Abs ecu

[Roger Blassberg 0]

Happy New Year to all.

I am having ABS problems. The warning light does all the right things when starting from cold (on then off, stays off after test cycle a few metres down the road), but after a warm start it comes on after the test cycle. The next day, this sequence repeats itself.

 

All three ABS relays, 2/179 and 1/79, are functioning and the 2/ 30A fuses are good. We have interogated the inner soul of the ECU and it brings up a fault on the pedal position sensor. So I have replaced that with a spare one after checking that the variable resistance, err, varies, and that the colour coded spacer is correct. Still the same problem. (By the way, getting the circlip out is best left to a gynaecologist)

 

The ECU , part nr 1HO 907 379C seems clean and dry with no obvious corrosion inside or out or on the 55 pin connector.

 

But I am tempted to try a spare ECU from my B4 Passat, part nr. 1HO 907 379E.

 

Both ECUs are for ABS/EDS.

 

Does anyone know if the Passat ECU is compatible despite different part nr. suffix letter.

 

Any observations and suggestions are welcome.

 

best wishes,

 

RB

[seanl82 23]

Roger,

 

When I was having problems with mine I tried a replacement ECU with a different suffix. After fixing the problem which turned out to be the PPS I tried the ECUs again and they both operated correctly. I can't remember what the suffix's were, but I think they're interchangeable.

[Roger Blassberg 0]

Thanks for your quick response Sean. I will try the substitute ECU tomorrow and take it from there.

 

I am sure it can do no damage if it is not fully compatible.

 

Any further comments about the underlying fault and its possible causes are greatly welcomed.

 

best wishes

 

RB

[fendervg 32]

My guess would be a damaged circuit board on the ABS pump unit - this is underneath the pump and gets dirty and can also crack, maybe expanding with engine heat when warmed up, causing the light to go on when the engine is warm. Only solution is a a replacement or refurbished ABS unit - that's what I eventually did on mine having had similar issues and having checked all the other (cheaper) components were ok. You could always try removing the ABS unit and then seeing if you can get access to the PCB by removing the two long hex head bolts to check it's condition and the state of the soldered joints. I haven't been able to do this with my old one yet as one of the bolts has rounded off.

[Roger Blassberg 0]

Thanks Fendervg. I am coming to the same conclusion myself. I will replace all the relays, maybe one or more of them is suffering similar heat/ pcb problems. I will also do a complete fluid flush as I had a caliper changed very recently so there may be some sludge that has been moved about in the pump or valves . Latest analysis is of pump signal out of tolerance.

 

Failing that it is a trip down to BBA REMAN in Rochester to have my credit card assaulted.

 

best wishes

 

RB

[Roger Blassberg 0]

I have now replaced the relays and the problem persists with either ecu. So it would seem to be the pump unit that is faulty. Additionally, the light comes back on after a few metres down the road irrespective of whether the engine compartment is cold or hot, so the cause of the fault is apparently getting more severe. It does point to a possible electrical/electronic failure.

 

Before I throw it at BBA REMAN, does anyone here have an opinion on them? I have seen negative comments elsewhere, and good comments on ECU TESTING in Derbyshire. Both are quoting similar charges to sort it out, so I am interested to know what you may think about either or both of them.

 

best wishes

 

RB

[marks2 0]

I have an ATE ECU p/n 1H0 907 379 that I know works.

 

If it's the same as yours you can borrow it to check your system.

[seanl82 23]

The system does a self check at start up so if it doesn't come on initially the the valves are probably ok. The actual circuit starts reading wheel rotation from around 15mph - which suggests it's something to do with the sensors, reluctor rings, or the loom itself. You're honestly best off getting the codes read. Even with the early 2x2 diagnostic ports, a £2.50 adapter will enable a modern obd reader to give you the correct codes and point you in the right direction.

[seanl82 23]

Sorry, forgot you had already read the codes! I was getting confused with another thread I think! Have you cleared them then read again to see if there are any additional codes?

[Roger Blassberg 0]

Thanks Sean. Yes I have, the pedal position sensor is now ok, just the pump signal is out of tolerance.

 

best wishes

 

RB

[Roger Blassberg 0]

I eventually replaced the pump/valve unit with a known good second hand unit and all is well again. Incidentally, it took a lot of time and effort to get a decently hard brake pedal after the change, but we got there eventually. The trouble is that I get used to the very powerful brakes on the B6 Passat, and then the Corrado brakes seem so soft and weak.

 

Best wishes

 

RB

[Roger Blassberg 0]

To be honest I am still not happy with the brakes......weak and very long pedal travel.

And.....

When I switch off the engine with my foot on the brake pedal, it immediately kicks back and loses all vacuum assistance. Is this a leak in the servo or the associated hoses? I have a spare non-return valve, I will try that tomorrow. Maybe the pedal position sensor grommet didn't seal properly when I replaced the PPS and is leaking to atmosphere.

All comments gratefully received.

 

Best wishes

 

RB

[fla 9]

Hi Roger, it took a while for my brakes to get the proper feel back after bleeding them, i wonder it its just a question of time? Not sure about teh vacuum loss, though it does point to a leak somewhere, hopefully not the servo..

[Dox 23]

I had a similar issue with my golf losing vacuum with the ignition off, the mani to servo pipe had split.

 

I opened all the abs pump connections in turn to bleed the pump itself using a pressure bleeder, the two man method would also work.

 

You could also wedge the pedal down overnight before rebleeding, some say it helps to move stubborn trapped air.

[Roger Blassberg 0]

I finally sorted the weak braking effort down to an air leak into the low pressure side of the servo, so that there was really practically no assistance. When replacing the pedal position sensor I had not replaced the O ring seal between the sensor and the servo body. Very embarrassing negligence on my part which caused a few heart-stopping moments and could have had tragic results.

 

All fine now, although still not up to the modern standard of braking I get used to inthe Passat.

 

Thanks for all interest and help.

 

Besr wishes

 

RB

[seanl82 23]

:bonk:

[fendervg 32]

At least it's sorted now.

 

Roger, how did you identify the vacuum leak and which hose was it?

[Roger Blassberg 0]

I disconnected the servo hose at the inlet manifold connection, and sucked on it!! It was passing air so I knew that either the hose or the servo was not airtight. Then I noticed that the PPS was loose in its grommet/seal on the body of the servo so I removed the circlip and took it out. The rubber o ring was missing due to total error on my part. After replacing it there is complete airtightness and the brakes are back to their former " glory". Good, although not up to modern standards. For a while I was afraid to drive it. The brakes were very hard and yet weak.

Best wishes

 

RB

[fendervg 32]

Thanks for the reply Roger - I will give this a try - I suspect I might not be getting full servo assist, or possibly have a weeping seal in the master cylinder, so this will help with my investigations.