I’m about to dive into the user manual and try to understand the ABS system, but any hints and tips are more than welcome.

When I turn the car on, there’s no ABS “Anti Lock” light, but as soon as I brake moderately, it goes on. Then off again when I start the vehicle again.

Any thoughts on what’s going on? Just after a head start on the fault finding. Most of the posts I’ve read imply it’s on solid right from ignition, so thought this might be something different.

Car is a ‘94 XJS, with the AJ16 engine.

 

N Bath,

Turn off the ignition, press the brake pedal repeatedly (25 times). It should get harder and harder. Now turn on the ignition to Pos 2. The light should come on and the ABS should start to run for about 40 seconds. The pump should then cut out and the light will go off. Does this happen.

Paul

 

Thanks, here’s what happened:

1) Key in position 0, Pressed brake pedal 25 times.
2) Turned key to position 2.
-Anti Lock light went on briefly, perhaps a second, then off.

3) after that, key still in position 2, I pressed the brake pedal to the floor
-Anti Lock light went on, audible rattle/humm, light went off after 3-4 seconds (much longer than in step 2).

Step 3 was repeatable.

 

1. Did the pedal get harder and harder when you pressed the pedal 25 times with ignition off? (To the point of being almost rock hard)

2. Did the ABS pump start running when you then turned the ignition to Pos 2? How long did it run for before cutting out? (Don't touch the pedal during this)

3. IF the pump runs for 25+ seconds before cutting out, THEN press the brake pedal for no more than 2 seconds. What does the pedal feel like? Has it moved to a more normal feel than the rock hard feel in Step 1?

Paul

 

Thanks again Paul:

1. Did the pedal get harder and harder when you pressed the pedal 25 times with ignition off? (To the point of being almost rock hard) - No, it did not.

2. Did the ABS pump start running when you then turned the ignition to Pos 2? How long did it run for before cutting out? (Don't touch the pedal during this) - hard to know, but there was an auditable buzz/hum for less than a second, similar to that of Step 3 above. I can double check this if it’s helpful.

3. IF the pump runs for 25+ seconds before cutting out, THEN press the brake pedal for no more than 2 seconds. What does the pedal feel like? Has it moved to a more normal feel than the rock hard feel in Step 1?

I don’t think it is running for that amount of time. If it’s the hum I’m hearing in step 3 above, it’s only on for a few seconds.

I can try again and put my hand on the pump, but I think from the sound, it’s only running for 3-4 seconds.

 

N Bath,

First of all, when did this problem start? Is it recent, and have you noticed a very distinctive difference in the feel of the brake pedal when driving?

Apols if you already know all of this but just to clarify:

When the ignition is turned on, normally BOTH brake warning lights would come on - The Red brake light plus the Amber ABS light. The pump will then run until it has charged the accumulator. A pressure switch tells it when to cut out and then both lights will extinguish. Sometimes the Amber ABS light will stay on for a few seconds until you've moved and then it will turn off. If the accumulator wasn't charging, the pedal would be so hard as to make the car almost undriveable.

When driving, the brake pedal has a slight softness when pressed because of the boost effect of the pressure stored in the accumulator.

If you turn the ignition off and repeatedly press the brake pedal, you will use up the stored accumulator pressure. Therefore the pedal will get harder until there is almost no free travel at all. I'm confused as to why that pedal isn't getting harder after just a couple of presses when the ignition is off?

The reason that I suggested doing the repeated pedal press with the ignition off is to use up the accumulated pressure, such that when you turn on the ignition, the pump will have to run for some time to build up the requisite pressure. In all Teves XJSs that I have seen, the pump buzzing is really quite audible from inside the car. So, if the pump isn't running (failed pump or faulty pressure switch) then the brake pedal would be really hard in normal driving.

However, if the pump isn't running, you should also get the red brake light coming on / staying on as it monitors the boost pressure. If you haven't got that light coming on, it IMPLIES that the boost pressure is ok. (But I find that strange if you've pressed the brake pedal 25 times and then the pump doesn't run after the ignition is turned on?)

The Amber light will come on when driving if the system spots a fault with the electronic ABS side of the brakes. So if you had a pressure problem, the Red light should come on, then the amber light would also come on as it realises that it can't apply ABS if the pressure is low.


Let's start the routine again:

Have the car running for a minute. Presumably all the brake lights are out? Press the brake pedal. Does it feel "normal"? Release the brake pedal. Turn off the ignition.
Press the brake pedal a few times quite firmly. The pedal should start to get much harder to press as it uses up the assisted boost pressure. Does this happen? Press the brake pedal 25 times to ensure all stored pressure is dissipated. Release the brake pedal.
Turn on the ignition. Which of the 2 brake lights come on? Can you hear the pump running? If either of the brake lights have come on (I'm expecting both), how long before the pump cuts out and the lights go off? Press the brake pedal. Does the pedal feel "normal"?

Paul

 

Thanks Paul, really appreciate the help, I’ll try those things and get back to you.

I noticed the Anti Lock light on the way to the mechanic. The car needed new rotors and pads (hence the trip to the mechanic). The mechanic replaced all the rotors and pads, and bled the brakes but the ABS light wasn’t resolved (stupidly, I hadn’t mentioned it to the mechanic). But I’m keen to try and resolve this one myself (with help from the forum) if I can.

The brakes feel really good to drive.

 

OK, so some work has been done on teh brakes, but the problem was there beforehand.

Would your mechanic understand the Teves II system? For example, the rear brakes have to bled in a different way to a normal car. Also, there some No-No things that should be avoided, such as pushing back the pads and caliper pistons without first undoing the caliper bleed nipple, as otherwise it can push sediment back to the ABS valve block.

However, notwithstanding all of that, I'm still confused as to why the pump doesn't seem to be running, and why the pedal isn't getting hard when the accumulated pressure is dissipated. I'll wait to see how you get on.

Paul

 

Sorry, really quick question: Your 1994-built car with the AJ16 engine - your VIN is earlier than 198335, isn't it?

Paul

 

Yes it is.

 

Hi N Bath

Is your Brake Reservoir Square or Triangular?

 

It’s square-ish.

Photo attached.

 

Hi N Bath

You've got the Teves 11 Master Cylinder Actuator

There are many Shops and Mechanics out there who have never worked on an XJS and know nothing about the Teves Braking System

Its Nothing like on a Normal Car and as Paul (ptjs) has pointed out 'Pushing Back the Brake Pads' like many of us do on Normal Cars, is an Absolute NO NO! on the Teves Braking System, for all the reasons Paul (ptjs) has alluded to

Where doing any of the things that Paul (ptjs) has mentioned, can damage the Components in the Valve Block that is Bolted on the Side of it, where an ingress of 'Crud' could easily cause one of the Valves in the Valve Block to Stick open

(1) Open the Fuse Panel on the Passenger Side (the knee high fuse Box Panel) where inside you should see 2 X 30 AMP Green Blade Fuses

One is for the ABS and the other is for the Brake Pump (They are Clearly Marked which one is which) You want to be looking at the ABS one

Pull out this ABS Fuse and not only Test it but examine the Blades as well as the Fuse Holder for any signs of Corrosion

It could very easily be as Simple as a Corroded or Blown Fuse, which would cause the ABS Light to Flicker or Come on

Since they are as Cheap as Chips Replace the Fuse with a New One

Or it could be a Wheel Speed Sensor that may have got broken when replacing the Caliper or still needs to be Connected

So how come the Car apparently Still has Brakes?

Well believe it or Not you can Still have Brakes even though the ABS isn't working! (although they very obviously won't be ABS Brakes) until the problem is Fixed

In which case if you have an Accident, your Insurance Company may just decide to disown you! so best to have it working properly

Try the Fuse thing First and see how that goes before we did any deeper

Then Paul (ptjs) will be able to talk you through 'The Blink Test' if that doesn't work

 

N Bath,

Before you check anything else, we have to get to the bottom of the original test, which seems quite confusing.

An XJS with the Teves II system is almost impossible to drive without accumulator pressure assistance, It's like trying to drive a car with the servo disconnected on the brakes. The pedal would require really heavy pressure to get the car to slow down.

So, if your car is driving normally as you mentioned, then the pump and accumulator must be working. But if that is the case, when you press the pedal repeatedly with the ignition turned off, you WILL lose all the accumulated pressure assistance. And the pedal MUST get much harder to press. The only way that I can think that the pedal wouldn't go very hard is if you had a lot of air trapped in the system. But even then, the pedal would still be harder than normal, after you've dissipated the accumulated pressure.

So, we have to get to the bottom of this issue, before we can go any further, or test anything else.

I hope that makes sense.

Cheers

Paul

 

I’m following this with interest as I have an anti lock light now on permanently after it came on intermittently following a front caliper rebuild and fluid flush. Both front ABS sensors removed, cleaned and tested and ABS rings checked.