Truck News


Keeping the light off

DON MILLS, Ont. - Lighting the antilock braking system (ABS) warning light has occupied a great deal of the trucking industry's collective gray matter over the past few years.But once the light comes ...

DON MILLS, Ont. – Lighting the antilock braking system (ABS) warning light has occupied a great deal of the trucking industry’s collective gray matter over the past few years.

But once the light comes on, how do you shut the darn thing off?

An ABS system consists of four basic components – an electronic control unit (ECU), wheel speed sensors, modulators, and wiring – all of which are ripe with areas that can experience a light-triggering fault. The key is identifying the problem quickly in order to get the unit back in service.

Often you need look no further than the light and its wiring to divine the defect.

During the power-up sequence, the light will flash on for roughly 2.5 seconds.

Drivers unfamiliar with ABS sometimes panic thinking something is wrong with their brakes at this point, but it’s just a matter of getting used to the system.

The warning light itself is a high side driver, so the lamp sends out 12 volts DC (vDC) that has to find its own ground. That contact is only a simple connection and is a prime spot for corrosion and tampering.

In addition, there can be compatibility issues when switching between incandescent and LED bulbs.

If these issues are ruled out, move to the next level of investigating.

If the light is flashing on and off every now and again, only when the truck is rolling, this is a sure sign of an intermittent problem.

These need to be addressed despite the fact the system is currently able to fix it – for the short-term – on its own.

This on-again, off-again situation will deteriorate and the problem will likely cost more money to fix in the long run.

Areas to check include fuses and circuits and any encroaching corrosion. Measuring the voltage under load should not yield a drop of more than 1.0 vDC.

If it does the fix may be as easy as greasing the connections – check with the manufacturer and be sure to heed their advice.

These relatively small problems can plague a fleet over time. In fact, more complex issues can be easier to identify … it’s simply a matter of looking up the fault code in the manual and taking the appropriate corrective action. n

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