Auto Repair Help
LANCE’S CORNER – AUTO REPAIR HELP

DIAGNOSE – ANTI-LOCK BRAKE LIGHT STAYS ON
AFTER ENGINE IS STARTED

by Lance Wright


SYMPTOM SUMMARY

The “ABS” or “Anti-Lock Brakes” light remains on after the engine is started and remains on or flashes.

USUAL CAUSEabs_light
The Anti-Lock brake system is designed to rapidly modulate the braking action during a panic stop. This prevents the wheels from locking up and maintains vehicle control and stability. An ABS control module monitors the wheel speed and other various sensors to determine when wheel lock-up is about to occur. The ABS module continually performs diagnostics to ensure that the system is functional. When a malfunction occurs, the ABS module will illuminate or flash the ABS or Anti-Lock light on the dash panel to alert the driver. During start up, the module will illuminate the light as a self test. Shortly after the engine is started, the light should go out indicating the system is functional. If the light remains on the ABS Module has detected a system failure. On most vehicles, the ABS system will not be functional while the light is illuminated. Usually, normal braking will result unless the failure is related to a component that is used for both normal braking and anti-lock braking. If the Red Brake light is also on, normal braking may be degraded as well indicating a system wide failure.

DIAGNOSIS
On almost all ABS systems the module will store a diagnostic trouble code that relates to the circuit or component that has failed. The diagnosis will require the module to be placed in self diagnostic mode, which will result in it transmitting the stored diagnostic code. Once the code is received, the diagnosis should focus on that particular component or sensor. A vehicle specific service manual will indicate how the module is placed into diagnostic mode and will indicated what circuit or component relates to what code. Often a special scan tool, similar to a hand held computer, is required to interface with the module.

CORRECTIVE ACTION
Once the code has been retreived from the modules memory, that component or circuit will require service. Some components, such as the wheel speed sensors, are usually simple to replace. However, other components such as the hydraulic modulator and control solenoids require special tools and special bleeding procedures to ensure proper operation.

PRECAUTIONS, TIPS, and NOTES
If the ABS light is on, the failure should be corrected as soon as possible. If possible, you should leave repairs to the ABS system to trained service personnel that are equipped with the correct tools and equipment. The Hydraulic Modulator may contain brake fluid pressurized to over 1,500 psi, that if not properly bled, can pose significant danger to someone servicing the system.


(Lance owned his own auto repair shop for 30 years before retiring in 2006.)

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13 Comments on "Antilock Brake Light Stays On After Engine Is Started"

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Sheila Swink
3 years 4 months ago

The light goes off right after starting, but then comes back on after the van moves.

3 years 1 month ago

I encountered the same problem before, I just leave it to my mechanic friend. You have to fix the issues immediately on your anti-lock breaks for safety.

John Durward
2 years 8 months ago

hi abs light is on but gear changing is not smooth in my Merc S-Class 350 Auto.

Thank you

ronnie
2 years 1 month ago

hi my ABS and traction light has started staying on recently had new brake pads fitted

hector
1 year 11 months ago

my 1988 f-350 havy duty 7.3 diesel engine keeps the rear ABS warning light on after start the engine could you help me please

Jo schmo
1 year 10 months ago

Screw the warning light. Take that POS Havy duty diesel to the scrap yard and have it crushed immediately.

casper lafata
1 year 2 months ago

my abs light sstays on everything else seeems tto be working working fine.

8 months 9 days ago

My vehicle volkswagen-golf III GTI,the ABS indicator light always stays on and it affects my break system,what shuld i do to solve the problems please,your advises is highly needed thanks

jewels
7 months 11 days ago

abs light came on and I could not brake, it acted as if I hit ice and I was just starting up leaving a parking lot..
Parked it and it was making a weird noise.. then waited .. started it back up and everything was fine.. what is this about.. scared to drive it and get stranded some where..
Just had my security wires fixed to read my key, could it be something the mechanic did?

5 months 13 days ago

my car give problem ABS,Esp,handbrake stay ON and it lock autometically after start the engine

4 months 27 days ago

My abs is vibrant why

Rafael
1 month 8 days ago

Hi my abs is on my 1997 BMW 528i

Carol
26 days 15 hours ago

Many times it is just a bad sensor. Easy fix.

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