ABS Light
Thread Starter
Rennlist Member
Joined: May 2007
Posts: 1,702
Likes: 1
From: Society Hill, SC
ABS Light
My ABS light is coming on my C2 after the car reaches the 4mph point. I did the usual of replaceing the relay and fuse. I have a reset switch, but as soon as I reset, the light comes right back on. It doesn't come on when I start the car or reverse it, only going forward. I'm hoping it's just a dirty sensor. Does anyone have any good pics or speecifics on how/what to check clean? I'll be working on it at 1st light tomorrow, so any help would be appreciated.
Drifting
Joined: Jul 2005
Posts: 3,363
Likes: 25
From: NY, USA
Here's what I've gleaned about ABS and PDAS lights/problems from various sources; mostly Rennlist.
Code:
ABS/PDAS
Clock Cold Solder Joints - re-solder both sides of the board
Front boot crash sensor connectors
Clean Accelerometers
Clean wheel sensors
ABS Relays - both?
Alternator - if going bad may provide low charge and cause lights
Check battery voltage - low voltage causes strange problems
Check PDAS control unit connection
unit is mounted wrong-side up so moisture sits in connector and rots it
Check pressure switch seal (C4)
Fuse 15, Relay 51 - maybe just replace these
Ground wire behind pressure switch plug (C4)
Adjust brake fluid reservoir level - few ounces +- can make a difference
Bleed longitudinal and transverse locks (C4)
Check ABS power connection at battery
- it's a piggy back and the nut comes loose
- connect gets corroded and shows intermittently
Main ECU connection pin 26 dirty
Loose wheel nut caused toothed gear to move giving false signals
Check grounds in front trunk
Check Adrian's book
Advanced
Joined: Dec 2007
Posts: 77
Likes: 0
From: S.W. France.
pat056.
Had a similar problem with mine,went through all the items on the list posted by dfinnegan,with no positive results.Then whilst checking the resistance between the terminals on the main ECU,(again nothing positive).Then when I plugged the ECU back in ,hey presto,the lights went off.I figured that I must have been getting a bad contact on the ECU,on inspection all looked OK.But with pokeing around in the terminals with the tester,it squeezed the terminals tighter.
Its worth a try,and costs nothing.
Best of luck!Let us know how you get on.
Marc.
Had a similar problem with mine,went through all the items on the list posted by dfinnegan,with no positive results.Then whilst checking the resistance between the terminals on the main ECU,(again nothing positive).Then when I plugged the ECU back in ,hey presto,the lights went off.I figured that I must have been getting a bad contact on the ECU,on inspection all looked OK.But with pokeing around in the terminals with the tester,it squeezed the terminals tighter.
Its worth a try,and costs nothing.
Best of luck!Let us know how you get on.
Marc.
Drifting
Joined: Aug 2002
Posts: 2,217
Likes: 72
From: Stockholm, Sweden
cleaning the connectors is easy. Just pop-open the black plastic cylinders on the hub/damper, pull apart the connector and clean with 5-56 or similar. Also check the brown ground cable on the wheel hubs/carriers.
Nordschleife Master
Joined: Feb 2007
Posts: 5,095
Likes: 4
From: Cheshire, UK
You can pull the speed sensors out of the hub after undoing a single hexbolt. Clean away all the gunge and filings with electrical contact cleaner and vacuum out the holes before replacing.
However, I cleaned all four because my ABS clearly wasn't working (wheels locked) yet I didn't get a warning light on the dash.
However, I cleaned all four because my ABS clearly wasn't working (wheels locked) yet I didn't get a warning light on the dash.
Nordschleife Master
Joined: Dec 2006
Posts: 5,405
Likes: 75
From: S.E. VA
Trending Topics
Nordschleife Master
Joined: Feb 2007
Posts: 5,095
Likes: 4
From: Cheshire, UK
Yes cleaning the sensors worked wonders for restoring the ABS function to the car.
What I was trying to point out to the OP was that, strangely, I had no warning light to tell me there was a problem (it was the skidding that did that
). Therefore, cleaning the sensors might not help him - my guess would be a break in the circuit somewhere - I heard of story where the cause was a break in the loom between a sensor and the ABS unit.
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Thread Starter
Rennlist Member
Joined: May 2007
Posts: 1,702
Likes: 1
From: Society Hill, SC
Not such good news for me 
I was suspicious my problem could be the battery as mine was completely dead. So I got a new battery. Then:
I topped off my brake fluid to max,\
Just cleaned all the sensors (not a bad job BTW) and cleaned all the connections. Not very dirty.
Checked my wiring and found/repaired an exposed place
Started the car, backed it up, and as soon as I stat moving forward, the ABS light comes on.
Oh well, I now know several ways not to fix my ABS
I'm not sure how I would check the electricals since it only comes on when I'm moving forward.
I was suspicious my problem could be the battery as mine was completely dead. So I got a new battery. Then:
I topped off my brake fluid to max,\
Just cleaned all the sensors (not a bad job BTW) and cleaned all the connections. Not very dirty.
Checked my wiring and found/repaired an exposed place
Started the car, backed it up, and as soon as I stat moving forward, the ABS light comes on.
Oh well, I now know several ways not to fix my ABS
I'm not sure how I would check the electricals since it only comes on when I'm moving forward.
Drifting
Joined: Jul 2005
Posts: 3,363
Likes: 25
From: NY, USA
It seems interesting that rolling forward (only) at 4mph turns off the spoiler warning light.
Could it be clock related? Cold solder joints? Try cleaning the connector for the spoiler control unit?
Coincidences are suspicious.
Could it be clock related? Cold solder joints? Try cleaning the connector for the spoiler control unit?
Coincidences are suspicious.
Thread Starter
Rennlist Member
Joined: May 2007
Posts: 1,702
Likes: 1
From: Society Hill, SC
My clock and spoiler control unit have been disabled since I had the car. My guess is they were disconnected by Synergy (then G&W) when they built the car.
I will look at it though. I've changed the ABS relay and the fuse. I was thinking my problem may be that when the car was moving fast enough for the ECU to recognize the sensors, maybe it's not getting an input? How do you tell if a sensor's bad?
I'm no electrician, but since I'm not working now, a penny saved is a penny earned so I'll keep looking.
I will look at it though. I've changed the ABS relay and the fuse. I was thinking my problem may be that when the car was moving fast enough for the ECU to recognize the sensors, maybe it's not getting an input? How do you tell if a sensor's bad?
I'm no electrician, but since I'm not working now, a penny saved is a penny earned so I'll keep looking.
Instructor
Joined: Jun 2007
Posts: 104
Likes: 0
From: Isle of Skye. Scotland.
Rennlist Member
Joined: Nov 2004
Posts: 309
Likes: 0
From: Vienna, VA
I recently had a similar problem and cleaned the contacts. I then reset the fault using the Hammer. At least in my case, I don't think cleaning the contacts alone would actually get the light to go off.
-Bruce
-Bruce
Drifting
Joined: Aug 2002
Posts: 2,217
Likes: 72
From: Stockholm, Sweden
"It seems interesting that rolling forward (only) at 4mph turns off the spoiler warning light"
I had the same problem last year. It ended up with a really stupid mistake. I had cleaned all the electrical connectors for the ABS during the winter (the black plastic cylinders). And on the left rear wheel I'd mannaged to put the connector in the wrong hole. It's really easy to do when you have three holes in one of the connectors and two on the other. So you have more than one choice when you put them together. So the connector was only "50%" connected. Check this one if your not 100% sure.
I had the same problem last year. It ended up with a really stupid mistake. I had cleaned all the electrical connectors for the ABS during the winter (the black plastic cylinders). And on the left rear wheel I'd mannaged to put the connector in the wrong hole. It's really easy to do when you have three holes in one of the connectors and two on the other. So you have more than one choice when you put them together. So the connector was only "50%" connected. Check this one if your not 100% sure.
Burning Brakes
Joined: Feb 2003
Posts: 985
Likes: 1
"How do you tell if a sensor's bad?" There are a few ways to test the sensor in order of sophistication: 1 - ohmmeter to measure the resistance between the terminals. 2 - measure the AC voltage with an AC voltmeter tapped into the connector and measure while the wheel is moving. 3 - replace the AC voltmeter with an oscilloscope . One should be able to diagnose a bad sensor using 1, comparing resistance values to the other sensors. The sensor should be a contiguous multi-loop of wire around an iron core (i.e. that small rectangle protrousion pictured above) so any out of the ordinary resistance (i.e. when compared to the other sensors) values would be suspect.
Hope this helps
Bill
90C2
Hope this helps
Bill
90C2