Write VCM

Writing the VCM

There are a few different ways you can write to the VCM. They are:

"Write Calibration Only" is the regular, safest and fastest way to rewrite the VCM. ALWAYS use "Write VCM" when making regular tuning changes.

The "Write Entire" and "Write VIN/Tunerlock/VATS" options are special features to be used by advanced users only and are discussed further below.

Steps for Writing the VCM

  1. Plug the interface cable into the vehicle OBD2 port and PC serial/USB interface. See Connecting to the Vehicle section for more information.
  2. Open VCM Editor, ensure a valid file for this VCM are currently open (or have just been read) and select "Write Calibration Only" from the "Flash" menu. Alternatively, click the red "Write Calibration Only" icon on the toolbar. The Write VCM form will appear. (Advanced users may select the "Write Entire" or "Write VIN/Tunerlock/VATS" option).
  3. Put the key in the ignition and turn to the on position (do not start the vehicle).
  4. Make sure the doors are closed and accessories are turned off.
  5. Wait 10 to 15 seconds.
  6. Click the "Begin" button.
  7. Allow the PC to write the VCM until it displays "VCM Write Completed"
  8. Turn off ignition and optionally unplug the interface cable.
  9. The new calibration has now been written to the PCM.


VCM Recovery

When rewriting using the "Rewrite Entire VCM" or the "Rewrite VCM VIN and CAL" options, critical components of the VCM software must be erased and re-written. If the VCM loses power during writing of these critical system components, the VCM may become unrecoverable. Do not power down the VCM under any circumstances during a write failure using these advanced options.

Rewrite Entire (selected vehicles only)

This is a useful feature for the tuner shop or mail order tuner and doesn't apply much to a single vehicle tuner. What this can allow you to do is program a VCM that came from another vehicle for your specific vehicle type. You must make sure that the VCM hardware matches. This is a very powerful feature and must be used with caution. If you write a VCM with a file that doesn't belong on it, you could damage the VCM and cause it to be unrecoverable. It is not available on for all vehicle types.

Frequent Questions

When should I use "Write VCM" ?
All the time except in the circumstances described in the following sections.
Never use the following methods to recover a VCM that has failed during a normal Write VCM operation.

When should I use "Write Entire" ?
The only time you should use the Entire VCM Write feature is if you are updating the software on the VCM to a new operating system. For example, using a Corvette VCM with electronic throttle in a Firebird that has cable driven throttle body (same VCM hardware, different Operating System).
If you are recovering from a standard VCM Write failure, using the Rewrite Entire feature will not help ensure the recovery of your VCM. In fact, in a failure scenario from a standard VCM Write you are at more risk for total VCM loss when you try to recover using the Rewrite Entire.

When should I use "Rewrite VIN/Tunerlock/VATS" ?
The only times you would need to use this option is if you have updated the VIN of the VCM (via the editor), are relinking the VATS system or are applying the Tunerlock feature to lock or unlock the VCM. Generally these things only need to be done once (and can be done during a "Write Entire" as well).

Note: It is a good idea to try and limit the advanced writes (Entire and VIN/Tunerlock/VATS) to only once. ie. setup the new operating system with all required VIN, Tunerlock and VATS information and then choose "Write Entire" for the first write only. Then use the normal "Write Calibration Only" option for regular tuning.

"Write VCM" failed and now my car won't start, what do I do?
Don't panic. An error during the write process has occurred.
Follow these guidelines:

Write times

Approximate write times (error free, high speed mode) are as follows:

VCM Type Write Calibration Only Write Entire Write VIN/Tunerlock/VATS
LS1 V8 PCM (512k) 30 secs 2 mins 15 secs
LS1 V8 PCM (1024k) 30 secs 4 mins 15 secs
V6 PCM (512k) 30 secs 2 mins 15 secs
V6 PCM (1024k) 30 secs 4 mins 15 secs
LS2 V8 ECM (1280k) 20 secs 2 min 45 secs n/a
LS2 V8 ECM + TCM (1984k) 30 secs 3 min 50 secs n/a
Alloytec 30 secs 3 min 50 secs n/a
P12 I4/I5/I6 ECM 30 secs 2 min 45 secs n/a
E67 ECM + TCM n/a 3 min 50 secs n/a