Should front ABS modulator hum/click when turning on ignition?

[Markg101]

I had an intermittent fault on the ABS. I got away with it for a year but now I?ve terminal blinking.

I?m in the process of problem solving and have a quick question about the front modulator.

When I turn on the ignition I can hear the rear modulator hum for a second. Should the front modulator do the same thing?

Cheers

 

[stgolfer]

Are you sure it's not the fuel pump you are hearing hum?

 

[wjbertrand]

What error code are you getting from the ABS computer?

 

[jfheath]

I'm assuming from your previous posts that this is an ST1100 ?

When you turn on the ignition, the ABS system goes through a checking process and it cycles the ABS modulators to check that they are working. I only ever heard the rear one on my 1100, although both were cycled. I checked by putting my hand on the front one to feel if it was doing anything. It was, but I could never hear it.

I believe that during the self diagnosis process, it turns the motors and reads the sensors to make sure that the output and input to the modulators is working correctly.

What year is your bike ?

There are a couple of fuses for the modulators. Its possible that one has blown. If it has, there is a reason.
The only time that mine ever blew was soon after I had flushed the brake fluid through. I decided to change the pads after I had done this, and of course needed to push in the pistons. This forced the fluid into the rear reservoir. The next time I turned on the ignition, I heard the fuse crack, and the ABS lights flashed. I guess that I had left too much pressure in the system for the modulator to turn, and that this had blown the fuse. I let some bit of fluid out by bleeding the system again, replaced the fuse, reset the fault codes and tried again. Problem cured.

I noticed that you had recently refilled with the brake fluid.

My diagnosis might have been wrong, but whatever the reason, my solution worked.

I had the shop manual on loan fromthe local dealer for a while, while I was tracking down a sensor fault. I discovered the manual to be less than helpful. I wrote up the extra info that I discovered, on my website. It's still there.
The pages describe some fault finding for the ABS system, in particular a way of identifying whether sensors are working.

Click the ABS button on the left to access the page. If your browser cannot use frames, then click this link instead.

There's a video on thepage showing how to recover the fault codes. You may need to have Silverlight installed.
The ABS button on the right of the page links to another which goes through the fault codes, how to recover and how to clear.

Other people on st-owners have all kinds of info pertaining to ABS and ABS II and modulators. The systems are slightly different apparently and it will depend on the year of the bike. Im guessing my 2000 bike was ABS II, but I don't know.

Hope that this helps.

nb - if you clear the fault codes, you will never get them back again. If the ABS system isn't working, then it may not be able to record future fault codes, so make sure that you know what the 2 stored fault codes are before you clear them from memory.

 

[Markg101]

Hi,
Thanks for the responses. Some further info.
2000 ST1100

It is definitely the rear ABS Modulator that is making the noise; you can also feel it

There is no problem code recorded by the ECU; it has never recorded an error code.
When I turn on the ignition only the LH ABS light comes on, both go blank then after a second or two they both come back on. It does the same with or without the button pressed to retrieve the fault codes.

From the manual it looked like the ABS ECU (the one in the white plastic cover) was duff. Picked up another ECU of fleebay, drove for a while and it has the same problem.

The fuses are fine

If I grab the front modulator there is nothing happening when I turn on the ignition. Checked and cleaned all the connectors but still no joy. I'll have a look at the manual to see if any diagnostics can reveal if the modulator is the problem

Cheers

 

[jfheath]

Hi,
Thanks for the responses. Some further info.
2000 ST1100

Same as mine was then.

It is definitely the rear ABS Modulator that is making the noise; you can also feel it

The manual suggests switching the connections over to see if the fault stays with the modulator, or whether it goes to the other one. How you do this has got to be a little awkward. You'd probably have to make up a lead to connect the front connector to the rear modulator.

There is no problem code recorded by the ECU; it has never recorded an error code.

Hmm. Or it has been cleared, and now the ABS never gets initialised far enough to report a new one.

When I turn on the ignition only the LH ABS light comes on, both go blank then after a second or two they both come back on. It does the same with or without the button pressed to retrieve the fault codes.

Mine did that for most of the time I had it. In fact it does it on the video on the web page I sent. I'm almost sure that both came on when I first got it though. ABS still worked correctly.

From the manual it looked like the ABS ECU (the one in the white plastic cover) was duff. Picked up another ECU of fleebay, drove for a while and it has the same problem.
The fuses are fine
If I grab the front modulator there is nothing happening when I turn on the ignition. Checked and cleaned all the connectors but still no joy. I'll have a look at the manual to see if any diagnostics can reveal if the modulator is the problem

Cheers

Its a lengthy, drawn out process, but may have to be done. Did you check for too much pressure from excess brake fluid in the system ?
One other thought. I did have all sorts of weird things happening at one point. I disconnected the ECU completely, went and had a coffee and then reconnected it (with battery disconnected). It (or something related to that) seemed to sort the problem. Like re-booting a PC, I suppose, but logically I cannot think why doing this should work. But it did.

 

[Markg101]

Hi,

The manual suggests switching the connections over to see if the fault stays with the modulator, or whether it goes to the other one. How you do this has got to be a little awkward. You'd probably have to make up a lead to connect the front connector to the rear modulator.

That's a good idea. At least it will rule in or out the modulator

Mine did that for most of the time I had it. In fact it does it on the video on the web page I sent. I'm almost sure that both came on when I first got it though. ABS still worked correctly.

I saw that it did on the video. Mine had both lighting up until the blinking started

Its a lengthy, drawn out process, but may have to be done. Did you check for too much pressure from excess brake fluid in the system ?

Yes, I have checked it as I've changed the pads. It doesn't seem to be a problem

One other thought. I did have all sorts of weird things happening at one point. I disconnected the ECU completely, went and had a coffee and then reconnected it (with battery disconnected). It (or something related to that) seemed to sort the problem. Like re-booting a PC, I suppose, but logically I cannot think why doing this should work. But it did.

I'll give it a try, you never know!


Thanks for your help; you have given me a few ideas to work with.:bow1:

 

[wjbertrand]

I had an intermittent fault on the ABS. I got away with it for a year but now I’ve terminal blinking.

There is no problem code recorded by the ECU; it has never recorded an error code.
When I turn on the ignition only the LH ABS light comes on, both go blank then after a second or two they both come back on. It does the same with or without the button pressed to retrieve the fault codes.

The two remarks above seem contradictory or I misunderstand? A blinking ABS light indicates there is a code stored in the ABS computer. Simply pressing the ABS button, without following the specific code retrieval procedure, will stop the blinking (changing it to constant) but will not retrieve the code. Are you using the procedure in the service manual for retrieving the codes? i.e. with the key off, press and hold down the ABS button, then turn on the key and keep holding the ABS button 'till the dash light goes out then immediately release the ABS button. This should put the computer into reporting mode and you count the short flashes between the long ones.

 

[Markg101]

Hi,

Sorry wasn't specific about the intermittent fault. The fault was that every now and again the ABS lights would come on while driving. It wouldn't stay on and blink. It would just light up for a couple of seconds then went off. This would happen every 3 weeks or so.

I thought it might be an electrical connection so went through the loom. However, the problem remained.

After a year of this, it eventually started blinking continuously, I went through the code retrieval procedure but there was no blinking indicating a code. The LH ABS light came on then off then both lights can on and that was it.

Since starting to blink while riding, It has done exactly same when turning the ignition on and when trying to retrieve the fault code.

Cheers

 

[jfheath]

Some new info then - which may be worth a try, and which isn't in the manual.

First of all - I was wrong about the indicator lights on my old ST1100AY. Both came on and stayed on when starting the engine. I sold the bike ages back so Im working from memory, but I found a vidoeo that I took for my website of me starting it up. They both came on.
What was different from the manual was that in fault diagnosos mode, only the left light illuminated - as you saw in the video.

Put the bike on the centre stand, and knock it out of gear for this next bit.
Enter fault retrieval mode.
When I cleared the fault codes (pressing the ABS/TCS button when the lights flash while retrieving the codes), both lights lit up. (This is contrary to what it says in the manual).

At this point, having just cleared the codes, and with the ignition still on, there seems to be a useful little trick - again not mentioned anywhere that I have seen.
Get some help. Or a mirror. Or both.
Spin the front wheel. The ABS lights will flash if you spin it fast enough.
Spin the rear wheel. The ABS lights will flash if you spin it fast enough.
It isn't possible to spin the wheel and then go and look - you cant get to see the ABS lights quickly enough.

If the sensor isn't working, the light does not flash. So this seems to be a good check to see if the sensors are working. I know this because I had a sensor fail. And I verified the procedure by plugging the front sensor into the rear connector and vice versa. (In spite of the different colour connectors, the front and rear sensors are the same.

What you are descibing sounds like the bike is in this undocumented sensor diagnostic mode as you are riding. Maybe.
So how does it get into this sensor diagnostic mode ? You hold the ABS/TCS switch down when you turn on the ignition. I wonder if the ABS/TCS switch is faulty. I believe that it is a push-to-make contact, rather than a switch. So if it is making the conenction when you turn on the ignition, maybe it is entering diagnostic mode. What happens if you disconnect the switch ?

Or maybe there is a short in the wires going to the switch.

Maybe someone else could verify this behaviour on their ABS on an 1100. Unfortunately I dont have one to try it on now.

 

[Markg101]

Hi,

I've stripped the bike down completely. Gone through all the loom again, giving it a good clean.

Disconnected the ECU overnight. This evening, I turned on the ignition and span the front and rear wheels. Then I plugged in the ABS switch and went through the code retrieval. Hey presto, three blinks indicating the front modulator.

I had a suspicion that the modulator was the problem but now I have some evidence.

Thanks for the advice

 

[wjbertrand]

Try clearing the code first before buying anything. I had a rear modulator code on my '93 and after recording it I just cleared it and the problem never returned. Rode the bike another 2 - 3 years after that.

 

[Markg101]

Fair point. I'll clear and repeat tomorrow.

It would be nice if the error would just go away; it would save me a bit of money!

 

[jfheath]

That sounds like progress. Some odd behaviour eliminated and ecu producing info as it should.

Dont forget that it is possible that there is 'too much pressure' in the brake fluid preventing the modulator from cycling. Also reproduce the result with front mod wired to rear connector and vice versa before Embarking on removal/replacement.

Id also be tempted to start up, get the bike moving and ride with a few hard applications of front and rear brakes. Do this a few times. Note that brakes work perfectly safely even if there is a fault in the abs system. All the abs does is repeatedly release the hydraulic pressure by rotating a 'cam' in the modualtor (simplistic explanation').

As wjbertrand said, now you have proper ecu behaviour, this may clear itself.
But its pleasing to know that you can move forward from here.

 

[Markg101]

Hi there

The bike is now blink free!

After a bit of messing about swapping the ABS ECU it's all working.

I have a feeling there was a duff electrical connection somewhere as I got a few different error codes. After going through all the connections, and using the new ABS ECU I picked up off eBay, all is well.

Thanks for all your help and advice

Cheers

 

[jfheath]

Well done. So nothing to do with what any of us said then ?

Odd that when you first tried the new ECU it was still producing a fault - but it could well be two faults - the connections and the ecu, as you suggested. Looks like you did a pretty good bit of detective work there. Eliminate everything and what's left ..... etc etc.