Brake Assist Warning Light

[duncboyd]

I have a 2010 Astra SRI and the brake assist (BAS) has just starrted showing a warning

I haent found much information from googling.

Im hoping its a simple thing like the sensor on the brake servo[ATTACH=CONFIG]220[/ATTACH]

Any advice?

[tucpal]

rusty might assist with this one

[Rusty2009]

It's a very vague description,

But I would image the best thing would be to get it booked into a dealers for them to look at it, unless you know of someone close with an MDI or Vauxcom that check for any fault codes?

There is this

http://workshop-manuals.com/vauxhall/ast...diagnosis/

I would of thought it was linked into the ABS system a quick reset may clear the problem but it even if goes on a reset it may come back.

[Rusty2009]

[h=2]ABS Description and Operation[/h]This vehicle is equipped with a Continental Teves Mk60/Mk70 brake system. On vehicles without stability control, the electronic brake control module (EBCM) and the brake pressure modulator valve assembly are serviced separately. The brake pressure modulator valve assembly uses a 4 circuit configuration to control hydraulic pressure to each wheel independently.
The vehicle may be equipped with the following vehicle performance enhancement systems.

[TABLE]
[TR]
[TD] • [/TD]
[TD]Antilock brake system (ABS)[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Traction control[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Stability control[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Dynamic rear proportioning[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Hydraulic brake assist[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Hill start assist[/TD]
[/TR]
[/TABLE]

The following components are involved in the operation of the above systems:

[TABLE]
[TR]
[TD] • [/TD]
[TD]EBCM - The EBCM controls the system functions and detects failures. It supplies voltage to the solenoid valves and pump motor.[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Brake pressure modulator valve assembly - The brake pressure modulator valve assembly contains the following components: [/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] -- [/TD]
[TD]Hydraulic pump with pump motor[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] -- [/TD]
[TD]Four isolation vales[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] -- [/TD]
[TD]Four dump valves[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] -- [/TD]
[TD]Two traction control/stability control supply valves[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] -- [/TD]
[TD]Two traction control/stability control isolation valves[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] -- [/TD]
[TD]Pressure sensor[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] -- [/TD]
[TD]High pressure attenuators[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] -- [/TD]
[TD]Low pressure accumulator[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Multi-axis acceleration sensor - The yaw rate, lateral acceleration and longitudinal acceleration sensors are combined into one multi-axis acceleration sensor, external to the EBCM. The EBCM receives serial data message inputs from the yaw rate, lateral acceleration and longitudinal acceleration sensor and activates stability control and hill start assist function depending on multi-axis acceleration sensor input.[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Steering angle sensor - The EBCM receives serial data message inputs from the steering angle sensor. The steering angle sensor signal is used to calculate the desired yaw rate.[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Traction control switch - Traction control and stability control are manually disabled or enabled by pressing the traction control switch.[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Wheel speed sensors - The EBCM sends a 12 V reference voltage to each wheel speed sensor. As the wheel spins, the wheel speed sensor produces an alternating current square wave signal. The EBCM uses the frequency of the square wave signal to calculate the wheel speed.[/TD]
[/TR]
[/TABLE]

[h=3]ABS[/h]When wheel slip is detected during a brake application, an ABS event occurs. During ABS braking, hydraulic pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. A separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decrease, hold, or increase hydraulic pressure to each wheel. The ABS does not, however, increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking.
During ABS braking, a series of rapid pulsations is felt in the brake pedal. These pulsations are caused by the rapid changes in position of the individual solenoid valves as the EBCM responds to wheel speed sensor inputs and attempts to prevent wheel slip. These pedal pulsations are present only during ABS braking and stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping noise may also be heard as the solenoid valves cycle rapidly. During ABS braking on dry pavement, intermittent chirping noises may be heard as the tyres approach slipping. These noises and pedal pulsations are considered normal during ABS operation.
Vehicles equipped with ABS may be stopped by applying normal force to the brake pedal. Brake pedal operation during normal braking is no different than that of previous non ABS systems. Maintaining a constant force on the brake pedal provides the shortest stopping distance while maintaining vehicle stability. The typical ABS activation sequence is as follows.
[h=4]Pressure Hold[/h]The EBCM closes the isolation valve and keeps the dump valve closed in order to isolate the slipping wheel when wheel slip occurs. This holds the pressure steady on the brake so that the hydraulic pressure does not increase or decrease.
[h=4]Pressure Decrease[/h]If a pressure hold does not correct the wheel slip condition, a pressure decrease occurs. The EBCM decreases the pressure to individual wheels during deceleration when wheel slip occurs. The isolation valve is closed and the dump valve is opened. The excess fluid is stored in the accumulator until the pump can return the fluid to the master cylinder or fluid reservoir.
[h=4]Pressure Increase[/h]After the wheel slip is corrected, a pressure increase occurs. The EBCM increases the pressure to individual wheels during deceleration in order to reduce the speed of the wheel. The isolation valve is opened and the dump valve is closed. The increased pressure is delivered from the master cylinder.
[h=3]Traction Control[/h]When drive wheel slip is noted, the EBCM will enter traction control mode.
First, the EBCM requests the engine control module (ECM) to reduce the amount of torque to the drive wheels via a serial data message. The ECM reduces torque to the drive wheels and reports the amount of delivered torque.
If the engine torque reduction does not reduce drive wheel slip, the EBCM will actively apply the brakes on the slipping drive wheel. During traction control braking, hydraulic pressure in each drive wheel circuit is controlled to prevent the drive wheels from slipping. The EBCM commands the pump motor and appropriate solenoid valves ON and OFF to apply brake pressure to the slipping wheel.
Traction control can be manually disabled or enabled by pressing the traction control switch.
[h=3]Stability Control[/h]Stability control provides added stability during aggressive manoeuvres. Yaw rate is the rate of rotation about the vehicle's vertical axis. The stability control is activated when the EBCM determines that the desired yaw rate does not match the actual yaw rate as measured by the yaw rate sensor.
The desired yaw rate is calculated by the EBCM using the following inputs:

[TABLE]
[TR]
[TD] • [/TD]
[TD]Steering wheel position[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Vehicle speed[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Lateral acceleration[/TD]
[/TR]
[/TABLE]

The difference between the desired yaw rate and the actual yaw rate is the yaw rate error, which is a measurement of oversteer or understeer. When a yaw rate error is detected, the EBCM attempts to correct the vehicle's yaw motion by applying brake pressure to one or more of the wheels. The amount of brake pressure which is applied varies, depending on the correction required. The engine torque may be reduced also, if it is necessary to slow the vehicle while maintaining stability.
Stability control activations generally occur in turns during aggressive driving. When braking during stability control activation, the brake pedal may pulsate.
Stability control can be manually disabled or enabled by pressing the traction control switch for 5 s.
[h=3]Dynamic Rear Proportioning[/h]The dynamic rear proportioning is a control system that replaces the mechanical proportioning valve. Under certain driving conditions the EBCM will reduce the rear wheel brake pressure by commanding the appropriate solenoid valves ON and OFF.
[h=3]Hydraulic Brake Assist[/h]The hydraulic brake assist function is designed to support the driver in emergency braking situations.
The EBCM receives inputs from the brake pressure sensor. When the EBCM senses an emergency braking situation, the EBCM will actively increase the brake pressure to a specific maximum.
[h=3]Hill Start Assist[/h]The hill start assist allows the driver to launch his vehicle without a roll back while he is moving his foot from the brake pedal to the accelerator pedal. The EBCM calculates the brake pressure, which is needed to hold the vehicle on an incline and locks that pressure for a certain time by commanding the appropriate solenoid valves ON and OFF when the brake pedal is released. Hill start assist is activated when the EBCM determines that the driver wishes to move his vehicle up-hill, either backwards or forwards.
The following inputs are used for hill start assist feature:

[TABLE]
[TR]
[TD] • [/TD]
[TD]Brake switch[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Brake pressure[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Longitudinal acceleration[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Engine torque[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Reverse gear information[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Clutch switch[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Accelerator pedal position[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]Vehicle speed[/TD]
[/TR]
[/TABLE]

[h=3]Driver Information Indicators[/h][h=4]Brake Warning Indicator[/h]The instrument cluster turns the brake warning indicator ON when the following occurs:

[TABLE]
[TR]
[TD] • [/TD]
[TD]The instrument cluster performs the bulb check. [/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]The EBCM detects a fault and sends a serial data message to the instrument cluster requesting illumination.[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]The body control module (BCM) detects that the park brake is engaged. The instrument cluster receives a serial data message from the BCM requesting illumination. [/TD]
[/TR]
[/TABLE]

[h=4]ABS Indicator[/h]The instrument cluster turns the ABS indicator ON when the following occurs:

[TABLE]
[TR]
[TD] • [/TD]
[TD]The instrument cluster performs the bulb check. [/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]The EBCM detects a malfunction which disables the ABS and sends a serial data message to the instrument cluster requesting illumination.[/TD]
[/TR]
[/TABLE]

[h=4]Traction Control/Stability Control Active Indicator[/h]The instrument cluster turns the traction control/stability control-active indicator ON when the following occurs:

[TABLE]
[TR]
[TD] • [/TD]
[TD]The instrument cluster performs the bulb check. [/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]The ABS system is in traction control or stability control mode.[/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]The EBCM detects a malfunction which disables the traction control or stability control and sends a serial data message to the instrument cluster requesting illumination.[/TD]
[/TR]
[/TABLE]

[h=4]Stability Control Off Indicator[/h]The instrument cluster turns the stability control off indicator ON when the following occurs:

[TABLE]
[TR]
[TD] • [/TD]
[TD]The instrument cluster performs the bulb check. [/TD]
[/TR]
[/TABLE]

[TABLE]
[TR]
[TD] • [/TD]
[TD]The driver manually disables the stability control by pressing the traction control switch. The EBCM sends a serial data message to the instrument cluster requesting illumination.[/TD]
[/TR]
[/TABLE]

[duncboyd]

Hi Rusty,

Thanks for the details, dont see what I need there though. Here are some more details:

As I understand it the BAS system works by sensing the rate at which the break pedal is pressed and then takes over if it thinks the driver is trying to emergency stop. (youtube "brake assist system")

The item in the picture is some sort of pressure sensor and is the only sensor on the servo so im specuating this could be the problem.

Disconnecting the battery for a while doesnt clear the error. It comes up right away when the ignition is on, engine doesnt need to be running.

Disconnecting the cable from the sensor doesnt raise any other errors which is encouraging.

If any of you guys can confirm that this sensor is part of the BAS system that would help me on my way.

Anyone who is keen could unplug the cable (easy) from the sensor and see what error appears on the dash ("service brake assist"?). Maybe then have to disconnect the battery for a while to clear the error though so that might put folks off.

Cheers,

[Rusty2009]

I'll have a look again, where are you based mate?


Sent from my iPhone 5c using Tapatalk.

[Rusty2009]

Hydraulic Brake Assist


The hydraulic brake assist function is designed to support the driver in emergency braking situations.
The EBCM receives inputs from the brake pressure sensor. When the EBCM senses an emergency braking situation, the EBCM will actively increase the brake pressure to a specific maximum.

I've found Schematics for you I doubt it will be much help.

Hydraulic Brake Schematics

Where is this sensor you are talking about?

[duncboyd]

Thanks for the details. Im in West Lothain Scotland

Electronics is my subject so I can follow the schematic ok but it doesnt help much as you suspected.

The item in the picture does appear to be a break pressure sensor, not a switch as in the schmatic. It gets 5v and a digital line.

The connector comes off easy enough just by squeesing the gray connector and pulling it out.

[ATTACH=CONFIG]221[/ATTACH]

[Rusty2009]

A bit too far from me then,

I shall have a look over the weekend and see what happens when I disconnect it.