ABS light HELP PLEASE

[gavinbray]

Hello,car is a 1989 944 2.7. My car is off the road for the winter months while i get some work done(just replaced the front wings and a few bits and pieces) The car had been sat in the garage for 2 months and the battery had gone pretty flat,i needed to move it so i jumped it off my other car,took her for a quick spin and no problems.I parked her back up in the garage and took the battery off to chrage it up(around this time i found out there is no manual override for the electric boot release[]) When the battery was charged i stuck it back in and all fine apart from the ABS light is on and stays on,it has been suggested to me that this is because the battery was disconnected and that it needs resetting,is this true? and if so how do i reset it,i have a very friendly garage down the road with the normal car diagnostic computer,but will this fit a 1989 porsche? Any help would be grand.

Thank you

Gavin.

 

[dlknight]

ORIGINAL: gavinbray

Hello,car is a 1989 944 2.7. My car is off the road for the winter months while i get some work done(just replaced the front wings and a few bits and pieces) The car had been sat in the garage for 2 months and the battery had gone pretty flat,i needed to move it so i jumped it off my other car,took her for a quick spin and no problems.I parked her back up in the garage and took the battery off to chrage it up(around this time i found out there is no manual override for the electric boot release[]) When the battery was charged i stuck it back in and all fine apart from the ABS light is on and stays on,it has been suggested to me that this is because the battery was disconnected and that it needs resetting,is this true? and if so how do i reset it,i have a very friendly garage down the road with the normal car diagnostic computer,but will this fit a 1989 porsche? Any help would be grand.

Thank you

Gavin.

Sounds like the ABS computer has packed up, its located in the drivers footwell on the right-hand side. First thing to do is make sure everything is dry in case its damp electronics. Does the light stay on after the initial pre-ignition warning lights or does it come on after you pull away? If it is on as soon as the ignition is turned on it is likely the computer otherwise if it comes on after pulling away it could be a wheel sensor.

I managed to pick up a 2nd hand ABS computer off the bay when mine went south.

Dave

 

[gavinbray]

Cheers Dave,i will have to check when i have time but i THINK it comes on straight away and stays on,is there anyawy of testing to be sure of what is up before buying parts? if parts are needed i have a friendly 944 parts chap not too far from me,but still i would like to be sure before i buy stuff.

Cheers
Gavin.

 

[amrbose14]

Check the relay in the fusebox in the engine bay before worrying about the ABS ECU itself. I had exactly your symtpoms under very similar circumstances (car off the road for a bit, needed to charge the battery). Annoyingly I'd just adjusted a wheel bearing, so I was convinced I'd disturbed a sensor - which did not make sense as the light came on as soon as I started her up. Anyways.... you can check the relay or replace it with a known good one. I got mine for £25 2nd hand off ebay (I've seen £70 for new).

cheers,
Chris
87 220T.

 

[gavinbray]

Guys this is all good help thank you. My friendly parts chap has an ECU for me for £35 if needed,but i am gagging for some tests here chaps.How would i test the relay?

Cheers Gavin.

 

[amrbose14]

Well now you've called my bluff and I have to admit I took it to a friendly electronic engineer. The relay contains a diode and I was worried about damaging it (on the chance that it was working).

What you need to do is take it out and put 12V across pins 31 and 15, but I can't remember which pin takes the ground and which takes +12V. I'm not completely sure if you can do any damage if you get that wrong. I think it's pin 31 to ground. You should hear the relay click. You can also put an ohmeter across pins 31 and 87 when you do this, and that should read as open circuit when the relay is off and a few ohms when it's on.

In some relays you can measure the resistance across pins 31 and 15 but this doesn't tell you much i this relay as there's a resistor in parallel with the coil. However, if you open it up, disconnect the resistor and the diode, you should be able to measure a few 100 ohms across the coil. In my case the coil was gone.

You can also I gather connect the sockets corresponding to pins 31 and 87 together in the fuse box. This will manually connect up the power to the ABS ECU and if it is the relay that's at fault, your ABS warning light should not come on. I wasn't very happy doing this as I was worried the ABS ECU was a bit fragile and so I opted for just getting another relay. If you DO try this, I guess you will have to disconnect the jumper wire in the fuse box every time you stop the car or presumably the ECU will stay on all the time and drain the battery.

Good luck,
Chris

 

[gavinbray]

Right well so far today i have checked the ABS ecu connection and found it to be in good condition and dry.Also started the car up and checked for when ABS light comes on,i can confirm as i suspected that it comes on at start up and remains on,suggesting that the ecu has indeed gone,sounds simple? my parts chap has quoted me £35 incl post for an ECU,so just go buy?

No it's not that simple[] Now this is all thinking aloud and i do have a habbit of getting ahead of myself when it comes to thinking,but just as a fried ECU can make the ABS light stay on surely,a stuck relay can also cause this as Chris has said,i have kinda been here before. My former car of choice/play thing was old Rover SD1 V8s,so no such thing as ABS there however plenty of relays and the odd ECU. The car kept on braking down(well it was a Rover) would run fine for 100 miles,then just stop running,i was convinced ir was something to do with either main relay or pump relay,and indeed after fiddling about with them and changing to spares the car would fire up again,then die again a few miles down the road(i kid you not,happened 7 times from Luton to Surrey 1 day) but this turned out to be the ecu flooding the engine at a certain temp,the lesson i learnt there was a,i don't know what i'm doing and b,relays tend to be very reliable and rarely go south,old ECUs not so,dry joints etc.

Later on my friend and I will take the car out for a spin to skid test the car to see if the ABS is working,although if not working it could still be 1 of the 2!!

Now elsewhere on this forum i read about a chap who put his battery leads on the wrong way round,I will admit to doing this too,makes me sound a numpty i know but this is my first Porsche and i just wasn't expecting the positive lead to be black,i mean why would it? Now on his thread he is having the same ABS light problem,chaps have said he would have fried the ABS ECU,but he claims that the ABS is working fine so i just don't know where that leaves us.

This forum seems to have alot of members,surely someone on here has tech info and testing info for such things? Meanwhile Chris i have no such worries when it comes to replacing the relay with a direct connection to see if the light goes of,a relay is only a switch,isn't it?

Cheers Gav.

 

[gavinbray]

Ok so i tested the car to see if the ABS worked and it doesn't,so my findings are...

Light comes on at start up and stays on.
ABS doesn't work.
Replaced relay with jumper wire,light stayed on.

All of which would point to the ABS ecu being fried,so have just ordered a 2nd hand one,should be with me by Monday,i will test then.

Thank you for all your help so far.

Gav.

 

[deafasapost]

That'll be moi with the abs light on

tbh, i havnt had 5 mins to look at it with work, the little fella, and the house being all but inaccessible with the rip out and re-build.

as soon as the scaffolding is taken down so i can actually get the car out of the garage, i'll take a look at the fuses and the relay. let us know how you get on with the ecu tho, be interesting to know what your cars prob is.

 

[amrbose14]

Well I'm very rusty on this but...

Its a switch with a zener diode across it to limit the voltage supplied to the ECU to 12V. I don't quite get why this helps since the voltage is being switched on both parts of the circuit, but I think it's to help with voltage spikes - which presumably might fry an ECU on a bad day. There's also a resistor in parallel with the coil, which I believe prevents induction of currents in the circtuit it controls when the switch is going on and off. So there are some things in the relay to protect the ECU. I agree it's just a switch, but most electronics dies when you turn it on and off.

Of course, it didn't matter did it? You were fine. Keep us posted.

ORIGINAL: gavinbray

This forum seems to have alot of members,surely someone on here has tech info and testing info for such things? Meanwhile Chris i have no such worries when it comes to replacing the relay with a direct connection to see if the light goes of,a relay is only a switch,isn't it?

Cheers Gav.

 

[gavinbray]

Well from the info i have gathered on here(thanks again) it is pointing to the ecu going south,probably due to my battery lead mishap,will see what happens with the s/h ecu,if this doesn't work then it can only be the pump,or of course the relay could have gone too,or the s/h ecu i am waiting on could be shot[] oh the joys of DIY classics[&:]

 

[gavinbray]

Ok update time.You may recall that i did a crude test of the ABS system(slamming on the brakes to see if she skids) and i found that i didn't have ABS.Today i put on the 2nd hand ABS ecu i got last week,did the same test and it was VERY difficult to get the car to skid,i had 10 goes at this and only once did it skid at all and that was only slightly,so it would appear i now have ABS,however the ABS light is STILL on!!! I find this upsetting,why would the light still be on? is there any way of resetting this? please help!!

Cheers

Gavin.

 

[deafasapost]

hi matey,
i think you can disconnect the battery for 5 mins then reconnect to reset the ecu's.
i'd try this first as its the easiest to start with.

then look at the relay again and the sensors. other than that, i'm a bit stumped.

 

[gavinbray]

Hello mate,me too!! will try that but i don't hold much hope as the battery didn't go back on until after i changed the ECU. What needs pointing out here is this is a problem that appeared whilst the car is off road,yet after my mishap with the battery lead,so that mishap can only fry the ecu or relay right?

 

[deafasapost]

i think so. have you tried another relay?

either that, or as someone here pointed out, it could be that its on because its been left standing for a while, ie the brakes not getting any use.

when i can get mine out, i'm going to run it for a bit (every day if poss) and see if it rights itself through use.

if it doesnt. i'll check the relay and replace that and the abs ecu. other than that, i'll look at the sensors.

eeeee, the joys of cars eh [].

 

[deafasapost]

any update on this matey?

 

[chrisg]

I hope by now the various posters for this topic have fixed their ABS woes ?

Having had a non-functional ABS system on my '88 turbo which now works and tinkered a bit a couple of observations:

1. The easiest way to test the ABS (whilst working on the car with all 4 wheels of the deck, on axle stands) is to run the rear wheel, then stick it in neutral and hit the brakes. By default the front wheels are stationary, rear wheels moving - should produce a significant 'pumping' of the brake pedal as the ABS pump releases then reapplies the pressure to the front brakes.

2. The ABS system on the 944 is common to the 968 and 928 (hence why a lot of the parts start 928), there's a number of different ABS pumps and ECU's. ( I know from looking through 100's at PH Sportscars...) My understanding is they are matched and should be replaced like for like with the same Bosch and/or Porsche part number. Different version ECU's will probably fit and may work, different version pumps won't as the brake pipe orientation, including the rear bias valve is totally different.

As I explained to a couple of the chaps recently, the ECU and pump I have for sale I'll only sell to someone needing the same part numbers - waste of someone's time and money if their the wrong versions.

3. The system is very straightforward = Pump, ECU, Relay, Shared fuse, Sensors and wiring. The later element has a number of connections including 4 x earth leads from the cylindrical connectors. All of these, but in particular the rear ones are exposed to the elements and can fracture/ corrode very badly - good starting place

4. When my system failed, there was no dash light, Pump solenoid got stuck fried the ECU (as diagnosed by very helpful Bosch indie specialist nr Royston). My understanding is that when the dash light comes on = sensors, wiring or ECU ?

Yours, not expert by any means, but had a lot practice tinkering with 944's,


Chris