The Mazda RX8 utilises a high-speed CAN bus for communicating between the various modules found throughout the vehicle, with each module constantly transmitting and receiving packets of data containing variables relevant to its operation. The following table contains a list of CAN bus messages that are required in the operation of the RX8s instrument cluster, each being of standard frame size and transmitted onto the bus at a speed of 500 kBit per second.
ID | Size (Bytes) | Module | Contents |
---|---|---|---|
0x420 | 7 | PCM | Coolant Temperature & Warning Lights |
0x201 | 8 | PCM | Vehicle Speed & Engine RPM |
0x650 | 1 | PCM | Cruise Control lights |
0x231 | 2 | TCM | Gear display, AT warning light |
0x300 | 1 | EPS | Power steering warning light |
0x212 | 6 | ABS/DSC | Brake warning light, DSC OFF light, DSC light, ABS light |
PCM - Powertrain Control Module
TCM - Transmission Control Module
EPS - Electronic Power Steering
ABS - Anti-lock Braking System
DSC - Dynamic Stability Control
Message 0x420 - Coolant Temperature & Warning Lights
Coolant Temperature & Warning Lights
This message, originating from the PCM, is responsible for initialising the cluster, allowing for the engine-related warning lights to be cleared and the engine coolant temperature to be displayed on the gauge. If the cluster doesn't receive this message at least once every couple of seconds, then all of the warning lights will default to being illuminated and the needles of the oil pressure/coolant temperature gauges will sit far to the left, off the face of the gauge itself.
Byte | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
---|---|---|---|---|---|---|---|---|
0 | Coolant Temperature | |||||||
1 | N/A | |||||||
2 | N/A | |||||||
3 | N/A | |||||||
4 | - | - | - | - | - | - | - | OilP |
5 | - | CEL |
- | - | - | - | - | - |
6 | OilL |
Batt |
- | - | - | ECL |
- | - |
Message 0x201 - Vehicle Speed & Engine RPM
Vehicle Speed & Engine RPM
This message, also originating from the PCB, broadcasts both the engine speed (RPM) and the vehicle speed, which is likely being fed to the PCM from
the sensor on the extension housing of the transmission. The values accepted by the cluster for the vehicle speed and RPM aren't 1:1, and require scaling
and sometimes an offset.
For example, the expected vehicle speed is in km/h, but with an offset value of 100.0 and a scale of 100.0
(kmh + 100.0) * 100.0
Byte | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
---|---|---|---|---|---|---|---|---|
0 | Engine RPM rpm * 3.85 |
|||||||
1 | ||||||||
2 | N/A | |||||||
3 | N/A | |||||||
4 | Vehicle Speed (km/h + 100.0) * 100.0 |
|||||||
5 | ||||||||
6 | N/A | |||||||
7 | N/A |
Message 0x650 - Cruise Control
Cruise Control
Once again originating from the PCM, this message simply sets the state of the Cruise Control status indicator lights
Byte | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
---|---|---|---|---|---|---|---|---|
0 | CCM |
CC |
- | - | - | - | - | - |
Message 0x231 - Shift Position Indicator
Shift Position Indicator
This message originates from the TCM and is used by the instrument cluster on automatic transmission models to display the current shifter position.
The gear position can be displayed in either regular or manual mode, selected by setting the Man
flag in byte 1. In regular mode, the cluster will
display P, R, N or D. In manual mode, it will display a numeric value on the 7-segement display representing the gear the transmission is currently in. For the
specifics of each mode, refer to the entry for the Man
flag in the flag descriptions table.
Byte | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
---|---|---|---|---|---|---|---|---|
0 | Manual Mode Gear First (1) to Sixth (6) |
Shifter Position P (1) | R (2) | N (3) | D (4) |
||||||
1 | Man |
AT |
- | - | - | - | - | - |
Message 0x300 - Electronic Power Steering
Electronic Power Steering
This message, originating from the EPS Control Module, sets the state of the EPS malfunction light.
Byte | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
---|---|---|---|---|---|---|---|---|
0 | EPS |
- | - | - | - | - | - | - |
Light | Flag | Name | Description |
---|---|---|---|
EPS |
Electronic Power Steering Malfunction Light | Illuminates the EPS malfunction light when set to 1 |
Message 0x212 - ABS, Traction Control and Stability Control
ABS, Traction Control and Stability Control
This message is broadcast by the ABS/DSC module, it is used to set the various malfunction indication lights relating to ABS/DSC/TCS.
It appears the warning light for the TCS can only be illuminated while the DSC OFF (DSC
) flag is set to 1. As I'm not familiar
with the RX8 and the operation of its TCS, and the owners manual only briefly glosses over the topic, I am unable to determine the significance of this.
Byte | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
---|---|---|---|---|---|---|---|---|
0 | N/A | |||||||
1 | N/A | |||||||
2 | N/A | |||||||
3 | - | - | - | - | - | DSC |
- | - |
4 | - | BSW |
- | - | ABS |
- | - | - |
5 | - | - | TCSA |
TCSO |
- | - | - | - |