Bypass BCM/PCM on 98 VT

[barrystyle]

Hello all,

Have recently had the BCM in my daily VT let go; basically pop my key in, crank car over, the engine does start and a second later cuts out (all the while, the red light for immobilizer is rapidly flashing).

Have managed to find that neither key disarms the system anymore (even after replacing the batteries) and am stuck with the classic 'mechanically fine but electronically inhibited' car scenario.

Have built myself a RS232-TTL OBD1.5 adapter for the car, to find that I will need to order a memcal to write the VT rom to with VATS disabled. Either that or an EEPROM burner and UV light to reprogram a normal EEPROM (standard chip?).

Anyway; i've found that it all boils down to the BCM (once satisfied) sending a signal to the PCM to allow the engine to start. Before I continue; I am aware that these sort of posts are frowned upon - however I've owned the car since 2008 and being without a daily has caused me considerable grief this and last week.

The guys in the American GM forums have made mention of a device that can be built to generate a signal that tricks the PCM, roughly same year as our Commodores. I'm not going to describe the device for above reasons, but i'd like to know basically would this same 'device' work for our cars. I've got the parts to built the circuit and just don't want to potentially fry anything.

Or short of that - can someone test the BCM-ECU wire and i'll confirm what the volt/hz is meant to be?

james

[Dylan]

If not having full security feature doesn't worry you I'd have someone burn you a new memcal with VATS disabled. Can get a few performance and fuel economy gains to while you are going. Cheap and easy.

[barrystyle]

Appreciate the response; but have just been informed that the module will work on my car.
I will post when i've built the module for results.
Albeit staying vague, i hope this helps someone else out there avoid the drama i've had for the past 1.5 weeks.

Out of interest what does a programmed memcal go for?

[The1]

$35 for a new memcal, which also doesn't need uv erasing, just program on the burner, can burn stock tune with vats off no extra cost.
http://pcmhacking.net/forums/viewtopic.php?f=14&t=3650

Vats in the memcal waits for the OK from the BCM so it can enable the injectors, with vats off it just enables the injectors.

[antus]

Our cars do not use a frequency signal like the US models you are comparing. The BCM is married to the PCM and they talk to each other digitally over the ALDL bus. A VATs disabled memcal is the simplest way to work around your problem (see the1s post, and he might be able to help with the vats disabled tune as well?). The wire that is most likely your problem is between the ring under the key and and the bcm. You just need to check continuity and make sure the key is connecting to it properly.

[Tazzi]

Antus is spot on.

Not a mater of simply setting the correct frequency. Cheapest and best way is to go down the memcal route.

[barrystyle]

$35 for a new memcal, which also doesn't need uv erasing, just program on the burner, can burn stock tune with vats off no extra cost.
http://pcmhacking.net/forums/viewtopic.php?f=14&t=3650

Vats in the memcal waits for the OK from the BCM so it can enable the injectors, with vats off it just enables the injectors.

Hey The1 - just took a look at your PCMHacking Hardware&Software guide - very informative.
So the standard 27C010 is non-removable from PCM; requires de-soldering to install a different chip?
I'm yet to actually crack my PCM open, but from the looks both standard and your replacement are 32-pin, can i ask what the adapter is for?

I obtained a 32pin SST 5V EEPROM, flashed a VT 128k ROM (VATS DISABLED) onto it using an Intel PRO 100 Network Card and flashrom (https://www.flashrom.org/Flashrom), read it back and verified fine. Will find out after work if it goes

[Jayme]

in a VT, you can pull the memcal from the pcm, then lift the lid off the memcal, peel the silver sticker off the Eprom window, sit the whole thing into a UV eraser, erase it, then plug the1s adapter into the memcal, which will give you 32 pins to stuff into the zif socket of your eprom burner and burn your new tune.

[barrystyle]

Hey guys,

Had forgotten about this for a while, as I got my Starion running again to get me to work and back each day.

I started to concentrate on the BCM itself - this seems to be what is at fault. I built a small parallel-port SPI reader and dragged the contents off the 93C46-style EEPROM off the BCM; but it leaves me stumped - I can't see my VIN number (present in every other dump i've seen). I've also tested the reader with a few other 93C46 series chips i have lying around (NE2000 NIC, SB Live); and all consistently read/write correctly.

Just want to confirm a few things before i attempt a write:
a) What is the starting byte (or offset if you prefer) that the VIN should appear at? (i've seen 0x1E mentioned a few times)
b) Also just making sure I've got the right chip (http://i.imgur.com/3fs8UM0.jpg BCM facing rear of pcb).
c) I've read that the chip can be read directly in situ - however ive desoldered VCC and lifted from the pcb, then power the chip with 5v from the parallel port just to make sure im not powering anything else up on the BCM. Should i leave it connected to board?

The car itself cranks over, but as soon as the motor starts it cuts out (injectors/VATS as The1 pointed out).
BCM/PCM are clearly ok with it - central locking, indicators etc all work fine, no radiator fan coming on when key set to acc.

What am I missing?
james

(additionally: i've got a old keyfob from a mate that works well, have cleared it with FF and back to 00 few times consistently, if i were to use it as a new key - what offset would I read the 'code' off the BCM and write it to the key? key appears to have 4 bytes at the start, then a few FF's, followed by the 6 hex digits which are supposedly the code?)