GM VATS
Memcal Calculator
Got a resistor-pellet key you can't replace, or a dead VATS module? Read the 27C256 chip on your memcal, upload the 32 KB file, and we clear the VATS anti-theft bit and correct the calibration checksum — in seconds. Your own tune is preserved: exactly two bytes change.
Online VATS-OFF
Upload your memcal file
Instant file back
Supported memcal reads are patched and returned in seconds — no shipping.
Your tune preserved
Only the VATS bit and its checksum change. Every calibration table is untouched.
Corrupt reads rejected
We verify the calibration checksum first — a bad read can never be patched and sold to you.
No VATS? No charge
If your calibration never used VATS, we tell you and you pay nothing.
Three steps, no shipping
If you can read an EPROM, you can have a VATS-OFF file in under a minute.
Read the memcal chip
Pull a full 32 KB read of the 27C256 on your memcal. Read it three times and confirm all three files match.
Upload & verify
Drop the .bin above. We verify the calibration checksum and confirm VATS is actually active — free, before any payment.
Download & burn
Get the VATS-OFF file in seconds. Burn it to a blank 27C256 and install it with a Moates G1 adapter.
Which cars run online
These are the calibration masks the calculator processes instantly. Anything else, we do mail-in.
| Mask | ECM part | Applications |
|---|---|---|
| $8D | 1227727 / 1227730 | 1986-1993 TPI 5.0 & 5.7 — Camaro, Firebird, Trans Am, IROC-Z; 1990-1991 Corvette |
| $DA3 | 16159278 | 1992-1993 LT1 F-body — Camaro Z28, Firebird, Trans Am |
You read the chip, we return the VATS-OFF file in seconds with the checksum corrected. You're only charged after your file passes verification.
No programmer, a chip that won't read cleanly, or a mask we don't process online? Ship the module and we read it here, patch it, burn a new chip, and send it back ready to plug in. Covers the wider 1986-2005 GM VATS range.
GM VATS delete (mail-in)How to read your memcal
The chip is a 28-pin 27C256 on the plug-in memcal cartridge inside the ECM.
- 1. Pull the ECM and open the access panel. The memcal is the small cartridge under the cover. Press both latches outward and it pops up.
- 2. Get at the chip. A Moates HDR1 header reads the memcal without desoldering anything. Otherwise desolder the 27C256 with braid and read it bare.
- 3. Select the right device. Set your programmer to 27C256. If your file comes back 64 KB you were on 27C512 — wrong part, read it again.
- 4. Read it three times. Compare all three files. They must be byte-identical. These chips are 30+ years old and intermittent pin contact produces convincing garbage.
- 5. Upload the .bin. We verify the calibration checksum independently and reject a corrupt read before you pay a cent.
Programmers that read a 27C256
XGecu T48 / T56
ZIF · direct
TL866II+ / TL866A
ZIF · direct
Moates HDR1 header
Reads memcal without desoldering
Moates BURN1 / APU1
Read · burn
Willem programmer
ZIF · direct
Any 27C256-capable reader
28-pin DIP
Burning and installing it
You get a .bin back. Here's what it goes onto and how it goes in.
The chip
Burn to a blank 27C256. An AT27C256R is one-time programmable and cheap — buy a few, since a failed burn costs you the chip. A W27C257 is electrically erasable, so you can re-burn the same chip as many times as you like.
Your original factory chip usually cannot be re-used: most are OTP with no quartz window, and an EPROM cannot be rewritten without being erased first.
Installing without soldering
A Moates G1 memory adapter is the clean way in: the burned chip plugs into the G1, the G1 plugs into your memcal, and the memcal goes back in the ECM. It keeps the memcal's laser-etched resistor and knock packs — those cannot be duplicated — and bypasses the original soldered chip entirely.
That also means a damaged original chip stops mattering: the G1 ignores it.
Questions
Which GM ECMs does the online VATS-OFF do?
The 32 KB memcal calibrations: $8D (ECM 1227727 / 1227730 — 1986-1993 TPI Camaro, Firebird, Trans Am and 1990-1991 Corvette) and $DA3 (ECM 16159278 — 1992-1993 LT1 F-body). Every upload is checked before payment. If your calibration is a mask we do not process, nothing is written and you are not charged.
What file do I upload?
A complete 32,768-byte (32 KB) read of the 27C256 EPROM on your memcal, saved as .bin. Read it with any EPROM programmer — a TL866, XGecu T48/T56, or a Moates HDR1 header if you would rather not desolder the chip.
My read came back 65,536 bytes. Is that wrong?
Yes — that means your programmer was set to 27C512. A GM memcal chip is a 27C256, which is 32,768 bytes. Change the device type to 27C256 and read it again. The calculator tells you this if you upload a 64 KB file.
How do I know my read is good?
Read the chip three times and compare. All three files should be byte-identical. These chips are 30+ years old and often pulled from soldered boards, so intermittent pin contact is common — and a bad read looks plausible while being complete garbage. The calculator independently verifies the calibration checksum and rejects a corrupt read before you pay.
Does this keep my car's own tune?
Yes. We patch your own calibration — exactly two things change: the VATS enable bit and the calibration checksum that protects it. Your fuel tables, spark tables, axle ratio, and every other setting are untouched, byte for byte.
What about the checksum?
It is corrected automatically. GM memcal calibrations carry an additive checksum over the calibration area; changing the VATS bit invalidates it, and an ECM that fails its checksum can refuse to run. The returned file has a recomputed, verified checksum and is ready to burn.
What chip do I burn it to, and how does it go in?
Burn the returned file to a blank 27C256 (AT27C256R one-time, or W27C257 if you want a re-writable chip). To install without soldering, use a Moates G1 memory adapter: the chip plugs into the G1, the G1 into your memcal, and the memcal back into the ECM. The G1 keeps the memcal's laser-etched resistor and knock packs, which cannot be duplicated.
The file came back saying my car has no VATS. What does that mean?
Some calibrations on these same ECMs never consult VATS at all — the enable bit is already clear and the VATS frequency window is zeroed. If that is your file, a VATS-OFF chip would change nothing, so we tell you and do not charge you. A no-start on that car is a PASS-Key or body-control problem, not the chip.
My chip will not read cleanly — what now?
Ship us the memcal. The mail-in GM VATS delete is $250 and we read it here on proper equipment, patch it, burn a new chip, and send it back ready to plug in. That is the right path when pins are corroded or the chip is damaged.
Is this legal?
This service is for diagnostics, repair, restoration, engine swaps, motorsport, and off-road use where legally permitted, on a vehicle you own or are authorized to service. We do not provide emissions defeat or delete files, and nothing here is intended to enable vehicle theft. You are responsible for lawful ownership and for compliance with all local, state, and federal law.
Ready to kill VATS?
Upload your 32 KB memcal read. We verify it free — you only pay if we can actually do it.