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GM Terms

See general terms.

Term Abbreviation Definition
Advanced Safety Control Module ASCM Car computer/module that does sensor fusion from Radar and Camera to create ACC and LKA messages to PCM (powertrain control module). Typically located in the trunk.
Calibration n/a Packaged adjustments to running parameters of firmware running on GM vehicles. Updates available from SPS within TIS2Web
Firmware n/a Base operating system for various devices throughout the vehicle. Updates available from SPS within TIS2Web
GDS2 Global Diagnostic System 2 GM system for advanced diagnostics and firmware flashing
GMLAN GM Local Area Network Single wire propriety interface present on the CAN connector in GM vehicles.
MDI Multiple Diagnostic Interface GM service device connecting the vehicle to a computer. Lower price generics exist such as vxdiag.
SPS Service Programming System Firmware and calibrations within the TIS2Web application. Updates can be seen for vehicles by VIN without cost here.
Tech2Win Tech2 for Windows Emulated legacy diagnostic interfaces for Windows. Runs in an emulated terminal.
TIS2Web Techline Information System ACDelco site providing diagnostics and firmware for cars on a subscription basis. Interacts with vehicle via GM MDI. Java webstart application.

Vehicle Requirements

The GM RPO code for CRUISE CONTROL AUTOMATIC, ADAPTIVE WITH STOP/GO is KSG. Most GM 2016-2020 vehicles with ACC, LKA can be supported.

Look for the smooth Chevy logo on the grill, which is transparent to radar. Car dealers will often reuse external photos, so don't trust them. The left panel of the steering wheel will have a central button to adjust follow distance.

Volt ASCM is the trunk, on the driver side, behind the storage cabinet:

Unofficial Vehicles

Any GM vehicle 2016+ with front camera and lane keeping. These will only control steering, not gas/brake. With a comma pedal, limited longitudinal control is possible by using Low gear to decelerate. To upstream these vehicles, find a CAN bus and command to control friction brakes!

For the Chevy Bolt, see the openpilot Bolt wiki.


First engage must be above 18 mph.

Minimum Speeds

All: Below 8 mph, LKA steering is unavailable.

2017: 18 mph longitudinal control, although 0 mph often works, but sometimes cruise faults.

2018+: 0 mph longitudinal control


2017: Auto-resumes from stop at 0mph.

2018+: Must press RESUME to resume from stop.



  1. comma three devkit w/ OBD-II car harness
  2. ASCM wiring harness

Other ASCM Harness Methods

Harness Examples

ASCM 14-pin stub

Camera stub

Connect switched +12V (e.g. ignition on, rearview mirror connector or driver fusebox) to pin 9 (radar power) of cam connector. This will turn on the front radar when the car is powered on.

Original instructions from Zoneos

Homemade OBD-II to OBD-C Harness

Map OBD-II to OBD-C female (at comma device) schematic

11 CAN2L A10 CAN1L
16 12V VBUS
B8 SBU2 1kΩ to GND

CAN Error, OBD-C Connector Orientation

ODB-C cable orientation matters. If you receive a CAN Error, flip the OBD-C connector orientation 180º either at the male-to-male adapter or at the OBD-II car port.

Troubleshooting Open Pilot's Cruise Fault Warning on Volt (Brake Pedal Positioning)

An issue where ACC brake-pressed is not the same as openpilot brake-pressed. This causes a cruise fault or controls mismatched warning when engaging, tapping the brakes, or hitting bumps.

The pedal failure is addressed by service bulletin for 2016-2017 Volt Brake Pedal Push Rod Retainer (part 39081933), TSB 16-NA-147. If using the top of your foot to pull up on the brake pedal resolves the fault, this is likely the cause.

GM dealerships may fix this fault for free - just make sure to remove the OBD-II splitter and put the ASCM toggle switch in dealer mode before taking the Volt in for service.

This condition is often mis-diagnosed by service centers - their first diagnostic step is usually to re-flash the front camera and/or radar sensor. Politely referencing TSB 16-NA-147 should help guide the service department on the right path.

Forks that Play Nice with GM Vehicles