So I mistakenly gave you some bad information, BCM's are programmed or flashed to match them with the correct key resistance value, so maybe at some point in your car's life the BCM was replaced, this means that the VIN number which calls out what number key should be used is incorrect. So you do have two choices, connect a potentiometer and determine what resistance will allow the car to crank or send the BCM to have it flashed to key #12. The security light will blink because the key resistance is not correct, therefore the BCM will not connect the negative side of the TDR coil to ground. You should hear the TDR click when you try to start your car. The TDR relay is located above the BCM and is the relay that sends power to the energize the starter, making sure your car is in neutral"m6" or park"auto",insert a heavy gauge wire between the thicker red wire and violet wire on the TDR relay socket, your car should crank over.

 

If this is a way that I can confirm my issue is with the key I will give it a try.
I do hear teh TDR click when I go to start teh car. So do I remove teh TDR socket and run a wire into where it plugs in? Or do I modify the TDR and then plug it back in? If this works can I just leave it this way and have the problem be solved?

 

So you can just take a jumper with the TDR plugged in, if the car cranks over your problem could be the TDR needs replacing, if it fails to crank you could have a starter solenoid problem and or bad cable connections on the battery or on the starter solenoid. But it's good news that the TDR is clicking that means there is nothing wrong with your key.

 

Man I do appreciate your help. But it would have helped for me to know that the instant I bridged the red and the violet wire that the car was going to immediately begin to crank. I was laying there with the car in gear.

Anyway.... So when I bridge those two wires teh car begins to crank. I tried inserting the key and turning on hte ignition, then crossed those tow wires. The car cranks but has no spark.

So what does this tell me? My starter cyl is fine ad is my starter. Security light stayed on.

I think I have the wrong resistance for this car. What can I do next?

 

In all fairness, he did tell you not to have the car in gear, although he omitted to tell you why . Look at the schematic below to further clarify things.



I'm a little confused... You mentioned that when you turn your new key to start, the car doesn't crank, but you can hear the TDR click. Is that right? If that is the case I would suggest to test the TDR. With the wrong key the TDR shouldn't click.

If that was not the case and the TDR doesn't click, then chances are you have the wrong key. I would suggest again what I mentioned above in Post 15: get the correct resistance value and take it from there.

Was your car fine until you lost your keys?

 

Yes make sure it is the TDR you hear clicking, have somebody try to start you car while you hold the TDR and can feel it click.

 

Before I lost the key the car started just fine.


Yeahit greatly helps to have an old key to measure the resistance (didn't think that'd be supplied by the VIN but I don't work at GM) on the key's pellet. --- I don't have the original kkey, so i am a no go there.

What I would do, is take apart the consol and get to the VATs wiring. They are the two white wires that go to the resistor pellet on the fob. I'd use multiple resistors or an adjustable 10k potentiometer to see what worked and then measure with a DMM.

Not sure if I understand what you are asking me to do here. Can you please break it down to a step by step?


FWIW: The car seemed damp in the inside. It had been raining a lot. And even though it has a car cover on it, I still get a damp type of smell.

 

I thought I heard something click down there but I just has my neighbor turn the key while I held the TDR and I felt No click.. Does this imply that I have a bad TDR? Is this a dealer part or part store?

 

That, plus the fact that it cranks with the TDR jumped, seems to indicate a bad key (VATS)

 

Like I started with. I think the dealer has given me the wrong key. How can I test my VATS to find out which resistor I need?

 

Basically is this, as mentioned above:

Take a look at the schematic below to better understand what you're doing.


You need to access your ignition switch. Disconnect connector C3 from the ignition switch. Those are the wires that go to the "Key Resistor Sensing Terminals" and you need them to directly connect to them a resistor that will take the place of your key's pellet.

It's a trial-and-error process, but only with 15 different possibilities. You either get a resistor (or combination of resistors) for each of those 15 possible values, or you get a variable resistor (potentiometer or rheostat) of, let's say 12 to 15 K-Ohms to cover all 15 values ( ).

With a variable resistor is easier. Using your multimeter you set the variable resistor beforehand to the first possible value from the table and then connect it to Connector C3 (that you previously unplugged) and insert your key in the ignition switch and test it (try to start the car). If it doesn't work, disconnect the variable resistor, set the next value and keep on going until you get it. It sounds more complicated than what it really is

 

This is the only way you will find out which key will be the correct one.

 

I believe Code B2721 indicates what is wrong. I am making an engineering assumption here because the system worked until the OP lost his key and had it replaced. There are no other security system failure signs other than the codes for the PASS Key.

There are two codes related to the wrong resistance. B2721 and B2722, B2722 relates to a ground being applied to the circuit and dragging the resistance below the valid range.

B2721 Indicates the resistance level sampled at the BCMs PASS-Key® input circuit is one of fourteen valid but incorrect resistance ranges, signaling an invalid PASS-Key® detection. Thus the key is valid but the wrong resistance is present. This could have come about due to an earlier repair in the car's 22 year life time. Maybe one of the original two keys was lost/stolen so they reprogrammed the BCM to accept a different key. Depending on where that was done GM may not have a record of the correct resistance.

There are a couple of ways around the problem. One of them is to do some experimentation to determine the correct resistance value and order the correct key while the other is to reprogram the BCM to accept the key you have now. Then purchase a second key to go with it so you have a spare. Reprogramming may be the best way to go since you don't want somebody to find your old key and use it to start your car.

I am attaching the 1998 Factory Service Manual Diagnostic Procedure to this post. I also included the BCM reprogramming procedure after the diagnostic.

OP: Your one current B code also indicates you have problems with the air handling actuators in the HVAC system. This code won't tell display that you have a problem you have to notice something isn't working correctly before you find the code. Maybe the HVAC hasn't been working as well as it should in conditioning the air inside the car.

Bill

 

Did you measure the pellet in the key the dealer supplied just to verify it really is a 12?

 

He did. That is why I think the dealership ordered the wrong key or the wrong one was delivered to them. With a 22 year old car there is a high likelihood the original key was replaced with another key with a different key/pellet and the GM records weren't updated to show a new key resistance was programmed into the BCM.

Bill

 

Yes, GCG's last post is how you'd do it. When you take off the plastic surround for the key, there are two white wires on a connector. They are small so don't snap them.

Use resistors or the potentiometer. Between each resistor value, or between each slight turn of the potentiometer, wait 3 minutes before trying again. I understand the PCM or BCM has a 3 minute digital clock timer inbetween each time or else you'll be locked out or have the "Pull key" message. When your car finally starts and stays running, remember the resistor value or measure it with a multimeter set to OHMs

What GM used back in the day was a box that did this same procedure. It'd generate a resistance, wait 3 minutes, and repeat until the desired value was found.

When the desired resistance originally set by the BCM is met, it completes the circuit and sends a 5v 50Hz signal for the fuel injectors to start spraying

 

Does the fact that I have an LMC5 thing attached have any effect on this process? It ties in at the BCM.

 

Can anyone explain why we aren’t contacting the dealer to fix the mistake?

 

Order this.
https://www.ebay.com/itm/The-Install...8AAMXQBuNQ4yl3

Wrap tape around the key pellet.

Jumper the two wires in this video one resistor at a time until you find the one that lets the car start.


Get key that matches the resistor value. Good luck

 

In response to next to last reply, the dealer, yea I know I am defending the dealer, they sold him a key based on VIN information, but something has been changed on the car like different keys and possibly re-flashed BCM. I like the idea of buying the resistor pack which contains all fifteen resistors, and plugging them in at the BCM, but make sure you place tape on the keys resistor chip, because you are placing two resistors in parallel if do not place tape on the keys resistor chip. And one final thing the LMC5 is not the cause of the problem.