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Discussion Starter #1 (Edited)
Hi all, I often read your forums from my google searches but it is now time for me to write down something.
I have a Laguna II F9Q 758 96kw.
One otherwise happy morning I got the "STOP" light, together with the fixed handbrake and ABS light on the dashboard. The ABS actually doesn't work and the speedometer doesn't move anymore (fixed on 0). The odometer is stuck on the same value. This happened right after turning on the engine, while the previous drive was all right without any alarms.
The diagnosis report the following DCT errors:
P0500 - Vehicle Speed Sensor VSS Malfunction
P0571 - Cruise control/brake switch A - circuit malfunction
P0575 - Cruise control system - input circuit malfunction

Clearing the errors does not turn off the warning lights, also if re-reading DCTs shows nothing. The DCTs reappear the next time I turn the engine on.

Connecting the ECU(ECM) diagnostic I see that the speed sensor somehow always reads 25km/h, and one of the 2 brake switch values does not change.
As suggested by my mechanic, I tried to remove the brake switch and tested it manually. (BTW its location is NOT on the passenger side as I read somewhere, is right over the brake pedal. Still very ticky position to operate 馃槫)
The switch seems to work correctly as both the normally open and normally close do switch correctly.
On the other hand, I read the voltage on the connector and both sides measure something near 12V, indicating that the electric continuity is ok.
Also tried manually short-circuiting them, while reading the ECU, one is read, the other is not 馃槶.

Now the questions and doubts that still afflict me:
Is it possible that the VSS and the brake switch broke at the same time? Or is it more plausible that one of them made the ABS angry and it doesn't feel happy to send the correct information to the ECM?

BTW I tried to find as much info as possible, and it seems that the ABS reads the wheel speed from 4 sensors, and sends one single signal to the ECM. That makes it difficult to find the point of failure: even if a single speed sensor is very cheap, I can't be sure if or which one I should replace.

And if the brake switch electric signals tested as explained above seem to be correct, why the ECM can't read both signals? (I'm quite sure from a schematic I have, that the brake switch cables are directly connected to the ECM).

Do you have any suggestions or expirience with a similar problem?

Thank you very much!
 

Super Moderator Technical Supremo Platinum Member
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Have you looked at the speed sensors on the wheels?
Not unknown for one to fall off or for a wire or connection to fail.
Fairly certain the brake error is cos the system is reading a wheel turning when parking brake is on.

Disconecting each of the sensors in turn should lose the 25Km/h reading and identify which is the culprit... fairly certain only one provides the speed but not sure which one.
 

Super fantastic Mod Technical Supremo Nice Guy
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You should get a reading off all 4 wheels if abs sensors are fitted to them.
Ignore the brake switch it's a Red herring,
Cruise control gets disabled if a fault is logged .
Once VSS is sorted you will get CC back
Take the car for a run, assuming Diagnostics reads wheel sensors. 3 will show the same one speed.. Faulty one will show another speed or not move ..
 

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Discussion Starter #4
Have you looked at the speed sensors on the wheels?
Not unknown for one to fall off or for a wire or connection to fail.
Fairly certain the brake error is cos the system is reading a wheel turning when parking brake is on.

Disconecting each of the sensors in turn should lose the 25Km/h reading and identify which is the culprit... fairly certain only one provides the speed but not sure which one.
Thank you, I actually did not look yet at speed sensors because AFAIK they are below the car (near the wheels?) and I have no safe means to lift it, but I can try to clear the errors while the parking brake is deactivated and then start the engine again :unsure:.

You should get a reading off all 4 wheels if abs sensors are fitted to them.
Ignore the brake switch it's a Red herring,
Cruise control gets disabled if a fault is logged .
Once VSS is sorted you will get CC back
Take the car for a run, assuming Diagnostics reads wheel sensors. 3 will show the same one speed.. Faulty one will show another speed or not move ..
I don't know how to read single sensors. I'm using ddt4all with a bluetooth ELM327 adapter, and it does not detect the ABS ECU, maybe because that ECU only works on CAN bus and not on KWP?
Anyway on the ECM ECU, I can only read one vehicle speed value, and this agrees with the ECM schematic I have, witch only shows one VSS signal.

Do you know a good way to read the ABS ECU?
 

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Discussion Starter #5
Hello,
I made other diagnostic tests and I'm starting to think that the ABS ECU is completely gone (or not powered).
That's why:
1. From the handbrake ECU, I was able to read front and rear wheels speed, and it read like this:
181089

Also, from the ECU DTCs, I get this error:
"DF037 (DTC5181A1) ABS MULTIPLEXED EMISSION MISSING"

2. I tried to clear the errors from the ECM ECU and unplug the ABS fuse from the fuse box, then started the engine: I got the exact same errors.

I'm going to try with my multimeter to measure the continuity on the ABS fuse connector and the current inside it. BTW I already tried changing the fuse with a new one, no results.

Now I read that the ABS ECU is in the front bumper, near the left wheel. As the disassembling process seems very difficult, I will not try it myself. I still hope is a connection/electric problem and not the ECU that needs to be replaced 馃槶 .

Will keep you posted.
 

Super fantastic Mod Technical Supremo Nice Guy
Joined
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Just take the front bumper off, easy on these..
Bolts under the bumper holding the sides to the wing, wheel arches out to get at them.
Under tray off , and its off..

Still confused, whats the VSS doing while driving the car, nothing or ?
 

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Discussion Starter #7
I forgot to mention that the ABS ECU is not being detected at all when scanning.
I tested with the multimeter at the fuse connector and the continuity seems ok (~10V), the current is read just when the ignition is on, and measures around 0.006A (seems bit low but still...)

I read from the Handbrake also this:
181094

Which seems to me indicating a failure in the ABS CAN bus?

And from the UCH screens I found:
181095

(With ignition on and engine off)

And:
181096

(With the engine on)

I don't really know how to read these but I think that the optimal reading for ABS would be the same as injection and airbag units. Do you know what "e8" or "80" means here?

Just take the front bumper off, easy on these..
Bolts under the bumper holding the sides to the wing, wheel arches out to get at them.
Under tray off , and its off..
I've seen a video of a man taking off the ABS (here:
) that scared me a bit. I never have done anything at this level and I'm not sure I will.

Still confused, whats the VSS doing while driving the car, nothing or ?
The VSS while driving the car always read that same value.

BTW Do you know where can I find the fuses/relays map of the box inside the hood? Maybe there's some malfunctioning fuse or relay that controls the ABS unit..?
 

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Discussion Starter #8
Hi all.
This problem got sorted out replacing the whole ABS ECU.
I found a new (used) one with same codes on eBay, and had my mechanic to replace it.
Now everything seems to work fine, no errors or warning lights, ABS is working.

Just one question: attaching pyren and reading the ECU settings, the ABS ECU has, of course, a different VIN and is programmed for a "generic" vehicle while the options list shows my specific car.
Should I go the extra mile and reconfigure the VIN and the vehicle type, or since it's already working I should leave everything as is?
What would be the advantages or disadvantages?

Thanks!
 
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