My ABS/brake light has illuminated without apparent cause and now my odometer
and speedometer are not functioning correctly. What steps should I take next?
Your mechanic will start by using a bi-directional scanner to see which error codes
have come up on the dashboard and identify potential components causing warning
lights and speedometer malfunction. This can help them narrow down which parts
may be responsible.
1. Faulty ABS Sensor
Modern cars use ABS sensors to monitor each wheel’s speed. In addition, traction
control systems use them to restrict engine power from reaching specific wheels in
order to reduce slippage during acceleration on slippery surfaces. A defective sensor
may cause one of these systems to fail, potentially leading to loss of vehicle control
and leading to a loss of control of your vehicle.
Faulty ABS sensors may prevent your speedometer from functioning as intended,
making the speedometer inaccurate and nonfunctional. An easy way to test this is to
connect a multimeter to the ABS wiring harness at its sensor location and check for
voltage readings; if none are present then most likely your ABS sensor needs
replacing immediately.
Plug a diagnostic scanner into the OBD-II connector under your dash for use as well.
This will display any fault codes stored within your ABS module as well as error
codes pertaining to sensors.
2. Faulty ABS Module
Modern cars typically display an ABS warning light to indicate any problems with its
module; in older vehicles this might appear as a check engine light.
If your ABS light is illuminated, it is wise to have it evaluated by a professional as
soon as possible. Depending on the make and model of your car, ABS modules may
be very costly.
The ABS module relies on sensors to track each wheel’s speed and send signals
when one approaches locking up. If any of these sensors become defective, erratic
brake behavior and even interference with speedometer function could ensue.
Faulty sensors may be due to corrosion, electrical issues or software glitches; an
experienced mechanic should be able to quickly assess and address them cost-effectively.
3. Faulty Wiring
Sometimes wires or electrical connecters become exposed in the environment,
shorting it and blowing a fuse. This may also happen with ABS modules; when this
happens, an instrument cluster light may illuminate to indicate wiring issues.
The instrument cluster contains a sensor that monitors vehicle speed. If this sensor
becomes damaged or clogged with dirt, its reading may become inaccurate and
cause issues with both your computer and other gauges.
Your mechanic can use a bi-directional scanner to monitor error codes that have
been triggered, helping them pinpoint the right solution for your vehicle. A
technician may need to replace sensors; costs will range between $100 and $400
depending on vehicle model and location.
4. Faulty ECM
When your vehicle’s computer begins acting oddly and your speedometer stops
working, this could be an indicator of an ECM malfunction. This module controls
engine timing and fuel settings so if its failure significantly reduces performance.
Since symptoms usually come and go without any specific pattern or progression,
it’s wise to seek professional help immediately – it could save lives.
Your mechanic will begin by connecting a scanner to your onboard diagnostic (OBD)
port and monitoring what error codes appear. They may also use special ABS fault
code readers to help pinpoint the source of the issue. If ECM malfunction is the
cause, your mechanic will replace it, or possibly repair any sensors or wiring damage
with minimal time invested.
5. Faulty Engine Control Module
The Engine Control Module, or ECM, oversees many parts of a vehicle including ABS,
cruise controls and the speedometer. Unfortunately, its wiring between speed sensor
in transmission or differential to computer and instrument cluster can sometimes
become damaged and prevent proper signal transmission.
When this occurs, it can lead to various problems for the vehicle; one common
symptom being the illumination of the brake light. Usually this indicates an issue
with ABS sensors; however, it could also signal ECM troubles; professional diagnosis
with a diagnostic scanner will likely be required in order to identify which problem
exists – although repair costs should remain affordable.