ABS diagnostics

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Roger1950
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ABS diagnostics

Post by Roger1950 » Wed Apr 26, 2017 12:56 pm

Good morning all

My ABS warning light has been on for several weeks. No particular incident as far as I know - it just "came on." It is on as soon as I turn the ignition on.

Without going into every last detail of my (extensive) troubleshooting, I have checked wheel sensors (continuity and resistance), and continuity of wiring right up to the ABS control unit. The reason I focused on the wheel sensors (especially the right rear) is that the fault code being indicated is 3 flashes. That's all - no initial single flash - only 3 flashes with a few seconds between the group of three. I'm seeing the flashes on the ABS warning light itself when the appropriate pins are connected at the diagnostic box. I can't get the test LED to light at all at the diagnostics box (which I find a bit puzzling having read about all the work others have done on this problem.)

My specific questions come down to the following:

- what is the "normal" sequence of self-test of the ABS system? What should you see when you turn on the ignition?
- does anyone have any idea what the code might mean (i.e., are there any other warnings that show up on the ABS light, but that are not part of the ABS system?);
- how do you reset the ABS/ECU (I'm wondering if I have cleared the fault but the warning needs to be reset.)

Thanks for any ideas on this

Roger

1995 2.5D Auto 4FWD AFT
1995 2.5D AFT 4WD Auto
Bongolia
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Re: ABS diagnostics

Post by Bongolia » Wed May 03, 2017 12:59 pm

Roger1950 wrote:Good morning all

My ABS warning light has been on for several weeks. No particular incident as far as I know - it just "came on." It is on as soon as I turn the ignition on.

Without going into every last detail of my (extensive) troubleshooting, I have checked wheel sensors (continuity and resistance), and continuity of wiring right up to the ABS control unit. The reason I focused on the wheel sensors (especially the right rear) is that the fault code being indicated is 3 flashes. That's all - no initial single flash - only 3 flashes with a few seconds between the group of three. I'm seeing the flashes on the ABS warning light itself when the appropriate pins are connected at the diagnostic box. I can't get the test LED to light at all at the diagnostics box (which I find a bit puzzling having read about all the work others have done on this problem.)

My specific questions come down to the following:

- what is the "normal" sequence of self-test of the ABS system? What should you see when you turn on the ignition?
- does anyone have any idea what the code might mean (i.e., are there any other warnings that show up on the ABS light, but that are not part of the ABS system?);
- how do you reset the ABS/ECU (I'm wondering if I have cleared the fault but the warning needs to be reset.)

Thanks for any ideas on this

Roger

1995 2.5D Auto 4FWD AFT
Sorry this didn't flag up for some reason.
Normally it would be light on for a few seconds whether cranking or not this carries out the electrical self checks.

No idea on the code.

I believe the Bongo can be reset by removing the battery connections for about half an hour or so if that fails try unplugging the control unit with ignition off for half hour.

Note you may go through the self check sequence and all appears well then when driving faster than 5 mph it may come up again. This usually indicates a fault with the mechanical side not the electrical i.e. incorrect wheel size, broken reluctor wheels, contaminated sensors etc.
Roger1950
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Re: ABS diagnostics

Post by Roger1950 » Fri May 05, 2017 9:01 am

Thank you very much.

I will try as you suggest.
1995 2.5D AFT 4WD Auto
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Re: ABS diagnostics

Post by g8dhe » Fri May 05, 2017 9:23 am

The known codes are listed on this site http://www.philmcfadden.co.uk/MazdaDiagnosticBox.htm
Geoff
2001 Aero V6, AFT, full side conversion.
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Roger1950
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Posts: 24
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Location: Wirral

Re: ABS diagnostics

Post by Roger1950 » Fri May 05, 2017 9:41 am

Thanks Geoff

I think I must be doing something wrong when I look for the fault code. I have read dozens of posts concerning the ABS, and I should be getting a double-digit code, not just three flashes, repeated. Also, it is the ABS warning light itself that is flashing, not the LED patched into the diagnostic box.
I'm going to disconnect the ABS computer for a couple of hours as Bongolia suggested, just to see if it might benefit from a reset.

Also Geoff I'd like to say a big thank-you for the work you and other Bongonauts have done in getting the wiring diagrams etc., available to us. I wouldn't have stood a chance of even getting this far without having them.

Roger
1995 2.5D AFT 4WD Auto
Bongolia
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Re: ABS diagnostics

Post by Bongolia » Fri May 05, 2017 4:31 pm

Roger1950 wrote:Thanks Geoff

I think I must be doing something wrong when I look for the fault code. I have read dozens of posts concerning the ABS, and I should be getting a double-digit code, not just three flashes, repeated. Also, it is the ABS warning light itself that is flashing, not the LED patched into the diagnostic box.
I'm going to disconnect the ABS computer for a couple of hours as Bongolia suggested, just to see if it might benefit from a reset.

Also Geoff I'd like to say a big thank-you for the work you and other Bongonauts have done in getting the wiring diagrams etc., available to us. I wouldn't have stood a chance of even getting this far without having them.

Roger
What pin are you taking your reading from?
Are you using an LED or straight to ground.?
Roger1950
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Re: ABS diagnostics

Post by Roger1950 » Fri May 05, 2017 4:59 pm

I have been trying to follow the instructions in the Factsheet: using a jumper to connect the ABS diagnostic pin (3rd row down, 2nd from right) and the ground pin (2nd row down, 4th from the left.)
Then the factsheet says the LED should be connected to the positive pin (bottom row, 3rd from left.) But I realise now whilst trying it again, there is no pin in that slot. Similarly, there is no pin in the 4th row, second from right which is supposed to be the ABS fault code pin.
So I wonder if I'm misreading the instructions, or....?
1995 2.5D AFT 4WD Auto
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Re: ABS diagnostics

Post by Bongolia » Fri May 05, 2017 5:02 pm

Roger1950 wrote:I have been trying to follow the instructions in the Factsheet: using a jumper to connect the ABS diagnostic pin (3rd row down, 2nd from right) and the ground pin (2nd row down, 4th from the left.)
Then the factsheet says the LED should be connected to the positive pin (bottom row, 3rd from left.) But I realise now whilst trying it again, there is no pin in that slot. Similarly, there is no pin in the 4th row, second from right which is supposed to be the ABS fault code pin.
So I wonder if I'm misreading the instructions, or....?
Fact sheet on here BF?
Roger1950
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Re: ABS diagnostics

Post by Roger1950 » Fri May 05, 2017 5:03 pm

yes - the one updated 19 January 2015
1995 2.5D AFT 4WD Auto
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Re: ABS diagnostics

Post by Bongolia » Fri May 05, 2017 5:06 pm

Roger1950 wrote:yes - the one updated 19 January 2015
Got it.
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Re: ABS diagnostics

Post by Bongolia » Fri May 05, 2017 5:23 pm

I think you have the wrong pins there. Let me get to pc and I can check your config.
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Re: ABS diagnostics

Post by Bongolia » Fri May 05, 2017 6:15 pm

Bloody W10 is doing an update!
As I see that the fact sheet diagram is upside down to how its presented in the vehicle.Which would put you in the wrong pins.
I.e. you would need to be 3rd row up second from left for TBS.
Have I got that right?
Roger1950
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Re: ABS diagnostics

Post by Roger1950 » Fri May 05, 2017 6:20 pm

Thanks!
I did wonder if there was something amiss, but it doesn't "work" upside down, either.
I'll look at it tomorrow - we have stopped for apero's.....
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Re: ABS diagnostics

Post by Bongolia » Fri May 05, 2017 6:32 pm

Good idea..
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Re: ABS diagnostics

Post by g8dhe » Fri May 05, 2017 6:59 pm

There are variations depending on the year and engine type of the diagnostic connector, as outlined on the web page http://www.philmcfadden.co.uk/MazdaDiagnosticBox.htm It seems not all vehicles are the same, so you may need to take that into account as well.

The ABS is 4th row from top 3rd from right for the Lamp and the link is 3rd Row and 2nd from right.
Geoff
2001 Aero V6, AFT, full side conversion.
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