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I had this problem ever since I bought my car 7-8 years ago. The ABS light turns on rather randomly. Sometimes it stays off for months. Sometimes it turns on and of multiple times per day. It's a Ford Focus 1.8 tdci from 2004, 100 HP.

I did check the following:

  • brake fluid level and cap checked (replaced with one from another car to see if the problem disappears, it didn't)
  • DTC error codes read with Forscan: no error codes in general, no error codes from the ABS module. The only place in the OBD scanner tool where I could find something remotely related to this problem was the "ABS warning indicator" which was consistent (on/off) with the warning light on the dashboard
  • reading ABS data while the vehicle is moving: all wheel sensors give the same speed reading in a straight line (with the ABS warning light on or off)
  • performed the Forscan OBD ABS troubleshoot test: the test performs ok and no errors are found
  • sometimes, after washing the car, the ABS light stays off for some time
  • I tested the car during winter: the ABS works even if the ABS warning light is on

I'm not sure what to do next in order to solve this problem. I have a few questions

  1. Is it possible that I have a faulty sensor even if the speed read for each wheel is consistent with the speed of the vehicle? Can sensors be bad without giving error codes?
  2. What are your suggestions regarding what I can try in order to isolate the problem?
  3. Is it possible that this is a dashboard problem? I took it off and saw some bits of corrosion on some of the nodes on the electronic board.
  4. If the ABS module is available in Forscan for the live-sensor data, that means that DTCs should also be available, if present? Update: I took one of the sensors off and managed to get an error code. Therefore, indeed, the ABS light stays on without any error code.

Thank you in advance.

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  • Have you checked the level of the brake fluid in the master cylinder?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 2, 2021 at 21:21
  • @Pᴀᴜʟsᴛᴇʀ2: I just checked the level in the reservoir. How do you check the level in the master cylinder?
    – Beni Bogosel
    May 2, 2021 at 22:42
  • The reservoir was what I was talking about. My apologies if it was confusing.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 3, 2021 at 0:06

2 Answers 2

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Speed sensors are prone to be intermittent in failures. If they can easily be removed and cleaned without breaking them cleaning then might help. I believe this car has a pedal pressure sensor that is found by the brake light switch. I'm confused by the anti locks working during an illuminated ABS light. That shouldn't happen. I'm assuming your scanner can read ABS codes, but if the light turns on, there is a code stored. You should confirm which codes these are by verifying the scanner is able to read these. Or better yet find another scanner that can read ABS codes for this specific vehicle. This should be done before any other parts are replaced. The only thing I would highly suspect at this point without a code would be a bad brake fluid level sensor or the wiring or connectors to it. I know you replaced it with a used one, but that doesn't mean it's good.

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  • Thank you for your answer. I'm assuming the scanner can read abs codes since it connects to the module, shows live speed sensor data and indicates that there are no error codes stored (continuous or intermittent). I checked again this morning. ABS speed sensors show the same speed as the vehicle speed data even when the abs light is on... The brake fluid level sensor I checked did work fine on the other car.
    – Beni Bogosel
    May 3, 2021 at 6:47
  • I guess I should take the sensors down one by one and clean them.
    – Beni Bogosel
    May 3, 2021 at 6:54
  • When checking wheel speed sensor a for uniformity, make sure one doesn't cut out at low speeds. They should all report consistent at 4 mph and higher. Some later models cut in before 4 mph, but earlier models do not register below 4 mph. I would like to avoid removing sensors because sometimes they can be damaged from removal. But I'm in the salt belt also. It still bothers me that no codes are present. If the scanner shows no codes when the light is on, you might want to try another scanner.
    – Jupiter
    May 3, 2021 at 9:46
  • I checked and they show the same speed at 2-3 km/h or at 50 km/h. The scanner is surely good. I disconnected one of the sensors (careful not to break it) and an ABS error code popped up. I connected it back, cleared the errors, and the ABS light still turns on and off from time to time... When I have the time I will do this for every wheel. Maybe I'll also try a different instrument cluster to see if tha makes a difference or not...
    – Beni Bogosel
    May 3, 2021 at 11:41
  • I swapped the instrument cluster with another used one. The ABS light is gone and never appeared during a few hundred kilometers. Since there were signs of corrosion on the board from the old IC, I guess that this was the issue causing the ABS light to turn on.
    – Beni Bogosel
    May 11, 2021 at 8:07
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It turns out that this was an Instrument Cluster problem. After swapping the instrument cluster with a different one the ABS light stays off.

Therefore if the ABS lights (or other lights) come on without generating any error codes you might try to see if the problem is the Instrument Cluster itself.

Update: I tried restoring the old instrument cluster since the new one had the wrong mileage. It turns out that cleaning all the rust points using a contact spray did the job and the ABS light is off now.

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