Roy LaZelle

I am a 944 owner, however as I understand it 928's and 944's share the same ABS system. Additionally, I found the most ABS questions and answers in the 928 forum. In my 89 944 S2, the ABS warning light now lights up when I start the car. I have checked the forums and found a bit of information. Apparently there are two checks:
(1) there is a self check when the car is started
(2) a sensor check after the car starts moving.
So, it looks like my problem is in the self check. There were also some posts suggesting that relays could also cause this. After looking at the circuit diagram for the ABS (section 45 page 04 of the manuals) in case the relay was bad, I pulled the ABS relay and jumped terminals 87 to 30 while the car was idling. It should have powered up the ABS and turned the light off... which it didn't. There are two more relays on the ABS Hydraulic unit, in the right fender, which I will check next weekend.

Could a broken sensor wire cause the self check to fail or are my problems limited to the Hydraulic unit and it’s power.
How about the testing unit a Bosch K7-ETT 016.00/VAG 1516 mentioned in the manual are those at the dealer only ??
Suggestions anyone ??? --Roy--

Randy V

Once the ABS light is activated, it can only be reset using the Bosch multi-tester (aka Bosch Hammer).

I suggest having the ABS reset by your mechanic or Porsche dealer. If the warning light comes back, then you know it is a recurring problem rather than an anomoly and can then begin troubleshooting.

FlyingDog

Randy, what do we do if we have a pre-Hammer ABS car? What about a pre-ABS light ABS car?

Warren928

My ABS light has come on just from driving its first 80 feet of the day on a sandy gravel driveway, my accounting to this is that the brakes are locking up on the driveway and causing a false ABS code being generated. I will shut the car off, restart it on the paved road and the fault light is gone.

As far as the self check goes, can you get a code from the car to narrow the problem down? Is it acting abnormally in any way when braking? Do the wheels lock up under a brake check?

IcemanG17

My ABS light would come on intermittently for a while...typically when starting....so I would do the "windows fix" of turn it off-start again and usually it would go away...then one time when driving, I hit the brakes pretty hard and it came on with the warning light & stayed on. Turns out the relay on the fuse panel was bad....quick and easy fix!

Jim M.

The ABS light (at least on a 928) does not require the hammer to reset it. I think Randy is thinking of the air bag light. Most likly a relay problem. The system is very reliable, if the ABS goes off due to a system failure, braking reverts to non-ABS braking. There are several reasons for an ABS warning light. It can be corrosion at connection points, a bad relay 928 615 124 01 on the fuse panel. Using an insulated jumper wire you can bypass the relay by plugging two spade terminals into the slots on the relay board, that correspond to pins 30-87. Be sure to identify the correct slots. Open or short circuits in the speed sensors, speed sensors that have too much metallic crud in them or on the tone ring. To be functional the ABS needs to know the speed of each wheel so if any of the sensors, connections or wires fails it shuts off and triggers the warning light. The sensors are A/C voltage generators that create a sine wave output, usually somewhere around +/- 1 or 2 volts, when the teeth of the sensor ring pass the sensor. There are two electrical tests for the sensors; a continuity test with an Ohmmeter, and a comparison of the sine waves with a scope. The problem is much more likely to be faulty connections than faulty sensors. The ABS control module compares the sine waves to see if a wheel is locking. Malfunction in the ABS valve body. The ABS light should come on when starting and go off after the few seconds of self-testing. If the ABS light stays on then it’s more likely a hardware failure than a signal loss from a sensor. Start with the ABS relay. If the light goes off, but lights again within a few moments of moving off, it indicates a sensor which passes the start-up test is now failing to send an adequate signal. If ABS warning comes on after car is in motion, then there's a differential/non signal sent to the ABS brain so the sensors/connectors may be the problem. Check the sensor connections at the wheels, a black 2" long cylinder. This could be dirt in the ABS sensor area or a flaky connection. They get loose or installed in the wrong hole (3 holes, wear sensor, ABS, and RDK). Inspect the cables for deterioration and shorts from the connector to the chassis. While the ABS light stays on, the ABS module is not operating at all, but normal brake pressure will still be applied from the brake pedal. There are two relays mounted on top of the ABS unit in the LH front fender, under a cover, behind the splash shield, partially visible from under the hood, near the power steering reservoir. The system goes active at about 35 mph. The ABS control module needs to see relatively clean pulse signals from each of the sensors. If the signal from one wheel drops out, the system will turn on the ABS light and the system will shut down. Removing ABS relay will disable ABS circuit; I drove like that with no brake loss, waiting on my new relay.

Jim Mayzurk
93 GTS 5-spd

Roy LaZelle

Thanks sharks for all the replys. My question is generating more interest in the 928 forum than the 944 forum, as in 5 messages here to 1 there.
(1) On the fault code front, I checked PET and the 89-928 ABS controller has the same part number as my 89-944-S2. So, perhaps the same fault codes are available. I sent an e-mail to JDS in England inquiring about reading the fault codes with "The Spanner". I also did a search for ABS in the pdf copy of "The Spanner" users manual and it says there that it will read and display 15 ABS fault codes. I would like a little more encouragement for my 944 before forking out $700 for the code reader and cable, hopefully the e-mail will do that.
(2) on the relay front. I did jump 15 to 30 in the fuse/relay box, while the motor was running,without any change in the ABS light. So my question in that area is, would a broken sensor/wire/plug cause the ABS light to come on during the self check, prior to moving the car. My weekend plans are to pull the fender splash guard and verify the ground and other connections.
Again thanks for the help. --Roy--

FlyingDog

Roy, there's probably someone fairly local with a Spanner. Maybe Heinrich can point you to a Seattle Spanner owner. If not, I'd assume Louis Ott has one and I think he's near Portland.

Randy V

Jim got me on that one - he's absolutely correct - my previous problem was an airbag fault light, not ABS. Apologies for the incorrect advice.

John Speake

Hi Roy,
I did answer you first e-mail, but judging by the one you sent today my reply didn't get through.

If you still haven't received either of my two mails, then please PM

Regards

Roy LaZelle

John:
I received your second e-mail to my home address (but not the first obviously) to my work address.
So if you received my reply, it looks like we have a two way connection to my home e-mail address.
--Roy--

John Speake

OK Roy,
I will reply to you there....

WallyP

Connecting terminal 15 (switched 12 vdc) to terminal 30 (constant 12 vdc) won't have any effect other than powering the switched bus with the ignition switch off.

John Speake

Hi Roy
You should be able to cancel any stored fault code in the ABS ECU with a battery disconnect.

The most common cause of ABS fault codes is faulty ABS sensors in the wheel hubs. They corrode- this crushes them so they don't work.

littleball_s4

Hi,

Roy, I hope you already found the problem.

I've just discovered a bad main ABS relay in my s4. I've jumpered 30-87 and then started the engine. It works. (Light went instantly off as soon as the engine roared and anti lock effect is back). I think you don't even need to unplug the batery to reset abs light off.

A couple of newbie questions for you:

What's the relay for? When I jumpered it I heard nothing (it was a quiet place). Will it drain my batery dead if I keep it jumpered?

Can I pry it open? I'd better go buy a new one?

Many thanks!