General Category > ABS related issues
F650 CS 2 - spark 2005 : 1508: Rear sensor fault, signal implausible.
stardust_59:
Next step w.r.t fault diagnosis will be the setup of a test harness to access the connector between Rear wheel sensor and ABS.
It is mechanically next to impossible to hook up 'normal' test leads to the male connector of the sensor.
This connector seems to be proprietary BOSCH - it does not resemble any of the AMP product line connectors.
Thus - 22-28 AWG male & female crimp inserts well be used to access the pins / slots of both ends with accessible leads in between.
Parts are ordered.
This will allow to check the first part of the signal path.
The dashboard connector seems to be accessible from reverse side.
This leaves in situ access of ABS and BMS connections to be resolved.
I would be happy to receive any hints on how to access the further signal path with all components in place - with priority on the ABS ==> Dash path from ABS connector location.
A9190 / 24 ==> X9001 / 3 - cable yellow 0.5mm (sheet VIII ABS)
Not sure if the use of a LED for H9190 (ABS warning lamp) has an impact in the behavior.
Secondary path to A9500 / BMS can be checked 'dry' - by just puling connectors off and checking lead resistance from X9001 / 6 via X9409 to units A9500 (BMS) / 21 color Blue Yellow, 0.5mm . (See sheet VII of wiring diagram)
There are no active components in that path.
WayneC:
The sensor is the DF11s & male/female pins from STD electronics 0.1" connectors can be used at the socket under the seat to connect a 100 ohm resistor for signal testing as per the thread I referred to, you wont need to do anything re the Dash/BMSC other than confirm continuity of the wiring between them
stardust_59:
WayneC - thanks.
Did some measuements and can confirm.
Pins are really thin though - thinner than the usual breadboard headers..
Waiting for material to arrive for making a test harness for hooking up my scope.
Might need it more than once and I am not a fan of shaky conections when scoping...
stardust_59:
The saga continues...
Meanwhile the rear sensor was replaced with a new one (OEM BMW part).
Measurements were made and the sensor shows signals to the ABS.
After replacement of the rear sensor the symptoms persists:
No speedomeeter readout, ABS failure / blinking lamp.
The lead from the ABS connector to the Speedometer / tachometer unit connector shows continuity,
as well as the lead from the BMS connector to its connector pin on the Speedo unit.
I checked the Speedo unit's input stage for the ABS rear signal and discovered that there is in fact an analogue input stage using a two or three stage transistor inverter.
Why this was not implemented using an OP amp is beyond me.
I will later supply pictures of my findings on the speedo PCB.
As the error persists after replacing the rear sensor - I thought that the connection of the Sensor Input from ABS to the output pin for the BMS on the Speedo PCB might be defective.
I was lucky to get a working 2000 F650 / ABS Speedo unit which was used on the F650 CS - the symptom remains.
No speedomeeter readout, ABS failure / blinking lamp.
After a few meters (about 100 m) the ABS light goes on and indicates ABS error.
I will yet have to read out the error but I guess it will be the same as before.
1508: signal implausible.
The last thing that possibly remains to do is to re-check the leads and measure signals on the Speedo PCB input side - after the Speedo unit connector.
Is there any thing else that might have to be taken into consideration as fault cause ?
WayneC:
--- Quote from: stardust_59 on April 29, 2018, 08:29:30 PM ---I checked the Speedo unit's input stage for the ABS rear signal and discovered that there is in fact an analogue input stage using a two or three stage transistor inverter.
Why this was not implemented using an OP amp is beyond me.
--- End quote ---
The Dash input stage is designed to work with the raw sensor signal input on non ABS models and then the signal from the ABS on ABS models, the first transistor detects the 20ma current switch from the sensor, from there the signal goes to the processor and separately out to the BMSC
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