Technical Bravo ABS wheel sensor code

[PineKuusman]

The car is a Fiat Bravo 2010 and the ABS is a Bosch 8.0 vdc.
The car started to complain about the Abs sensor on the right front wheel that winter. Now in the spring I changed the sensor and the same situation continued after resetting the codes. I cleaned the magnetic bearing ring and measured wires from the abs controller to the sensor.

MES gives a speed value to the right front wheel when the tire is in the air and i rotates by hand the tire. But there are special spikes in the graph, i.e. sometimes when driving, the speed drops from 40km/h to 20km/h or even to zero and immediately returns to normal. After that will be an indicator light on the instrument panel. Other sensors also show such rapid drops from time to time.

When I measured the corresponding abs of the Stilo and manually rotated the tire, no corresponding drops were visible in the graph.

Any ideas if that Bravo could need e.g. front bearing replacement or e.g. brake bleeding/fluid change etc. Or should I start looking for a new control unit.

 

[bugsymike]

Re the front wheel bearing magnetic sensor, they must not be in contact with anything magnetic like a magnetised screwdriver etc. when cleaning as it destroys/damages the magnetic vanes in/on bearing. I have a tester from SKF bearings that looks like a credit card and you hold it against the bearing and it has iron filings trapped in the card which shows exactly the vane layout or damage to the vanes.
With powered/active ABS sensors if the wiring has a break a fault can show as soon as you turn on ignition key, where as non powered "Hall effect" ones only show an error after wheels are moving.
However if yours works to start with , say in a straight line, but fails after going over a bump or turning the steering etc. it may indicate a break in a wire or poor connection.
I can't see changing the brake fluid making a difference.
Some cars use a VSS speed sensor like the old speedo drive but with an electronic sensor in the gearbox, so if that was faulty it may affect things.
If it doesn't have that then the ABS computer may take the four ABS sensor readings to calculate road speed , but I don't know for sure.
I had a Skoda Scout that I tried an ABS sensor , then learnt that those and VW Tiguans had an issue with the ABS wiring loom in the wheel arch, so I replaced that. Unfortunately on mine the fault was much further in the wiring where it went from the engine compartment, doubled back into the interior behind the glove box then went back to the engine compartment to the ABS pump/module, so was a pain to find the problem.

 

[PineKuusman]

Thank you for reply. I measured wirings again from abs-ecu to sensor connector and those seems to be okay. After reseting error codes I can drive about 200meters and error for right wheel sensor reappears. It's like normal road, no special bumps or curves.

Maybe I should connect front wheel sensors otherwayaround and see if error code jumps to left side.

 

[bugsymike]

Thank you for reply. I measured wirings again from abs-ecu to sensor connector and those seems to be okay. After reseting error codes I can drive about 200meters and error for right wheel sensor reappears. It's like normal road, no special bumps or curves.

Maybe I should connect front wheel sensors otherwayaround and see if error code jumps to left side.

You could try that if they fit, some are handed.
I don't know specifically about your powered ABS Sensors, but are you certain they should have 8 volts? Is that the same measured voltage at both sides of the car, as on my Skoda I had around 11 volts on working O/S and a much lower reading on the faulty N/S.
Very unlikely , but is there a difference in rolling circumference between both the front wheels.
This is my SKF ABS bearing tester

 

[PineKuusman]

This was yesterday. Some spikes in right wheel sensor and after that 80seconds - error code. Have to test more in the evening.

 

[bugsymike]

This was yesterday. Some spikes in right wheel sensor and after that 80seconds - error code. Have to test more in the evening.
View attachment 444570

It does seem to indicate a intermittant issue possibly like a damaged wire/connection, rather than the other things I suggested.
Is it possible to test the wires or replace them up to the ABS pump ECU.
I see your yellow right rear seems to spike also at different times.
Have you unplugged carefully and sprayed with proper electrical switch cleaner (not WD40) the ABS main plugs at the ABS pump ECU with ignition off?

 

[PineKuusman]

In the meantime, I didn't do any testing/fixing yet, but I checked the fault codes from the car with the elm327 cable.

There is something special in that abs module or elsewhere in the can bus, when I looked at the bcm (body computer) fault codes yesterday, there were several of them related to the can bus and then a reset for them. There was also a code related to the can bus on the power steering, etc. According to the wiring diagram, the can bus goes through the abs-ecu to control the motor. Well, abs, ecu, power steering, yaw sensor (tilt, etc.) always showed up for bcm. the fault code of the can bus back after resetting. Maybe they have also come when I disconnected different connectors earlier. They always seem to appear as a group when the abs-ecu has communication problems.

I reset the fault codes from different modules and with a small risk did the proxy alingment function and bcm then deleted the abs completely from its memory :roll:

Well, now i need to check if there is any loose contact in that ABS-ECU connector. However, the car starts and you can drive it without abs and speedometer :|

A few years ago, an already used abs module was bought on the shelf due to similar can defects, so maybe now it needs to be installed in its place. At that time, the repair was successful with fault code resets/proxy alignment. At least at this time, Multiecuscan did not connect to abs or power steering. For the summer MOT, the goal would be to get this still a valid car.

 

[PineKuusman]

I could update this little bit if someone is interested in the topic later... I got that module pack back to bcm.
There is a special wire jungle here though if you use Multiecuscan. It goes roughly as follows:
- with the green adapter, the elm327 wire can be used to access the abs-ecu and the power steering
- the elm327 cable allows access to most of the modules, but it also causes interference to the can bus and error codes for a few modules. For example, the car won't start if the wire is in place.
- with the k-line wire you can access e.g. the engine ECU and abs

Well, yesterday I made that proxy alingment with an elm327 cable without an adapter, which removed the abs, engine ECU, etc. from the bcm.
Today I got them back, when with the green adapter I first removed the fault codes from the abs and straight continuing to the proxy alingment. After that the modules returned to bcm. Finally, with the k-line cable, also removed the canbus code from the engine ECU.

Now i continue with that sensor problem

 

[PineKuusman]

llittle bit update, that while i connected wires otherwayaround error code jumped to the left wheel. I suppose that it must be bearing after all that caused these errors.

 

[bugsymike]

llittle bit update, that while i connected wires otherwayaround error code jumped to the left wheel. I suppose that it must be bearing after all that caused these errors.

Not convinced, time will tell.