Home Repair detail German French Brain for sale Feed back Modulator test.

How to check the modulators dynamically, including an ABS relay check.
Test section was revised on August 29. 2014
Disclaimer: The author of the following info does not take any responsibility for any loss or damage to the modulators or anything else resulting from the tests or the subsequent use.
The following modulator test will sort out whether the true defective part is the ABS brain or the modulator if the ABS error code you got is 1 or 2 or both 1 and 2.
Note that not only the modulator, but also a defective brain can cause error 1 or 2 or both 1 and 2.
  1. How to actively or dynamically test the ABS modulator and ABS relay.
  2. A look at the inside of the modulator with descriptions.
  3. Control circuit block diagram.

1. Modulator test. Making test wirings required for modulator testing.
a.Required parts.
* parts name Spec how much or how many
1 flat pin 2.5 to 3 mm width, 0.2 to 0.3 mm thick, 8 to 12 mm length 4
2 small wire approx. 30 AWG. or 1 mm2 thin wire one meter
3 small alligator small 2
4 resistor 1 Kilo Ohm.1/8 watt one
5 heat shrink tube 3 to 4 mm dia. and 10 cm or 4 inch long. used to cover the resistor. one

b. completed sample picture


c. making wiring.
wire name used in testing end to end length, minimum remarks color in the above picture
1 1419 13 cm or 5 inch both ends have flat pin brown
2 TRIG 20 cm or 8 inch flat-pin to 1 kilo ohm to alligator in series white
3 RLY 60 cm or 24 inch flat-pin and alligator yellow

2. testing

Turn off ignition.

Pin assignment of the 25pin ABS connector
Wiring loom is conected on opposite side. on the left.

Common connection.
a. connect pin 14 and 19 of the 25 pin ABS connector using the 1419 wiring.
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2.1 Front modulator test
Be ready to record the measured resultant voltages V10, V11 and V12.
a. Check the battery voltage. It must be more than 12 volt for proper operation of the modulator and ABS.
b. Connect pin 17 and battery plus using the RLY wiring, the alligator end goes to battery plus.
c. You will hear an ABS relay click and possibly a mosquito sound from the modulator.
d. Connect a DC volt meter to pin 10 and battery ground: The reading must be 12 volt or higher. Name this reading as V10 for later reference.

e. Connect one end of the TRIG wiring to pin 6 and touch the other end to battery plus.
Maximum duration of this connection is 5 seconds to avoid damage to components.

f. While doing above, read the voltage between pin 10 and groud. It is OK if the reading is between 1 and 6 volt. Name this as V11.
g. Connect the DC volt meter to pin 9 and read the voltage while touching the TRIG wiring to the battery plus.
It is OK if the reading starts from zero, then going to a value between 1 and 8V, and then going back to zero, all within 1 second. Name this V12.
h. Remove all test wiring.
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2.2 Rear modulator test
Be ready to record the measured resultant voltages V0,V1, and V2.
a. Check the battery voltage: It must be more than 12 volt for proper operation of the modulator and ABS.
b. Connect pin 17 and battery plus using the RLY wiring, the alligator end goes to battery plus.
c. You will hear an ABS relay click and possibly a mosquito sound from the modulator.
d. Connect DC volt meter to pin 12 and battery ground: The reading must be 12 volt or higher. Name this reading as V0 for later reference.

e. Connect one end of the TRIG wiring to pin 7 and touch the other end to battery plus.
Maximum duration of this connection is 5 seconds to avoid damage to components.

f. While doing above, read the voltage between pin 12 and ground. It is OK if the reading is between 1 and 6 volt. name this V1.
g. Connect the DC volt meter to pin 11 and ground and read the voltage while touching the TRIG wiring to the battery plus.
It is OK if the reading starts from zero, then going to a value between 1 and 8 V and then going back to zero, all within 1 second. Name this V2.
h. Remove all test wiring.
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3.Decision.Use the test results to determine which component is defective or good as shown in the tables below.
dm: does not matter, ok: measurement was ok, not: was out of spec.
For front modulator.
Decision V10 V11 V12
ABS relay,
modulator are ok
ok ok ok
modulator maybe defective ok not dm ABS relay or 5 pin connector maybe defective if V11 is below 0.1V
modulator maybe defective ok ok not
bad battery or ABS relay not dm dm

For rear modulator.
Decision V0 V1 V2
ABS relay,
modulator are ok
ok ok ok
modulator maybe defective ok not dm ABS relay or 5 pin connector maybe defective if V1 is below 0.1V
modulator maybe defective ok ok not
bad battery or ABS relay not dm dm

As I mentioned elsewhere it is not possible to repair the modulator. Please find a good one from a scrapyard near you.
The end of modulator and ABS relay test.

2. Look at the inside of the modulator with descriptions. Note, dismantling the modulator will destroy it!
Seq. Image Description
1 This is the electric side housing of the modulator. The connection from the ABS wiring harness to the internal circuit board is made through the black plastic insulator/holder and it makes the repair of the circuit difficult because you can't undo the connection to repair it without damage to the connection.
The pressure sensor is made of piezoelectric material and is placed in the bottom centre of the hole; it checks the operation of the modulator.
2 This is the pressure sensor and it is connected to the solenoid control circuit.
3 This is the solenoid (magnetic force generator) control circuit and two high strength coil springs.

In a normal state the springs force the hydraulic valve mechanism into the normal operation mode. Braking force is controlled by pedal or lever pressure only.
4 Same as above, with the pressure plate placed on top of the springs.
5 This is the pressure shaft, it has two duties.
One is to transfer the spring force to the mechanical valve in the hydraulic unit in order to set it into normal operating state and the other one is to transfer the opposite force generated by the solenoid to the pressure sensor and also to put the hydraulic unit into the ABS activation state.

The left side end of this shaft goes into the hole on the pressure plate above.
This shaft goes through the secured pole and the movable pole to transfer the forces.
6 This is the secured pole. it is a part of the ABS body and was machined to this shape.

You can also see the connector that connects the solenoid and control circuit.
7 Overall view of the same parts.

As you see, the construction of the main body / hydraulic portion makes returning the modulator to the pre-disassembly condition almost impossible.
8 This is the solenoid,
it produces the strong electro-magnetic force which is higher than the force of two coil springs and thereby generates the force required to bring the modulator into the ABS active state.

The resistance value of this coil is only 0.150 ohm and the resistance including the control circuit is only 0.20 ohm.
So this modulator could draw up to 50 amps under 10 volt supply voltage.

It has an over current limiting circuit in the control circuit to cut the current if it is more than 50 amps.

You must be very careful since under the above current draw condition the circuit generates 500 watts of heat !!!!.
Putting the modulator under this condition for more than 10 sec. should be avoided.
9 This is the movable pole.
It is pushed toward the hydraulic valve by the force of the two springs so as to put the modulator in the normal state.
Once the ABS firing signal arrives at the control circuit then the solenoid is activated. The solenoid force is resisted by the spring force but the magnetic strength, this pole moves to compress the springs and the hydraulic valve goes to the ABS activation state.

The springs return it to its original position when the firing signal ends.
10 This is the main body of the modulator.
The secured pole is inside the left hand end.

The circuit portion sits on the left side of this and the hydraulic portion sits on the right hand side end of this body.
11 This is the hydraulic portion,
you see three bearings touching, they are part of the hydraulic valve system.

When in a normal state, the bearings are pushed by the movable pole and the bearings push hydraulic valves.

The valve is of a coaxial construction, the inner valve controls the position of the ball valve that controls the fluid flow from master cylinder, and outer portion works as the variable capacity chamber that increases its capacity when the ABS is active and then reduces under normal operation.
12 The bearings can move and work like levers also changing the direction of force.
13 The inside of the hydraulic valve.
A metal ball acts as a control valve to control the fluid flow from the master cylinder to the brake system.

When under the ABS activation, the brake pedal or lever becomes stiff because the ball valve is being held closed.
14 The inside of the hydraulic circuit.

You can see the pin at the centre of the hole, it is the ball valve position control pin that is controlled by the bearing mechanism, and it pops up under normal operation so that the ball valve can open to allow free fluid flow.

When it goes down, the ball valve closes the channel and the fluid flow is blocked.

At the same time, the variable capacity chamber increases the capacity, thus reducing the brake line pressure and the brake force so as to allow the wheel to recommence rotating and bring the bike to the stable state.


3. Control circuit block diagram.




直線上に配置



inserted by FC2 system