I’ve been having issues with parasitic drain, found the source of the drain to be something in the ABS system (diagnosed by connecting a multimeter to the negative battery terminal and connector, and unplugging fuses until the ~100mA drain went down to zero). The main culprit was the ABS motor fuse (this made sense, because the ABS light had recently turned on).
To get a sense for where to start, I had the ABS codes scanned. Initially we got back two codes: 15-1 Right Rear Wheel Speed Sensor Open Circuit, and 54-1 Fail Safe Relay Failure. However, we turned the car off and on again, and the relay failure code went away, while the sensor open circuit code remained.
Based on this, I suspected the sensor had failed, so I first measured the resistance to check whether there is an open circuit in the sensor. However, the resistance reading across the last connector before the sensor was ~1.5kOhm, which from what I’ve found on the internet is the normal operating resistance.
This tells me that the sensor is probably fine, and the problem happens somewhere in the circuit before the connection I checked. Youtube served me well up until this point, but I’m having a lot of trouble figuring out what things to check next. I’d like to try measuring the resistance across that sensor circuit coming out of the ABS control module, but I can’t find any videos or instructions for safely trouble shooting that connector, or even a pin map for the cable going into the connector. Any help would be much appreciated!
Can you replace that relay and see what happens? There may even be an identical one and you could switch them and see if the problem moves with the relay.
Well, I really can’t find any information on where to find the ABS relay for this model. There’s no ABS relay in the fuse box, only a 40A fuse for the ABS pump motor.
Suggest to sus out the sensor problem first, as fixing it may solve the relay code. Faulty wheel speed sensors are a common problem reported here. Those sensors are just a coil of wire bolted to the chassis in close proximity to a magnet in the wheel hub that moves past the sensor, creating a voltage pulse each time it passes.
Look at the part on the hub that moves past the sensor as the wheel turns. Does it have any chipped or damaged teeth? Measure the gap b/t the sensor and the teeth. specs are 0.4 - 1 mm for front wheels, 0.2 - 1 mm rear.
I’m sort of surprised the sensor’s resistance spec is 1.5 k-ohm – it’s just a long coil of thin wire — , but I don’t see anything in the service data what it is supposed to be either, so maybe that’s correct, don’t know. (Just double checked and apparently that is correct for passive wss’s) The way this sort of thing is diagnosed by a shop is they inspect the signal coming from the sensor as they hand-rotate the wheel. They’re looking for a sequence of voltage pulses which increase in frequency the faster the wheel is turning. The Honda oem scan tool can probably do this, or if not the shop will use a laboratory o’scope. If everything seems to be ok otherwise, you could take it to a shop for this test, or just replace the sensor on a flyer and see if it helps or not.
It is sort of odd this problem results in a battery drain. If it is only 100 mA drain, that could be something as simple as the warning light on the dash. Is that warning light remaining on overnight?
I have an oscilloscope I could use to test this, so I will try that to completely rule out the sensor (given that the resistance is ok). Would a multimeter be sufficient for this test as well? As long as the wheel rotation is a bit slower than the multimeter refresh rate?
Good question re. the warning light. I’ve been unhooking the battery overnight to prevent drain, but I will keep it hooked up to see if the light stays on.
If you don’t mind sharing, where are you finding service data for this make and model… I am having an incredibly hard time finding detailed wiring diagrams and information about the ABS systems)
The abs code will not cause a battery draw you have 2 different problems.
you can only really test a abs sensor by using a graphing volt meter or oscilloscope. As you have to verify the sensor output when turning the wheel. Many times you have to look at a good corner then look at the bad one.
Not sure if you can view the speed sensor readings on live data from obd port. Unfortunately may require a expensive scan tool.
As for the draw have you verify that battery and charging system are working correctly.
Only thing I can suggest is to disconnect the abs module at the closed connector. And verify the draw is gone
And if so you module is defective.
I believe this to be true. Not sure on your model, but I think this is a passive abs sensor that has the tone wheel pick up in the wheel bearing. You can test it with a voltmeter in D.C. current. I struggled with this issue. Sensor responded at wheel sensor and at other side of connector but not at module. So I thought it was wiring between connector and module. I replaced the wiring and still had no readings at module. A jiggle test revealed it was the connector sporadically failing. All this to say, be sure to check out the connector carefully. When you do a parasitic drain test be sure to let the meter set for at least 15 minutes with no interruptions to let all modules shut down.
I posted about the draw in another post, the battery is brand new, as is the alternator (and voltage across the battery is good when engine is running, which probably rules out the alternator, from what I understand). Battery tests are also good. Draw is gone when I unplug the fuse for the ABS pump motor (goes to control module I believe). The draw is also a stable 72mA after waiting 30 min.
I should have tested whether unplugging the ABS control module connector would remove the drain. I was poking around yesterday and noticed that there was a large amount of oil/moisture inside the connector around the male pins, as well as corrosion on the female pins in the wire harness. I tried to dry it out as much as possible, but the drain was still present after cleaning them and plugging back in. Could be that the moisture caused a short somewhere in the ABS module… I’ll defo try to test whether unplugging removes the drain.
I found that info using AllData, a computer data base service. You can get AllData for yourself for just the one car, isn’t overly expensive for just one car. A Chilton’s or Haynes repair manual for you car should have that same information too. You local public library may have a copy, gratis. The original factory service manual is probably available as a used paper copy or on CD ROM, for example.
Detailed info for the ABS internals is probably very difficult or impossible to find. I think it is treated as a replaceable unit, not serviceable.
72 mA draw is sort of on the borderline. Most cars are 50 ma or less. My older Corolla is in the single digits, 3 or 4 ma as I recall. But some cars with a lot of gadgets and gizmos are close to 100 ma. A car battery holds about 30 amp-hours of charge, so it should last over 400 hours with 72 mA current draw.
Thanks for the heads up about the repair manuals, I’ll check out my library.
And yeah, 72mA is pretty low, but I live in the city and don’t drive for weeks at a time, so it would be nice not to worry about having to jump when I do need the car. In addition, it would be nice to have a working ABS system, which seems to be the root of the drain issue.
Anyway, you guys have given me a bunch of things to try. I’ll try them out this weekend and update! Thanks!