HELP... 91' 164 ABS problems

["Keith Christoffers" <christkh@domain.elided>]

In AD V7 #501, Keith Christoffers wrote:

>I'm having difficulties with the ABS in my 91' 164L
>automatic. When I start the car the ABS light is not on.
...
> What could this be? (tell me it's not the hydraulic unit)

You should be more specific about the initial conditions. Insert
the key and turn it into OPERATING position, not into STARTING
position. After self test of the control panel only two control
light should remain ON, namely oil pressure and ABS system. 

Few seconds (2-3) after starting the engine, both lights should
turn off (oil pressure rises and ABS self-test is completed
successfully).

(BTW, at the engine start also self test of the adaptive suspension
(if there) is done - the red LED diode (under SPORT AUTO buttons)
should turn on for 2-3 seconds and then turn off.)

If self test does not end well, the red indicator remains on.
In such a case one can suspect malfunctioning of the ABS ECU or
the hydraulic unit.

In my case, three years ago I got the ABS warning light
constantly on. I got ABS ECU replaced ($200 used one) and one of
the rear sensors, too. ($150). A year or so later I had again the
problem with the ABS. Then self test was performed in a peculiar
way: ABS warning light went on, then blinked 3 times and then
went off even before I started the engine. After replacing the
hydraulic unit ($300 used one) self test was done O.K. Then I had
to replace the other rear ABS sensor. 

Anyway, I suggest that you test the operation of your ABS system
when the warning light is off. Go to a dusty road, take 2 persons
with you, place them 20 metres ahead on both sides of the road
and when you come in line with them, put on the brakes to block
the wheels. (If you are alone, check the ruts behind the wheels.
If the car slips 2 metres, the eyewitnesses should report to you
that the wheels blocked several times for an eyewink, turned a
bit and again blocked and so on... The ruts should be interrupted
- - 2 feet blocking, 2 feet turning etc.). 

Proceed according to what you find out.

Hint #1. The braking of the wheels is somehow X-related, i.e. the
rotating speeds of the front left to rear right wheel are
compared and FR to RL wheel. Consequently, it may happen, that
although let's say rear right sensor is dead the front left wheel
will be blocking. (It happened to me.) 

Hint #2. Usually, rear sensors ar MUCH more error prone than front ones.

Hint #3. Use the "Divide and conquer" technique - split the
problem in two parts and analyse them separately (static vs
dynamic) and integrally only at the end. That means, check what
happens when the car stands still and then when moving. 

You will eventually need help from the repairman. In my case,
firstly they lifted the car, rotated the wheels by hand and
checked the electrical output at each sensor. Later, I was
driving the car while the mechanician sat behind and measured
signals from the wheels to ABS ECU. 

Rajko Sabo, Slovenia
'90 164 QV Zender
'81 Renault 18 TL

e-mail: rajko.sabo@domain.elided
Web: http://come.to/rajko.sabo.si

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