Overview
The instrument cluster is a self-contained module in the dash featuring the speedometer, tachometer, fuel gauge, temperature gauge and usually a trip computer retaining information such as the odometer.
VT/VX/VY/VZ Commodores
Unlock Procedure
Before any configuration data can be read or written, the cluster must be in an "unlocked" state. This is achieved using a challenge-response authentication mechanism (also known as a seed/key pair). A seed can be requested from the cluster by issuing a Mode 11 request, followed by table number 00. The cluster will respond with Mode 11 and two bytes that form the seed. The key value is calculated and sent as a write to table 01 in Mode 11. For details on calculating key values, see GM Seed/Key. The tables below illustrate the unlocking procedure.
Seed request
| Length (bytes) | Field | Value | Notes |
|---|---|---|---|
| 1 | ID | F2 |
|
| 1 | Length | 57 |
|
| 1 | Mode | 11 |
|
| 1 | Table | 00 |
|
| 1 | Checksum | A6 |
Seed response
| Length (bytes) | Field | Value | Notes |
|---|---|---|---|
| 1 | ID | F2 |
|
| 1 | Length | 59 |
|
| 1 | Mode | 11 |
|
| 2 | Seed | S | 16-bit Seed Value |
| 1 | Checksum | c |
Key transmission
| Length (bytes) | Field | Value | Notes |
|---|---|---|---|
| 1 | ID | F2 |
|
| 1 | Length | 59 |
|
| 1 | Mode | 11 |
|
| 1 | Table | 01 |
|
| 2 | Key | K | 16-bit Key Value |
| 1 | Checksum | c |
Key response
| Length (bytes) | Field | Value | Notes |
|---|---|---|---|
| 1 | ID | F2 |
|
| 1 | Length | 58 |
|
| 1 | Mode | 11 |
|
| 2 | Status | Equals key K on successful unlock, FFFF on failure.
| |
| 1 | Checksum | F8 |
Configuration Tables
| Table | Length | Type | Description |
|---|---|---|---|
01 |
2 |
u16 |
Speedometer Pulses (u16) |
50 |
1 |
Boolean | Police Mode |
67 |
1 |
Boolean | Show Distance To Go |
69 |
1 |
Boolean | Show radio status |
6D |
1 |
Boolean | Stopwatch |
7E |
1 |
Boolean | Automatic Transmission |