P38A P1592 rough road signal implausible

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kermit_rr

kermit_rr

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As some of you may already know, I've been getting the ABS and TC light intermittently at startup, if I stop/start the engine, it usually stays away for the rest of the day.
Wabco ECU shows no faults, Motronic shows P1592 and no other faults.
Further digging on nanocom and I see the following with ignition on, engine on or off;
Rough road volts: cycling between 0v and 12v
Rough road status: ACTIVE
Rough running: ON
This means the Wabco ECU is indicating the vehicle is driving on a rough road.
If I open up ABS inputs, I see sensor volts and wheel speed indication all looking normal. In a straight line at low speed (before the diag mode cuts off) all sensors show the same speed.
I've checked connections on the Wabco ECU for corrosion, seems fine, despite showing no faults, i'm wondering if it is failing, at this point I can't see why rough road volts would be getting 12v. I'm tempted to take it out and see if I can look at the circuit board and components for damage/corrosion
 
Yours is Wabco D iirc which is the 4w tc, the expensive ecu unlike B,C and the one that seams to give trouble,
if the wheel sensors are reading right it must be the ecu, mind i do seam to remember someone else with problems that turned out to be either wiring or water getting in the ecu from pollen filter leak.
 
i saw that one too, but mine has 'no faults' in nanocom too, doesn't mean it works!
will see if i can get it apart to see if water had got in, need to use it tomorrow and weds so thurs at the earliest
 
Sounds like a dodgy connection somewhere between ECU and sensors. Think Nanocom only takes a reading once a second on a trace so too slow to catch it.

I'd check RAVE and try and find the connectors but if you have water pouring down on the ECU it cannot help.
 
Found some info on the error code that it could be.open/short circuit to positive.

This implies a wiring problem, but the language is clear as mud. does it mean the positive wire is either broken or shorting to earth? Or does it mean either broken or shorting to another 12v source?

Edit: i think short to positive means a wire is getting volts when it shouldn't be, ie dvm between connection and ground shows a positive value
 
Last edited:
kermit_rr said:
Found some info on the error code that it could be.open/short circuit to positive.

This implies a wiring problem, but the language is clear as mud. does it mean the positive wire is either broken or shorting to earth? Or does it mean either broken or shorting to another 12v source?

Edit: i think short to positive means a wire is getting volts when it shouldn't be, ie dvm between connection and ground shows a positive value
Click to expand...

Er, I think we might be in @pwood999 territory. What happens if you hit it with a hammer?!
 
Just taken the abs ecu out, connections are good and the inside looks good as new.
That's the limit of my electrical expertise, wouldn't have a clue how to do any circuit/component/IO tests
 
Most likely the sensors, but Nanocom isn't fast enough the read them. The ECis probably reporting Implausible because the fault is intermittent.

The sensor connectors go directly to the ECU, so there are no intervening joints. If there's no corrosion at either sensor or ECU end, they could still have loose contacts inside.

If your getting "open / short" errors at same time, then definitely suspect connectors somewhere. this can also be cause by bad earths on the ECU itself.

Have a look at this thread especially post-83 by Marty.
 
pwood999 said:
Most likely the sensors, but Nanocom isn't fast enough the read them. The ECis probably reporting Implausible because the fault is intermittent.

The sensor connectors go directly to the ECU, so there are no intervening joints. If there's no corrosion at either sensor or ECU end, they could still have loose contacts inside.

If your getting "open / short" errors at same time, then definitely suspect connectors somewhere. this can also be cause by bad earths on the ECU itself.

Have a look at this thread especially post-83 by Marty.
Click to expand...
Thanks. I've just now cleared all errors and none have returned, though i have not started or moved the car yet, that's next.
Nano is currently showing rough road signal as active even though it's not moved a mm
 
Nanocom Document shows "Rough Road" an ECU Output rather than a fault ? Not sure what uses it though. The plausibility fault is most likely sonsor disagreements outside the acceptable range (i.e. intermittent connection)

upload_2021-5-14_18-13-19.png
 
It's the motronic ecu that sees the right road signal input.
However!!!
I have managed to catch a code from the wabco!!!

06-05 front right sensor electrical failure

That's progress and something tangible to go on!!
 
Check the front hub ball joints & sensor gaps before you buy new sensors. If gap is too large, or ball joints are loose it can cause sensor problems.
 
I've found the upper and lower ball joints are allowing up and down movement i can feel when i lever on the wheel. Hoping this is the problem!!
 
I would have thought that would just let the whole assembly more a bit, but maybe allowing the driveshaft to more a bit ether way ball joints need doing
 
kermit_rr said:
It's the motronic ecu that sees the right road signal input.
However!!!
I have managed to catch a code from the wabco!!!

06-05 front right sensor electrical failure

That's progress and something tangible to go on!!
Click to expand...

Can you put a test lamp on the wire between sensor and ECU as a load to check for internal break?
 
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