ABS hydraulic valve body resistor

[Roger Blassberg 0]

There's a socking great big resistor on the side of the ABS valve body. What is its function please, and what happens if its connections get dirty/corroded or the resistor itself develops a fault? What is the normal resistance?

 

This is actually a question relating to my Passat B4 (LHD) which has a persistent ABS warning light malfunction, but Passat Forum lads have not come up with a solution .

 

Most of the time it works as it should (goes through light on / light off sequence on startup) but occasionally the light comes on after turning the steering hard to full lock one side or the other at slow speed. Light then goes through on/off sequence after restarting but comes on at about 10mph. If left overnight, it sorts itself out. New front sensors, new front cables from sensors to inside, replacement ABS ECU.

 

1551 shows an intermittent pump malfunction. I have just changed the brake fluid to no effect.

 

Trying to avoid changing the valve block/pump, so doing "cheap" fixes first.

 

Best wishes

 

RB

[RW1 0]

The big resistor is not directly the ABS. Its part of the Electronic Diff Lock (EDL) or Traction Control System (TCS) as VW UK decided to rename the function.

 

The resistor is a drop down voltage resistance to run the ABS motor at a slower speed and therefore lower hydraulic pressure when EDL is engaged due to a wheel spinning/slipping when intially driving off upto 25mph approx.

 

If the resistor is fitted, then the ABS valve block has two additional valve ports (totalling 6 instead of 4). The additional two valves are in the dual circuits going the rear brake pipes/brakes to cut off hydraulic pressure to them when EDL operates. That then allows the EDL to use the front ABS valves to control the two front wheels hydraulic brake circuits individually with use of hydraulic pressure the ABS pump provides.

 

Nothing happens unless one or both the two front ABS sensors detect a wheel is slipping. At the occurrance, the slipping wheel is braked (not locked) by the slow running pump pressure forcing the drive to be taken up by the other wheel through the gearbox's mechanical differential. When it detects the wheel is gripping again, the ABS valve block releases the brake pad pressure to allow the wheel to drive again.

 

After starting to move, at 25mph the EDL becomes inhibited by the ABS ECU. It also doesn't really operate unless the steering wheel is set between 10'o clock and 2'o clock. Outside these boundaries either side, wheel spin still occurs.

 

If the connections become poor for the resistor, the EDL will have no hydraulic pressure to work with, as the pump won't be spinning. Some resistance means a slower running pump and less pressure than normally available. So the ABS ECU may operate the ABS valve block valves, but the front brake pads will not grip the brake discs enough to make EDL work efficiently.

 

The resistor being higher resistance through bad connections will not stop the braking ABS circuits working properly. That voltage to the ABS pump is fed via a separate circuit path.

 

.

Edited February 7, 2012 by RW1

[Roger Blassberg 0]

Thanks RW1 for your usual very high standard of response - I almost knew from the outset that it would be you who would reply to this topic.

 

My thinking on this problem is as follows;

 

The fault only seems to occur after a slow tight manoeuvring turn, below the 25mph EDS/EDL/TCS inhibition speed, so maybe it is indeed linked to that function and this is causing the pump to operate in such a way that it flags up a fault. I am confident that the front sensors and cables have been ruled out as the culprits, and the gaps (sensor/slotted hub ring) are within tolerance

 

Does the fact that the fault clears after leaving the ignition switched off (eg overnight ) give you a clue to the underlying cause?

 

I'll clean the contacts to the resistor - do you happen to know the design resistance value?

 

Thanks and best wishes

 

RB

[RW1 0]

I will have a hunt round for the resistor value. It will be low in value being wire wound and its size. Its in series with the pump motor when engaged by a relay.

 

Would help if you stated which fault codes you seeing.

 

.

[Roger Blassberg 0]

Thanks again .

 

I'll get the code from the report.

 

Any idea where the relay is that engages the resistor - in the ABS ECU perhaps?

 

Best wishes

 

RB

[Jon_vr6 1]

Im sure theres abs relays up behind the glovebox?

[Roger Blassberg 0]

Thanks Jon vr6.

 

Don't forget that the car in question is, in fact, a Passat B4 (a sneaky interloper in this esteemed company.....) but maybe similarly laid out. The glovebox is occupied by an airbag in this case.

[RW1 0]

Resistor is 0.66 ohms, +/- 5%. Upper permitted resistance from the connection plug by the ABS motor is 2 ohms.

 

Relays (3 off) are above the fuse relay plate. One is the EDL, it is the only relay of the three with 4 wires, the other 2 have 5 wires for one relay, 6 wires for the other relay to the base mounting. (Double brown counts as one)

 

Fault codes???

 

.

Edited February 12, 2012 by RW1

[Roger Blassberg 0]

Fault codes (at last !!)are;

 

00276-035 ABS outlet valve rear left -N136

01276-016 ABS Hydraulic pump-V64-signal outside tolerance.

 

I have found a second hand pump/valve block/mastercylinder/servo on ebay.de from a B4 VR6, just in case the worst happens. Does anyone know if all VR6 setups included traction control (LHD remember)?

 

But obviously I want to make sure that it is not an in-car electrical fault first.

 

Your continued help is appreciated.

 

RB

[RW1 0]

Yes they do, recognised by 6 hydraulic outlets for EDL enhanced, not 4, on the valve block.

 

Not an EDL problem!

 

00276 = internal Valve Block problem with rear left ABS valve.

 

01276 = ABS relay (one with 5 wire conections [3 of which could be dual into the base pin, same colour] to the base) or the ABS pump or the ABS pump sender inside the pump.

 

Also, really clean the ABS electrical connector pins/sockets to remove any dirt. Use WD40.

 

.

Edited February 11, 2012 by RW1

[Roger Blassberg 0]

Thanks

 

Can't find the ABS relays !! Sounds daft, took off the fusebox cover, and also the undertray into which that fits and exposed all electrical wiring around the fuse box. (LHD remember.) Only the relay positions 1-12 apparent. So took off undertray on passenger side, not there. Corrado Bentley manual (wiring diagram 84)shows abs relays in positions 13 (relay 78) and 14 (relay 79) and fuses in 19, 20 but of course this is a Passat B4. Are relays 78 and 79 the ones i'm looking for, irrespective of their position on the board?

Will clean connectors as directed but have done so once with contact cleaner; but a bit suspicious of the valve fault, sounds hydraulic rather than electrical and may be beyond easy repair.

 

Again many thanks for your support. Mrs B has just come in and reported that no unusual warning lights are showing at the moment so it is VERY frustrating.

 

RB

[RW1 0]

I'd expect them to be up above the fuse relay plate by the bottom corner of the A pillar/windscreen corner.

 

Words from the Passat 1994 VW manual are "Above the relay plate" for all three relays.

 

So even look inside the dash inside lip behind the lights switch.

 

If the valve is faulty ie wiring to it or the actuating coil is open circuit, it may be causing hydraulic pressure problems. And hence why the pump is seeing pressure problems with 01276 fault code.

 

.

[Roger Blassberg 0]

I took out the headlight switch and had a good peer around that area and coiuldn't find those wretched relays.

 

However, I once again disconnected the multi-pin connector on the ABS unit and gave the pins and socket a good clean with WD40 as suggested. I also noticed, (for the first time it must be added,) another 2 connectors. One is further down behing the multi-pin and has two fairly thick red/stripe wires - I assume to be the main power supply to the unit, and also a two wire connector to the pedal position sensor on the servo unit. I disconnected and cleaned both of these then re-assembled.

 

A good drive around, including all the usual manoeuvres which have in the past brought the fault light on, has so far NOT brought the light on.

 

Best wishes

 

RB

[RW1 0]

Lets hope that bottoms it :)

 

For the record, these are the ABS & EDL relays and their position on the Passat. Puzzling yours is different.

 

[ATTACH=CONFIG]51961[/ATTACH]

 

.

[Roger Blassberg 0]

Thanks for all your effort.

 

They are too big to miss seeing aren't they?

 

As said, this is a LHD car built in March 1994 and I've had it since new. The main fusebox was replaced a while ago, but obviously those relays and fuses for the ABS must be somewhere. Fingers crossed that this has cured the problem, but my curiosity is now aroused and I want to find those relays. I have tried locating them by listening out for the click as they go through the initial ignition-on check, but so far unsuccessfully.

 

Best wishes

 

RB

[andrewchapple 0]

Roger, have a look under the back seat as I have seen some there on some models.

[Roger Blassberg 0]

Found the relays at last - they were hidden behind the main fuse/relay board. I changed the no. 79 and no. 179, but STILL have the problem. I think it must be the pump/valve block because I have now changed just about everything else.

 

Someone has suggested that there may be an interference between the wiring to the pump and the engine speed sensor/ignition wiring - a current being induced from one to the other due to their being in close proximity to each other, causing a fault to show up. Anyone heard of this before?

 

Thanks for continued interest.

 

RB

[RW1 0]

So they didn't put the relays back into position when the relay/fuse plate was changed :)

 

Interference - Clutching at straws with the wiring picking up interference. Carries only 12 volt on/off signals or current supply 12 volts. Not likely.

 

Those fault codes point to an internal valve block problem if its not the connections.

 

.

[Roger Blassberg 0]

RW1 - not quite that. There is a plate, right up high, fixed to the firewall,which supports the 79, 179 and (2 off) 53 relays. They had been obscured from view until I unclipped and dropped the main fuse/relay board. So, no bad workmanship, just an arrangement different to that you and I expected.

 

Anyway, having replaced 79 and 179 no change to the problem; what do the nearby 53 relays do??

 

If the car is left for several hours, all works perfectly well from startup UNTIL the ignition is switched off. If it is restarted fairly soon afterwards, the on/off test sequence works on startup, but the light comes on again at about 10mph and stays on until ignition switched off. Leave it overnight and all is well again until the next time. Sounds like a lazy solenoid or sticky valve. I have now found a place in Kent (BBE Reman) 01634 687222, who can rebuild the pump/valve block for about £150 with a lifetime guarantee, turnaround in 3 days. This looks to be the way to go. I have also found a replacement (2nd hand) part, a complete servo/mastercylinder/pump/valve block on ebay.de which I may go for if the price stays reasonable.

 

RB

[Roger Blassberg 0]

Latest news on this.

 

I took off the heat shield from the side of the ABS unit so that I could see the part number. By then it was getting dark so I left the shield off.

Next day I had a long journey, so I drove 300 miles without the heat shield, and Lo! and Behold! the warning light is doing exactly what it should.

 

Could it be that the extra heat on the unit has somehow dried out some moisture in the wiring or has coaxed the pump back into action??

 

Anyway, I have now bought a secondhand unit from ebay.de as a strategic reserve in case of a recurrence of the problem, and will keep my fingers crossed. In the meantime, we have sailed through the MOT test without so much as an advisory so we live to fight another day!

 

Best wishes

 

RB