Another ABS/TCS code puzzle...

[Martyn]

Hi, I'm writing this over lunch and in haste, if it's not clear tell me what you need to know

:redface:

For quite a while now the ABS has kicked in at slow traffic stops. ( 1993 manual 5sp unmodified ).

Thinking it might be a wheel sensor I pulled ( or tried to pull ) the self-diagnosis codes this morning.

I know the TCS and ALB share the same wheel sensors

I’ve got the relevant manual page in front of me ( 19-31 ) but can’t make sense of what I see.

Can anyone interpret this?


NORMAL SEQUENCE ( diagnostic plug not bridged )

Ignition switch on, engine off

OIL BATTERY ALB TCS all on constantly ( SRS Airbag light glows briefly, then switches off )

Ignition switch on, engine starts and during normal driving

All tell tale lights off

As far as I know this is all normal



DIAGNOSTIC SEQUENCE ( with the bright blue connector bridged )

Ignition switch on, engine off

OIL CEL BATTERY on constantly ( SRS Airbag light glows briefly, then switches off )

TCS flashes once – as the doors are locked by my car’s security system - then remains on constantly

ABS light off

Ignition switch on, engine starts

CEL light remains on, all others, including the TCS light, go off.

 

[Larry Bastanza]

For quite a while now the ABS has kicked in at slow traffic stops.

Please explain what this means.

Does the ABS pump engage?

Does the pedal kick back at you when you apply the brakes?

What pads are installed?

What wheels are on the car?

Your scenario above shows that nothing is wrong

HTH,
LarryB

 

[Martyn]

I think because the ABS light isn't illuminating to show a fault while I'm driving the system isn't registering a code for me to download. BUT, there has to be a fault of some kind!

This is what happens - When I slow down gradually to make a traffic stop as the car draws to a halt ( around 5mph or less ) the ABS system kicks in and I feel the brake pedal shudder. The system works fine when it has to ( which is never during my normal life but I have tried it on gravel surfaces and it operates perfectly ). It's an intermittent fault, sometimes it doesn't happen for days but over the last four or five weeks it's been ever present.

When I brake normally at regular driving speeds ( for corners and such ) or to slow down when I see a speed camera ahead :tongue: - the ABS does not kick back.

As for wheels and pads, yep, I've got 'em, one set on each corner of the car! Nothing upmarket about them, they're pretty much stock parts. When the car had its MOT test ( a UK government check on road worthiness ) last week the mechanic told me that one of the back brake calipers was a little sticky as the brake reading was slow to fall after the pedal was released.

That's all I know but I'll happily go and poke around the car some more if you need me to.

 

[Larry Bastanza]

Tires and wheel sizes?

Year of car?

It really sounds like your have a wheel actually locking up, the question is why.

If you do not have any indicators, of codes I find it hard to think a wheel speed sensor is bad, but.....stranger things have happened.

Intermittent problems are the hardest to figure out.

Regards,
LarryB

 

[Martyn]

I wonder whether the "sticky" rear caliper is locking up? To be honest I think I'd feel it but at less than 5mph, who knows??

That might explain the absence of fault codes ( if the rear wheel really is locking up and the ABS kicks in, then that's not a fault, that's its job! )

1993, standard wheel sizes for that year - small on the front, big on the back...

 

[drew]

Just a guess:

Clean off the wheel sensors....they are magnetic and tend to accumulate trash.

There might be enough magnetic trash to occlude "seeing" the hub --thinking the wheel has stopped--that it is triggering a de-locking attempt.

I suspect you can also swap out sensors and see if the problem moves around.

 

[Martyn]

I've got the manual open at p 19-31 which shows where the front wheel sensors are, but where are the ones on the rear? I think they're somewhere near the hubs but beyond that, I'm lost.