinder, by performing a
simple modification on your vehicle. But before you start, you should make sure that your
vehicle is one that uses this system. The information database should read, after attempting
to start the engine, if the SECURITY light flashes or stays on, wait ten minutes with
the ignition key in ON, until the light goes off. That phrase is the key to knowing that
your system can be modified in this manner. I knew that this procedure worked on this
car, so I then proceeded with the modification. I started by disconnectin the battery, then
disconnected the Grey center connector from the Body Control Module, and pulled it down
so as to access the wires that go to the ignition cylinder. Pin A6 of the connector will be
a yellow wire, and pin B6, which is directly opposite, will be a black wire. These are
the two wires I was going to work with. Here you can see these two wires issolated.
I then stripped the insulation off about half inch on the black wire, leaving it bare so
I could solder to it. Then, I cut the yellow wire about 4 incjes from the connector, and
stripped about an inch of insulation off the end of the wire, which goes to the connector.
I also taped up the other wire end, bent it back, and push it back into the bundle out
of the way. I then slid a 2 and a half inch piece of shrink
tubing over the yellow wire, so that I could later use it to cover the resistor I was about
to solder into the circuit. I took a 2.8 Kilo Ohm one quarter watt resistor,
and wraped one end of it around the stripped part of the black wire several times so as
to have a good contact and then soldered the joint. I arbitrarily chose to use a 2.8 Kilo
Ohm resistor. We will later be programming the Body Control Module to recognize the resistor
we chose, so it doesn't matter what size you use. It can be anything from 470 ohms to 11800
ohms. I then wraped the stripped end of the yellow wire from the connector, around the
other lead of the resistor, and solder it in place.
I also slid the shrink tubing up so as to cover the resistor, and applied some heat
then black electrical tape to insulate the bare part of the black wire where I soldered
the resistor to it. After taping the resistor I plugged the grey
connector back into the Body Control Module and re-connected the battery negative terminal.
Then when I tried to start the car, it started and then stop after a second or two, with
the Security light on. That's OK, because now I had to re-calibrate the Body Control
Module to the 2.8 Kilo ohm resistor. I did that by turning the Ignition key to
the off position, then turn it to the on position. The security light came on, so I waited about
10 minutes with the key in ON until the light went off. Then, turn the ignition to OFF before
attempting to start the engine again. At that time, the Body Control Module would have memorized
the new value for your resistor, and the engine started.
This bypass procedure went well and the customer forgot about the Passlock problems forever.
By the way, to get better access to the wiring on the car, I also removed the Glove box.
This was quite easy, just two screws at the top edge, and one on each side hold it in
place. But, make sure to carefully disconnect the glove box light, and re-connect it when
re-installing. This case study shows that Robo Tech is not
the only smart dude on the block. Roby Martin can also solved automotive issues.