4 replies to this topic

[BG11XV]

hey everyone 

 

got myself a new car/project 

 

been told the g3 impreza is canbus but i cant find any info at all 

 

coming from 12 years of 96 outback im kinda fresh to canbus stuff 

 

 

anyone know how to find out or somewhere i can call that will know 

 

 

 

cheers 

[Barbbachello]

Yes it will be

[BG11XV]

Yes it will be

Does that mean changing interior bulbs and headlights would be hard . I was going to get the black rs or wrx lights and change the interior bulbs to led

[RX25SE]

This is something I hear about quite a bit...... 

 

I think there needs to be some clarification about what CANBUS really is, and how control modules monitor circuits.

 

 

CANBUS

 

It it a Controller Area Network BUS. Its just the way individual control modules in the vehicle 'talk' to each other. There may be different types of networks in a single vehicle and the network used will depend on the amount and speed that the data needs to be transferred.

Body control (HVAC, lighting etc) doesn't require a large amount of data to make the heater fan change speed or the lights turn on (as the data may just be the state of a switch) so the network may a single wire 33.3KB/s BUS that uses a 5V differential, 5v being binary 0 and 0v being binary 1.

Engine/drive-train management would use a two wire BUS (one 'high side' and one 'low side' wire) that can  transfer data at 500KB/s and uses a 2v differential. When both wires are at 2.5v there is no voltage difference between the two wires so this 0v state represents binary 1. When the 'high side' goes up by 1v to 3.5v , the 'low side' also moves down by 1v to 1.5v, this creates a difference of 2v so the difference between the two wires is now 2v which represents binary 0.

 

The modules interpret the 1s and 0s as data, much like a barcode. This allows sensor data to be collected by one control module and shared on the 'network' for another module to 'read'. eg. The ABS module collects data from the wheel speed sensors as they are wired to that module, the ABS module places this data on the high speed BUS and the transmission control module reads the speed data and uses it to calculate gear shift points. The speed data may also be read by the Body Control module to lock the doors when a set speed is reached or to dip the headlamps from high beam if the car slows past a set speed.

 

CANBUS may also used by a scan tool to read diagnostic information from the vehicle. As all vehicles in Australia from 2006 use the standardised 'OBDII' (we actually use EOBD) protocol for emission monitoring, one of the standards is that the vehicle uses as specific set of CANBUS protocols for the vehicle to communicate diagnostic info to the scan tool. You may notice that all post 2006 cars have the same 16 pin OBD (Data Link Connector) and they all have pins 6 &14 populated, pin 6 being the 'high side' of the BUS and pin 14 being the 'low side' of the CANBUS. They also will have pins 4&5 as an earth and pin 16 as B+ to power the scan tool. They may have other pins populated for the scan tool to communicate with other networks, but it's not required for OBDII. Pre 2006 that use this 16 pin DLC cars may or may not be OBDII (VS Commodore uses this DLC but has no networks at all).

 

 

 

 

Circuit monitors

 

When a light is turned on in a modern car, it's usually done by a control module responding to an input signal. When the driver moves the headlamp switch to the 'on' position, the Body Control Module 'sees' the state of the switch change and responds by closing a 'driver' on the headlamp circuit; this completes the circuit, current flows and the headlamp illuminates. The driver is a transistor, basically and electronic switch.

The driver will have a small  'bias voltage' applied across it so the control module can monitor the state of the driver. When a globe is fitted to the circuit, the bias voltage is lost to ground through the filament of the globe (this could also be a relay coil if the module is driving a relay) so the control unit knows the globe an circuit are intact. If the module detects the bias voltage, a fault code is logged and the driver notified by a dashboard message. (some cars may only log a code, other only a message or maybe both).

 

When LED globes, or globes of incorrect wattage are fitted, the current in the circuit alters (due to the changed resistance - ohms law) so this changes the voltage drop across the closed driver. The module 'sees' the voltage drop move outside a preset value and reports the fault as above.

 

LED globes are essentially a diode so they behave the same way as a diode allowing current flow in one direction only. This is why they won't work if they are connected 'back to front' (polarity sensitive). As they have very high resistance, they draw very little current. If they are fitted where the circuit 'dims' the globe gradually (interior light) this can play havoc with the PWM (Pulse Width Modulation) control circuit in the module and may damage it. Often the LED will dim quickly before turning off.

 

Fitting LED interior lights to Subaru's has been known to cause the lamp control module to fail.

 

 

 

 

 

 

 

 

 

So CANBUS is really only about transferring data and has nothing to do with fault codes that occur after fitting different globes to OEM spec. 

 

 

 

 

I get REALLY FRUSTRATED when I see eBay ads that state their globes are 'CANBUS' compatible..........

[BG11XV]

This is something I hear about quite a bit...... 

 

I think there needs to be some clarification about what CANBUS really is, and how control modules monitor circuits.

 

 

CANBUS

 

It it a Controller Area Network BUS. Its just the way individual control modules in the vehicle 'talk' to each other. There may be different types of networks in a single vehicle and the network used will depend on the amount and speed that the data needs to be transferred.

Body control (HVAC, lighting etc) doesn't require a large amount of data to make the heater fan change speed or the lights turn on (as the data may just be the state of a switch) so the network may a single wire 33.3KB/s BUS that uses a 5V differential, 5v being binary 0 and 0v being binary 1.

Engine/drive-train management would use a two wire BUS (one 'high side' and one 'low side' wire) that can  transfer data at 500KB/s and uses a 2v differential. When both wires are at 2.5v there is no voltage difference between the two wires so this 0v state represents binary 1. When the 'high side' goes up by 1v to 3.5v , the 'low side' also moves down by 1v to 1.5v, this creates a difference of 2v so the difference between the two wires is now 2v which represents binary 0.

 

The modules interpret the 1s and 0s as data, much like a barcode. This allows sensor data to be collected by one control module and shared on the 'network' for another module to 'read'. eg. The ABS module collects data from the wheel speed sensors as they are wired to that module, the ABS module places this data on the high speed BUS and the transmission control module reads the speed data and uses it to calculate gear shift points. The speed data may also be read by the Body Control module to lock the doors when a set speed is reached or to dip the headlamps from high beam if the car slows past a set speed.

 

CANBUS may also used by a scan tool to read diagnostic information from the vehicle. As all vehicles in Australia from 2006 use the standardised 'OBDII' (we actually use EOBD) protocol for emission monitoring, one of the standards is that the vehicle uses as specific set of CANBUS protocols for the vehicle to communicate diagnostic info to the scan tool. You may notice that all post 2006 cars have the same 16 pin OBD (Data Link Connector) and they all have pins 6 &14 populated, pin 6 being the 'high side' of the BUS and pin 14 being the 'low side' of the CANBUS. They also will have pins 4&5 as an earth and pin 16 as B+ to power the scan tool. They may have other pins populated for the scan tool to communicate with other networks, but it's not required for OBDII. Pre 2006 that use this 16 pin DLC cars may or may not be OBDII (VS Commodore uses this DLC but has no networks at all).

 

 

 

 

Circuit monitors

 

When a light is turned on in a modern car, it's usually done by a control module responding to an input signal. When the driver moves the headlamp switch to the 'on' position, the Body Control Module 'sees' the state of the switch change and responds by closing a 'driver' on the headlamp circuit; this completes the circuit, current flows and the headlamp illuminates. The driver is a transistor, basically and electronic switch.

The driver will have a small  'bias voltage' applied across it so the control module can monitor the state of the driver. When a globe is fitted to the circuit, the bias voltage is lost to ground through the filament of the globe (this could also be a relay coil if the module is driving a relay) so the control unit knows the globe an circuit are intact. If the module detects the bias voltage, a fault code is logged and the driver notified by a dashboard message. (some cars may only log a code, other only a message or maybe both).

 

When LED globes, or globes of incorrect wattage are fitted, the current in the circuit alters (due to the changed resistance - ohms law) so this changes the voltage drop across the closed driver. The module 'sees' the voltage drop move outside a preset value and reports the fault as above.

 

LED globes are essentially a diode so they behave the same way as a diode allowing current flow in one direction only. This is why they won't work if they are connected 'back to front' (polarity sensitive). As they have very high resistance, they draw very little current. If they are fitted where the circuit 'dims' the globe gradually (interior light) this can play havoc with the PWM (Pulse Width Modulation) control circuit in the module and may damage it. Often the LED will dim quickly before turning off.

 

Fitting LED interior lights to Subaru's has been known to cause the lamp control module to fail.

 

 

 

 

 

 

 

 

 

So CANBUS is really only about transferring data and has nothing to do with fault codes that occur after fitting different globes to OEM spec. 

 

 

 

 

I get REALLY FRUSTRATED when I see eBay ads that state their globes are 'CANBUS' compatible..........

MATE !! THANKS SOO MUCH THAT WAS AN AWSOME READ ,, THANKS HEAPS