I know that a bad ABS module does NOT effect the normal non-ABS brake function, but if I have to remove the module for repair/replace does that have any effect on the normal operation of the brake system?

 

I'm almost positive it will result in having no brakes at all. The brake fluid will escape from the open brake lines under relatively high pressure. Not good for paint.

 

I'm not asking about the ABS pump but the electronic control module that regulates the pump. I know you can lose the module and still have brakes since all you lose is the ABS function. I'm unsure about what happens when you disconnect the module. As far as I can tell there is no 'mechanical' connection to the brake lines themselves.

 

My GUESS is, the brakes would still work, but i'm not positive about it.

 

A bunch of signals are supplied to other modules from the ABS modules
The most important of which are the wheel speeds.

So for starters, no speedo, traction control, cruise control

Id also expect the instrument cluster to light up with every fault. AKA Christmas tree fault

There is a TSB on this which relates to a faulty pin on the SCP bus at the ABS module. When the ABS does not send data the instrument cluster lights up like a "Christmas tree"

You can always unplug the ABS harness and try for yourself.

Cheers
34by151

 

The only lights I'm getting are the ABS and DSC plus check engine (which is just to catch your eye in case you think the other two are mistaken for operational I's guess).

Yes the cruise control went away since it can't read wheel speed. What's got me is that I get no codes with the SDD. I'm going to probably try to remove the control module and take a look inside for any burnt/broken printed circuitry but if it's more than I want to tackle myself I'd have to send it to California for repair. That's the one my wife drives and uses every day so it would be critical if the brakes wouldn't work at all with the module attached.

Apparently mine is somehow different in that I still have a functioning speedo.

As is the car brakes fine excepting of course there's no ABS, etc. but we drove for decades without ABS so we can easily weather a couple of weeks without it.

 

Good to know for sure. One thinks something should logically work in a particular way, is WAY off the mark on occasion.

 

My mistake there on the speedo, the info comes from the TCM not the DSC

IF you recheck SDD, in the modules scan, you will find the DSC is marked as fitted but not functioning.
Also check the unrelated faults in SDD you should find codes P1799 and/or P1637

P1799 "CAN TCM / DSCM network malfunction", "Substitute transmission output speed for DSC vehicle speed"
This does not generate a MIL

P1637 "CAN ECM to DSCM network malfunction", "CAN open circuit fault – DSCM to ECM"

Actions
– Speed control inhibited
– Maximum throttle opening for N range inhibited
– Throttle opening limited to 30%
– Maximum engine speed reduced

This generates a MIL (check engine) after 2 drive cycles

Cheers
34by151

 

I had the same problem back in April, narrowed it down to dirty wheel speed sensors. Cleaned all four and have had no problems (lights on dash) since.

 

The wheel speed sensors were the first thing I checked. From there the list of possibilities multiplies like rabbits and I don't have the time to go through the list one at a time given 51 possible codes and 30 pages of pinpoint test instructions. At least no yet.
What's got me is that my normally reliable SDD program is giving me NO CODES.

Not a single one. NADA, nothing, zippo, zero. Not even a P1000 not ready fro prime time code.

 

The ABS modules gets it's data from the wheel speed sensors or from other points along that data channel. Lost ABS, for whatever reason, and you lose DSC since without an functioning ABS system you can't have directional stability control. You lose cruise control as well since it doesn't know what speed you're going. Why I didn't lose the speedo is a mystery but perhaps that function was still separate in the 2004 XJ's.

In any case my SDD programs has either gone nuts (or perhaps I have) or something else is amiss since I get absolutely NO CODES about anything and it tells my (by way of a check mark) that the ABS system is functioning and communicating despite the lights telling me otherwise and a CC that isn't functioning as well.

 

The speedo gets its data from the TCM (gearbox) and is calculated from the driveshaft rotations not the ABS wheel sensors

If the TCM is not supplying data it will revert to the DSC signals with the code P1799

Cheers
34by151

 

If I understand RD's question, he's asking about removing the electromechanical ABS module, not the hydraulic ABS modulator. The two devices are physically attached to one another, but the module can be detached and removed without disconnecting the modulator from the hydraulic lines. The module is the component that most often requires repair (typically due to cracked or starved solder joints on the circuit board).

The short pipes around the valves in the modulator are sealed, so when the module is removed no fluid is lost, and normal (non-ABS) brake function is retained. This is the fail-safe status of the system in the event of ABS failure.

The solenoids in the module control the valves in the modulator via electromagnetic coupling, so none of the components of the module is ever in contact with the brake fluid.

Cheers,

Don