ABS Woes Continue- Still Stumped
#1
Racer
Thread Starter
ABS Woes Continue- Still Stumped
Hi All-
I have a 93 C2 and an ABS that doesn't work. The warning light works but doesn't illuminate to indicate a problem with the ABS. I know it doesn't work because I can lock up the front wheels (not sure why the back ones don't lock up).
Here's what I've done to try to eliminate the problem:
I assume that because I the warning light is not illuminating that ball the sensors and related wiring is OK (I also inspected them as mentioned above).
Based on the info above I'm suspicious it is an electrical issue. It seems like the motor is not being told when to turn on. Any ideas on items to check are welcome.
Breaking the pump open was pretty fun and informative but required 2L of fluid afterward to bleed all the air out. Here are a few pictures of the process- note the waxy build up on one of the pistons- I thought that was the source of my issue but the system still didn't work upon reassembly. I melted the wax away by putting the piston in a bath of denatured alcohol.
Look Mom No ABS
ABS motor, left, and pump, right, with pistons exposed.
Strange wax found on one piston.
Clean piston parts
I have a 93 C2 and an ABS that doesn't work. The warning light works but doesn't illuminate to indicate a problem with the ABS. I know it doesn't work because I can lock up the front wheels (not sure why the back ones don't lock up).
Here's what I've done to try to eliminate the problem:
- Changed brake fluid.
Cleaned all ABS electrical contracts to the battery and ground,
Cleaned the wheel sensors (which were already pristine), the associated plugs and inspected all the sensor wires for damage,
Inspected fuse #16 and relay #34 on the main panel as well as the 2 relays on the ABS itself for damage,
Pulled the #34 relay while the car was running and the alarm sounded in the car and was immediately silenced once returned,
The ABS warning light illuminates with the other warning lights upon start-up but not otherwise,
Removed the ABS pump (see pics below) and cleaned the pistons,
Inspected and cleaned the pins on the large plug on the ECU (also applied a little dielectric grease on them to prevent any corrosion in the future),
Jumped the abs motor (connected the #9 pin on the pump directly to the battery) and the motor runs,
Jumped the fuse box relay R34 between terminals 30 and 87 and can hear one of the relays on the ABS click but the motor does not turn on, should it?
I assume that because I the warning light is not illuminating that ball the sensors and related wiring is OK (I also inspected them as mentioned above).
Based on the info above I'm suspicious it is an electrical issue. It seems like the motor is not being told when to turn on. Any ideas on items to check are welcome.
Breaking the pump open was pretty fun and informative but required 2L of fluid afterward to bleed all the air out. Here are a few pictures of the process- note the waxy build up on one of the pistons- I thought that was the source of my issue but the system still didn't work upon reassembly. I melted the wax away by putting the piston in a bath of denatured alcohol.
Look Mom No ABS
ABS motor, left, and pump, right, with pistons exposed.
Strange wax found on one piston.
Clean piston parts
Last edited by YaHoo!; 03-08-2015 at 11:41 AM.
#2
I wonder if that is the whitish wax that was a culprit for blocking lines in 993's.
https://rennlist.com/forums/993-foru...-abs-pump.html
https://rennlist.com/forums/993-foru...-abs-pump.html
#3
Three Wheelin'
I had similar symptoms to this and the issue was in the ABS unit, the dedicated bosch ABS test tool was used to discover the ABS unit was building pressure, holding pressure but not then releasing. I think the part of the ABS pump you rebuilt (kudos) are different to the components that caused my issue.
#4
See if you can find another lister fairly nearby with an abs controller you can borrow to see if it is the culprit. If it is, you might source one from a parts yard, or send it to a DME rebuilder to see if it has failed internal cold solder joints.
#5
Racer
Thread Starter
I had similar symptoms to this and the issue was in the ABS unit, the dedicated bosch ABS test tool was used to discover the ABS unit was building pressure, holding pressure but not then releasing. I think the part of the ABS pump you rebuilt (kudos) are different to the components that caused my issue.
I'm still convinced it is something related to powering the the motor on the pump- it is not knowing when to turn it on. Another key piece of info may be that it does not do the system test at ~6mph. Just rechecked the ECU plug again last night and it looks brand new, no issues.
Any other suggestions? Thanks everyone.
#7
Racer
Thread Starter
Hm, can't imagine what they replaced. I looked at my motor/pump last night and the only other thing I can see on it are the three solenoids which don't look like they can be removed or replaced.
Trending Topics
#8
Three Wheelin'
They replaced the whole unit, but it was those solenoids that weren't doing their job as I understood it at the time. They had the car for a month trying to figure it out!
#9
Racer
Thread Starter
Alex did your unit run the self test?
#10
Three Wheelin'
If brake fluid passes through the solenoids, which I think it does, then before dropping the big bucks on a new pump I could run denatured alcohol through the system as described above in an attempt to clean any wax in the solenoids and perhaps have them function properly.
Alex did your unit run the self test?
Alex did your unit run the self test?
Not sure what you mean by self test, the warning light behaved normally ie it came on with ignition and then went out. They used the bosch tester which allowed them to trigger each stage of operation: build, hold, release, pulse - at which point they located the issue.
#11
Racer
Thread Starter
Thanks, this info is helpful. Interesting and maybe related- when I had all the brake lines off the pump I blew through the orifices (blowing into the pump) to ensure there was clear passage- they all were clear but some passages allowed easier or more air flow than others. I wonder if the flow resistance in all of them should have been the same.
Our cars run an ABS system test at around 6MPH to make sure the system is operating.
So my next question to the Rennlist experts is if I'm getting a high pressure reading due to the "clogged arteries or solenoids" would that somehow prevent the absent self test at 6 mph? In that test for a C2 I assume the pump runs and one can hear it- is that a correct assumption?
Thanks all.
So my next question to the Rennlist experts is if I'm getting a high pressure reading due to the "clogged arteries or solenoids" would that somehow prevent the absent self test at 6 mph? In that test for a C2 I assume the pump runs and one can hear it- is that a correct assumption?
Thanks all.
Last edited by YaHoo!; 03-09-2015 at 11:07 AM.
#12
Racer
Thread Starter
Thanks, this info is helpful. Interesting and maybe related- when I had all the brake lines off the pump I blew through the orifices (blowing into the pump) to ensure there was clear passage- they all were clear but some passages allowed easier or more air flow than others. I wonder if the flow resistance in all of them should have been the same.
Our cars run an ABS system test at around 6MPH to make sure the system is operating.
So my next question to the Rennlist experts is if I'm getting a high pressure reading due to the "clogged arteries or solenoids" would that somehow prevent the absent self test at 6 mph? In that test for a C2 I assume the pump runs and one can hear it- is that a correct assumption?
Thanks all.
Our cars run an ABS system test at around 6MPH to make sure the system is operating.
So my next question to the Rennlist experts is if I'm getting a high pressure reading due to the "clogged arteries or solenoids" would that somehow prevent the absent self test at 6 mph? In that test for a C2 I assume the pump runs and one can hear it- is that a correct assumption?
Thanks all.
#13
Burning Brakes
The self test is just the electronic side, power ok, ecu ok, wheel sensors ok. The pump and internal solenoids are not operated during the test, there is no feedback from these items to the ecu anyway that I'm aware of which is why the Bosch tester is so useful.
#14
Nordschleife Master
The same happened to rennlister 'TDIquattro'. He fixed his problem by transferring parts from a mercedes ABS pump which is almost identical to the 964 one.