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Fellas im looking at replacing my BCM. All the issues im having are point towards it being the culprit. Is there anything special involved....such as gm dealer involvement?
Yes, I meant VATS. BCM is measuring voltage coming from sensor on ignition switch. if you replace BCM it should learn this voltage, no matter where it coming from actual sensor or imitation/bypass. PCM also should learn code for BCM. It all can be done manually. Or you can remove VATS from PCM using HPtuners.
Yes, I meant VATS. BCM is measuring voltage coming from sensor on ignition switch. if you replace BCM it should learn this voltage, no matter where it coming from actual sensor or imitation/bypass. PCM also should learn code for BCM. It all can be done manually. Or you can remove VATS from PCM using HPtuners.
VATS doesn't measure voltage, it measures the resistance of the pellet that's on the key! only the fuel shut off can be removed from the PCM by tuning software, but the starter won't work because it's controlled by the BCM.
Diagram I have posted is for 1999 Trans Am. And as I understand the original poster is talking about this car. So, according to Alldata it has no resistor in key. First GM immobilizing system was using such resistor. In this case it is special module with the only function measuring resistance (by measuring voltage drop) and sending to PCM 50 Hz square wave signal if it sees right resistor. In this case if module is dead or you are lazy to try 15 different resistor to substitute the lost one, you can easily start car using primitive wave generator. Old GM MAF sensors can do the trick. It also can be done with long screw and connected to car ground and wire coming from PCM. When you rob wire from PCM against screw thread for few seconds while somebody cranks car you can start the car. After engine run and signal stops logic in PCM will assume system is defective and car will start every time without signal imitation. Until you disconnect power from PCM.
More sophisticated GM systems are using setup similar to the one, schematic I posted. In this case you can reprogram BCM for sensor with different resistance. But it also needs PCM-BCM relearn when modules replaced. No special tools needed but with Tech2 and TIS it is faster.
I had 15 98-02 f-body cars in the last five years and ALL had the resistor pellet in the key! you can not reprogram the BCM for a different resistance, you must match the resistor pellet in the key to the stored resistance in the BCM's ROM.
I had 15 98-02 f-body cars in the last five years and ALL had the resistor pellet in the key! you can not reprogram the BCM for a different resistance, you must match the resistor pellet in the key to the stored resistance in the BCM's ROM.
As I told, I got information from Alldata. You might be right and I might be wrong. I am repairing cars for living for last 25 years and I am not relying on my memory, only on manuals.
The OP never stated that he was having a starting/VATS problem leading to his conclusion to replace the BCM. He just mentioned unspecified "symptoms". Until he reports what symptoms he's experiencing, further discussion is moot.
I'm moving this over to the General Maintenance and Repairs forum, as whatever his problem is, it is not an external engine issue.
any new bcm will automatically program to the resistance of the ignition key being used at the first ignition ON cycle. this can only be done once for the life of the bcm.
the bcm can only be programmed to one igntion key resistance. all ignition key resistances must match.
a new bcm is not programmed, with new bcm installed reconnect neg. battery cable. insert ignition key and start engine. observe security lamp for following
- lights steady for 5 seconds then goes out, this means new bcm programmed properly.
- flashes at rate of once per second until ignition is turned off, this means bcm did not program properly and have to do fault check.
if you buy a new bcm from dealer and they say "they must program it" and it will cost an extra $100 for that service charge, they are F.O.S. if the bcm is truly new and unprogrammed, then all you do is start the engine. at most you reprogram your key fob to unlock the doors and rear hatch.
The issues I am having consist power windows not working from time to time, alarm going off after being armed and occasional radio inop.
Sounds like the BCM- try the soldering mod first, that fixes them most of the time. Pull the BCM down from behind the dash on the passenger side...open it up, take a look at it and locate the 5 points outlined in the picture attached. Touch up those points with some solder and a soldering gun and 9/10 that will fix your issue.
If that doesn't work, you'll need to buy another bcm- you can get them from the junkyard, but you will need hptuners to bypass vats (and it will work, that is how my current car is running)
If you don't have hp tuners, you can also do the 99 cent vats bypass if you know the resistance of the key that came with that car. You'll have to google that fix because I cant remember all the steps off the top of my head- it is basically snip a wire and solder a resistor in between the two ends though...
03-12-2016, 10:02 AM
