I have a 2008 HINO 258 flatbed tow truck. The ABS light has been on since I got it. When I push the self test button for the ABS diagnostics, the light blinks 3 times, pauses, then blinks 4 times, pauses for a long period, then starts over with the same 3 and 4. I OHMd all the wheel speed sensors and they test normal, also cleaned them all and reinstalled them. This didnt change a thing. Disconnected the battery overnight and still didnt change a thing. The ABS light persistently stayed on for weeks after that. However, this week it started doing something different. In the morning once i leave and start moving down the road, the ABS light will turn off, but once i get off the throttle or hit the brakes the light comes back on, and will remain on. But if I turn the truck off, restart, then start moving again it will do the same and turn off until slowing down in some way. Every time I restart the truck now matter how many times in a row it will repeat this process. Im trying to find out if anyone out there has the same problems and knows what the cause is before i pony up a ton of dough and take it to the dealer. Even just some information on common failure items in the ABS system or anything that might help me get to the bottom of it. Its very important to me to get fixed as the light being on kills overdrive, causes the engine brake to come on and off at will which makes it aweful hard to operate my bed and wheel lift when it holds the RPM below idle with the PTO on, and also messes with the cruise control. ANY information would be greatly appreciated. BTW my truck has hydraulic brakes on it.
Good morning my name is XXXXX XXX I will try to help. Do you know what brand the ABS is? The codes sound like they are for a MeritorWabco system. There should be a tag on the unit with the manufacturer. MeritorWabco started using their E version in '06. It would be frame mounted and have the ecu on one end and a motor on the other. Please reply to me with this information so I can assist you.
The unit is a Wabco and it is mounted on the inner framerail rear of the cab
The 3-4 code means there is an issue with the right rear sensor.
To trouble shoot it check the resistance at the wheel end it should be between 900- 2000 ohms. Usually they are around 1300 ohms. If the resistance is good there you have to go to the harness at the ecu and check the resistance between pins 22 & 27 for the right rear. The resistance should be almost the same. If it's open or out of range there is an issue with the harness. If it's the same you have an ECU issue.
You should also check the AC out put at the wheel end. Put your multimeter on the AC scale and spin the wheel while the probes are in the connector. You should have at least .2 volts when you spin the wheel at 30 RPM. If you don't the sensor is out of adjustment. To adjust push the sensor in until it touches the tooth wheel, don't backt it off.
Attached is the pin out for the ECU connector.
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