ABS Diagnostics and Maintenance
Some tips to help diagnose ABS issues. I have seen that many times the ABS issue is misdiagnosed. Roughly 80% of ECU’s returned to the manufacturer for warranty issues were misdiagnosed. There wasn’t anything wrong with the ECU. Technicians will tend to swap out parts until the fault goes away.
Lite-Check developed a 3 step check for ABS. First, turn on AUX power and watch the ABS lamp and listen for the clicking of the self test. Second, turn on the brake circuit to ensure the secondary power is getting to the ECU. The same self test will be performed. Final step is to start reading the ABS ECU. With Lite-Check’s Inspector 920, it is one button and the Inspector 920 will automatically identify the ECU. Then give the technicians all the information about the ECU on the trailer.
Many times it is a simple power issue getting to the ECU. I had the chance to help diagnose an ABS issue on a tanker with two ECU’s on it. Both ABS lights were staying on.
We used Lite-Check’s Inspector 920 to read the ABS ECU. We cleared out the faults and the lights went out. When we hooked the tractor up to the trailer, both ABS lights still stayed on. We hooked the tractor up to the Inspector 920 and turned the key on. The AUX pin was fluctuating in voltage from 3 VDC to 12VDC. The ABS system wasn’t getting constant power. The technician opened the junction box on the tractor and 2 cups of water poured out. There was corrosion on all the wiring and the tech found the actual cause for the ABS issue.
In this case, the tech shared with us that he would have been chasing the issue for hours. With out the Inspector 920, he would have swapped out all the parts, including both ECU’s.
Checking the power input, tech’s should ensure the correct voltage is getting to the ECU. They need a minimum of 9.5VDC to operate correctly. If there is corrosion, or any added resistance to the circuit, it can affect the voltage getting to the ECU.
While doing the trailer inspection, turn the AUX on to see the ABS light operation. If the light stays on there is a fault. The proper operation should be the ABS light comes on for 2 or 3 seconds, then goes off. During that time, there should be a clicking, valves firing, as part of the self test. If air is applied to the trailer at the time it will be an quick puff.
I hope this helps you and your technicians. The three step process can help troubleshoot ABS systems quickly. Using advanced diagnostics can help your technicians know exactly what is going on with the ABS system. The more they know, the more accurate the diagnosis is and reduces swapping out parts.