ABS Relay 1 problem - brake accu?

I am not sure why you are using the diode test position on your meter ... that's a specialized setting to show you the voltage drop across a semiconductor junction.

Are you saying that, previously, commanding relay 2 on did not run the pump?

 

Is the 280 Ω shown in post #20 the resistance from pin 3 to pin 3 of the two relay sockets, with the resistor in place?

That does seem too high.

Does it show as open circuit (offscale resistance) when the resistor is unplugged?

Then, with the resistor unplugged, what is the resistance from relay 1 pin 3, to pin 2 (the black wire) of the resistor connector?

What is the resistance from relay 2 pin 3, to pin 1 (the white wire) of the resistor connector?

 

The wire colors you are reporting between IP1 and B19 are different from the black and white colors shown in the diagram you posted in #17.

Perhaps that is a diagram for the US market or a different model year, and green and pink were used in your area for 2005.

In any case, if you show 0,00 Ω from relay 2 pin 3 to one of those wires, I would lean toward calling the actuator ok. The high resistance between relay 1 pin 3 and the other wire there is what I would want to investigate further.

 

What the diagram is literally showing is that the green and pink wires go as far as a blue connector IP1, where they change to black and white, and proceed to the resistor connector B19.



Perhaps you are saying that your resistor does not have a B19 connector, but its wires are directly attached, and have the blue IP1 connector at the end? That would be a slight design change from what the diagram is showing.

Something also is odd about your measurements in #25. You show 0,00 Ω from relay 2 pin 3 to the green wire. From relay 2 pin 3, I can only understand continuity via BM2, to BM1 internally within the actuator, and to the pink wire at IP1. I do not understand continuity from relay 2 pin 3 to the green wire.

Likewise, I don't understand continuity (or even 1500 Ω) from relay 1 pin 3 to the pink wire. I would understand it to the green wire (but it would be much too high, and need to be investigated).

Is there any chance your description in #25 had relay 1 and relay 2 swapped?

 

That's what I would bet IF you had the green and pink colors reversed in post #25.

So it might be worthwhile to confirm that's what happened, before making expensive bets.

 

I don't know anything about whether the relays ever come on simultaneously.

I guess if you have concluded that the open circuit is between BM1 and BM2 inside the actuator assembly, so that otherwise you'd have to replace the actuator assembly, you could think "what's the worst that can happen if I bridge these two circuits? Will I have to replace the actuator assembly?"

I haven't checked the details here in the diagram or the available trouble codes, but one thing you could run into would be the ECU monitoring the relay outputs to confirm proper relay operation. I know Gen 1 took that kind of monitoring pretty seriously.

 

Yes.

The voltage across the (resistor and motor) in series will be unchanged, so the voltage across only the motor will be less, and the difference will be the voltage drop across the resistor, equal to 0.2Ω times the flowing current.

The flowing current will be the same everywhere in the series circuit: the same in the resistor as in the motor. It will be whatever current the motor draws at the reduced voltage across it, and will equal the resistor voltage drop divided by 0.2Ω.

So it is a chicken/egg question to say whether the resistor decreases the voltage or the amperage "first", but both will be decreased, and by such amounts that the equations work out.

Suppose 20 amps end up flowing (so that the 25 amp fuse would represent a 25% safety margin). Then the voltage drop across that resistor would be 4 volts (20 A times 0.2 Ω) and the heat produced would be 80 watts (20 A times 4 V). That requires a large heat sink.

In fact, a typical 80 watt heat sink would be bigger than that. I think they get away with the smaller size because the fuse amperage probably reflects only the pump motor starting current, its running current is probably a good deal less, and it normally runs for only a few seconds at a time. So the numbers in my example should be considered only that, and probably not what you'd see with a meter there in real life.

So the purpose is that relay 1 can give you a slower, quieter pumping action, when the full pump speed from relay 2 isn't needed.

 

I haven't really watched the pressure sensor voltage per brake press, but the pump every 2 to 4 uses does seem roughly in line with my experience.