How do I defeat or bypass the third-gen VATS/Pass-Key system during an LS swap (keeping or removing the stock ECM)?
- VATS (Vehicle Anti-Theft System) is GM's umbrella term for its factory anti-theft families: PASS-Key I/II/III (key-based systems) and Passlock (lock-cylinder sensor systems), all of which gate engine start/running through the PCM.
- The original PASS-Key system is passively activated (no operator action beyond removing the key) and consists of an ignition key, an ignition lock cylinder, and a decoder module. (applies to pre-1997)
- PASS-Key III uses a transponder embedded in the key head energized by a coil around the lock cylinder, with over four trillion possible unique key codes. (applies to 1997+)
- In PASS-Key III, a valid key makes the decoder send an encoded message to the PCM enabling fuel flow and starter operation; an invalid key makes it send a different password that disables both fuel and starter. (applies to 1997+)
- PASS-Key III cannot be defeated by removing and reapplying vehicle power, and replacing the decoder module will not defeat it because of its decoder module password. (applies to 1997+)
- PASS-Key III performs a five-second security-light bulb check at key-on, which goes off for a valid key; an invalid key turns the security light on, and a fault detected during normal operation also enables the light. (applies to 1997+)
- Passlock I and II are key-based, fuel-shutdown anti-theft systems requiring the key cylinder to be mechanically turned with a key: the Passlock I R-Code goes to the instrument panel cluster (IPC), while Passlock II sends it directly to the BCM, which houses the decoder.
- Per Cardone, the Passlock lock cylinder contains a stationary Hall-effect sensor and a rotating magnet; turning the key creates a coded signal sent to the IPC or BCM, which then messages the PCM over serial data that the vehicle may be started.
- A fuel-enable bypass module only enables the fuel injectors; it does not defeat the starter interrupt, so the crank-disable relay must also be bypassed (jumper or rewiring), and the security light may stay on.
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Confirm against the instructions for your exact parts before wiring. More: VATS / anti-theft in our tuning guide.
How you handle VATS depends on whether the stock ECM stays. The VATS decoder module sits behind the dash on the HVAC plenum, above and left of the radio, and you have to remove the dash to reach it. It reads the resistor pellet in the key and controls both the starter relay and the stock ECM's injector enable. If you keep the stock ECM, permanently install a resistor that matches your key pellet in the resistor sensing circuit. If the stock ECM comes out, either bypass the control side of the start relay so the ignition switch drives it directly, or remove the start relay and wire the starter solenoid straight to the ignition switch. That relay exists only for the anti-theft function. On an LS swap where the new PCM also has VATS, turn VATS off in the LS PCM tune and bypass the car's VATS hardware.
Check this first:
- The resistance value of your key pellet if you're keeping the stock ECM
- Wire colors against the service manual for your year, since they vary
- That the new PCM's tune has VATS turned off
Careful: Make sure the starter circuit only engages in START and through the neutral/clutch safety switch, so the engine can't crank unexpectedly.
Based on what we've seen work across our own builds, our friends' builds and the wider LS community, reviewed by our lead shop tuner (over 20 years of LS and LT tuning experience). Every combination is different, so use at your own risk and check our safe tuning limits before any wide-open pass.
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Every option we know of
| Maker / product | Part # | Fits | Price | Where | Status / notes |
|---|---|---|---|---|---|
| the12volt.com VATS bypass diagram + value chart | n/a | GM VATS/Passkey systems | Free | the12volt.com install bay | Online Must match one of the 15 values |
| Generic Resistor assortment | n/a | Matching the measured pellet value | A few dollars | parts/electronics stores | Current production Get close to the chart value |
| Mail-order tuners VATS-delete tune | n/a | Stock GM PCMs | about $100-200 | various | Ongoing services No resistor needed |
Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.