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Update: I measured the ABS sensor resistance values at the ABS Module connector and found that my right rear sensor "signal" is not reaching the module due to some harness issue (connector, etc.). The sensor itself measured out at 1kOhm, so I will look at the wiring and find the fault. Once this is corrected, perhaps my AWD warning light(s) will go away. I will update soon.
Good for you, you'll find it.
Mine is a C2, but...I had a ABS glitch and had tried ALL of the classic stuff to remedy it; never did find it and pulled the ABS relay as it was getting in my way on the track anyway.
When the car went to Rothsport for a full on race build much of the wiring was removed during the strip. Upon rebuild, the ABS glitch was resolved. We never found out where it was, but it was definitely in the loom (most probably a terminal or mechanical connection) somewhere. (FWIW, I keep the ABS off, but it does function when the cutout **** is un-selected)
This thread couldnt be more timely. I picked my car up after a respray a few weeks back and all was fine at first.
The battery wouldn't hold charge having sat for so long so I bought a new one.
About 3 days later I hit a pot hole (read small crater) and before the suspension had recovered the ABS and diff lights came on.
I had limited success in over filling the fluid but it drains through the over flow and then comes back on.
Ive always had to rev over the 3000rpm to get them to turn out but now they come straight back on and I dont think the central warning light goes out unless I press the switch in the center console.
My brake pedal isnt hard and the car drives fine.
I cant help but feel that hitting pot hole has loosened a connection somewhere? But that doesnt explain the overfill solution.
All I have looked at so far is the level swith on the tank with a ohm meter.
This weekend I will clean up all the battery terminals, earths, ecu connectors and look at the hydraulic switch.
Ill let you know how I get on, but if there are any suggestions they'd be gratefully received
Excellent input from you guys - here's some more data points:
I installed the new ignition coils - engine runs better but no change in the AWD and ABS lights' behavior (wires and caps and rotors already changed, plugs are fine). Some persistent hesitation in the mid range, I'm suspecting my Hall Effect Sensor (since I have a code 34 on my MIL for that). Another topic for another thread...
Taking jlMartin94's idea about the voltage dipping below 9VDC during cranking and upsetting the system, I came up with a test that did not require an analog volt meter: While driving in 2nd gear at 45 mph, I turned the ignition switch off, counted to ten, and let the clutch out to roll-start the car in second (Nanny-state note: never do this because your steering wheel will lock up). This gave me an engine start with no current drain. The result? No lights came on, including the Central Warning light. I drove in darkened dash delight for ten minutes, thanking our French friend for his tip. Then I hit a rough patch of road and the Central Warning/AWD/ABS lights came back on, much to my dismay.
So, maybe I have a combination of a weak battery plus a right rear ABS sensor harness loose connection. My battery reads 12.05 at rest, which is a hair low, but my alternator appears to be strong at 14.1 volts output at the battery at idle.
I will track down the right rear ABS sensor wiring problem until I see continuity to the ABS module and report back. I believe that I have the problem surrounded, but not fully discovered as of yet.
I still consistently get the Central Warning light on at every start up - I will try cranking the engine with a battery charger engaged to see if that keeps the voltage sufficiently high. I have been waiting for my hydraulic pump to fully pressurize before cranking the engine (per jlmartin94's tip) and this does not make a difference - yet. We'll see how it behaves once the ABS harness is fixed.
So, I changed the battery to a Bosch S3 rather than the cheap Lion branded one. They are the same spec but had no problems with the S3 before.
I cleaned up the earths, plugs and relays on the hydraulic unit.
Lastly I pulled the big plug off the ABS module and found two of the contacts where completly white. I cleaned them up and gave all the others a quick rub over.
All tyres to 36 psi, they were all about 34 so dont think it was that.
The result... drove 5 miles (update 15 miles now over three trips) and NO ABS / Diff lock lights or alarm
The central warning light still came on but no other warnings (the remote locking seems to have stopped working now)
Last edited by NateSaJack; 09-19-2014 at 04:46 PM.
My battery reads 12.05 at rest, which is a hair low, but my alternator appears to be strong at 14.1 volts output at the battery at idle.
12,05 v ... which is insufficient for a cold start ... mainly on a C4 just after the pressurise step which last almost 60sec ...
you should have at least 12,7 volts... for a good shaped battery
Originally Posted by flamefront
I will track down the right rear ABS sensor wiring problem until I see continuity to the ABS module and report back. I believe that I have the problem surrounded, but not fully discovered as of yet.
I still consistently get the Central Warning light on at every start up - I will try cranking the engine with a battery charger engaged to see if that keeps the voltage sufficiently high. I have been waiting for my hydraulic pump to fully pressurize before cranking the engine (per jlmartin94's tip) and this does not make a difference - yet. We'll see how it behaves once the ABS harness is fixed.
what i had noticed : even if you wait for your hydraulic pump to stop , you can notice that the battery suffer this 60sec duty cycle.
the voltage level get very low ( 11v ? ) and THEN the battery begin a auto-recharge cycle ( yes the lead battery are known to self recharge... )
So you "have to wait" some time ( more or less ) before the battery can deliver 12,7 volt for the starter motor .
I have heard some friend of mine , who tell me some people tell them to wait that the airbag light goes out before cranking .. they doesn't know why ..
i suppose that with the time ( those car are 20year old .. ) the battery are less powerfull and the empirical methode is to let the battery self recharge between each duty cycle ..
That said, you may have also a problem of bad contact betwen the harness and the ABS sensor ......
Update: I crawled up under the beast and started tracing the RR ABS sensor harness and found this oddity that is not on the OE schematic:
Being new to the Carrera 4s, I have not seen one of these: The ABS sensor signal passes into this connector and two leads (with two wires each) come out of it. This is ~200 mm upstream of the connector that the regular ABS sensor harness plugs into. Of the two connectors leading into the car's harness, one appears to go to the ABS module (and this is the one I don't have continuity through) and the other shows 377 Ohms across the two pins. Inside the white "barrel" connector, one pair of pins correctly show the expected 1032 Ohms of the connected & functional ABS sensor, and the other pair of pins show 362 Ohms but I cannot discern to what they are connected.
Anyone have any clues on this? As I said, the factory schematic shows nothing of this arrangement...
Okay, I guess that second set of wires is for the RR brake pad wear indicator. This is shown in another schematic but it is not clear that it is in the same connector. I did not discern that from my vantage point from underneath the car - Please excuse my learning curve.
I would still like to know if anyone knows where the "T2" connector shown on the schematic is located where the ABS and Inertia Sensors connect into the harness...
I found the ABS "T2" connector right in the area jlmartin said it would be - along the inner RH fender back near the firewall. Pulled the connector open and confirmed the wiring colors with the OE schematic. Then I proceeded to isolate the discontinuity between the female end of this T2 connector and the RR ABS sensor connector near the RR rear trailing arm. Now to fish through the interior to find the harness and the offending break.
This T2 connector also carries the wires for the lateral and longitudinal accelerometers, so this little bugger can cause all sorts of trouble for us C4 owners who are chasing down flashing dash lights.
Having thought I had solved mine it has come back sporadically. A thread on 911UK caught my eye so I have dealt with the 'cold joints' on the clock too. It works and the ABS/Diff light doesn't require a blip any more to clear. I also get a battery light and belt warning (both go out on startup).
I am going to attack the ABS harness discontinuity in the firewall-to-rear bulkhead section this weekend - it will be a nasty endeavor, I'm afraid.
I have been in denial about the clock solder joints up to now, but your tip brings it to mind again. If I still have the warning lights once I get continuity to the ABS module re-established for the RR ABS sensor, I will go and do that fix. Thanks for the reminder.
I had started this hunt at the ABS sensors themselves and found them to be okay, then I went off to other rabbit-trails of diagnostics suggested in this excellent forum. For those of you reading this thread at the start of your own hunt, I would advise going directly to the ABS Module connector and reading each ABS sensor's pin resistances as shown above "first-thing". It actually is a much easier job to check for 1k Ohm at each pin at the module connector than it is to pull each wheel and measure each sensor at its connector. If you have a problem at the connector with a particular corner's ABS sensor, you can go to that one to investigate. Of course, just having 1k Ohm resistance is not sufficient proof that a sensor is working - many folks have fixed their problem by cleaning the iron debris off of their ABS sensors' faces/heads. But, the resistance is a 15 minute check that gets you started.
I had avoided the ABS module for a long time due to "all those pins", but that was just my old analog self being lazy. The factory wiring diagram clearly shows the pin call-out and it is easy work with a DVM. It's also a good time to clean up the pins on the module's input side, which often get corroded.
Luckily, these cars can be driven (for years, it seems) with these flashy light things going off without consequence...so we can use the cars in the meantime.
Mines come back with a vengeance!. No lights on at start-up but the Diff then ABS light will come on within a couple of minutes of driving.
Now that I have dealt with the cold solder fault at the clock it is very obvious that the diff light comes on, followed by the alarm and then ABS light, does this suggest anything to anybody? No particular speed but wheels are rolling.
I have tried the hardwire pins 87 to 30 on the R34 and cleaned out the two accelerometers in the tunnel (then very very clean to start with).
I'll try reading the pins as you suggest FlameFront but I fear I may have to track down a hammer or go grovelling to the local OPC
09-19-2014, 10:36 AM
