KenRudd

I have not abandoned this thread, just have not had time to follow up. Hopefully will have updates this week.

GregBBRD

The problem isn't the missing outer insulation.....every one of the looms looks like that.

The problem is almost always a broken wire right at the plastic end connector down by the wheel....inside the actual wire insulation.

Leave the looms in place. Hook up an ohm meter onto each individual ABS from the plastic connector at the wheel to the plastic connector inside the engine compartment. You will have to experiment a tiny bit to figure out which wire is which. Gently start wiggling the loom around...like it would if the car hits a bump or the wheel turns. GENTLY....radical movements never seem to open the circuit.

There's other ABS problems, obviously, but for the problem descibed, these looms are the cause, 95% of the time.

KenRudd

Went through the above recommended tests.
Ran the car, left it running, jacked it up still running and wiggled wires from sensor up to connector where sensor joins main ABS harness on inside of fender on each side. Wiggled gently, wiggled firmly along every axis from sensor to connector on both sides. Could not induce the error.

Visually inspected wiring. As typical, outer rubber was in very bad shape, but could find no obvious breaks or fraying. However, did find it pinched between brake lines on driver side:



Close inspection shows no obvious fraying, chafing or breaking, but I rerouted wiring properly. That was the closest thing I found to a smoking gun.
I re-sheathed the wiring on both sides with a combination of heat shrink and Silicone Rescue Tape to prevent further damage. I also replace the grommets where the wiring passes through the fender to prevent damage there.

The connectors on the inner fender wells were crumbling, brittle messes. They will need to be replaced with something better in the near future ( Packard connectors?) but for now I repaired, De-Oxited and sealed the with Dielectric grease, then heat shrink on the outside to insure physical integrity. The wiggle test ( both Gentle and firmer) shows they maintain connectivity. They will be zip-tied in place once testing is complete, as the plastic clips that hold them are also not trustworthy at this time






I took the time to again thoroughly clean the ABS ground connections, and treat with De-Oxit:




I then went to the main connector at the ABS control brain and again connected my DVM based on this pinout:
* Speed sensor, front, left between term. 4 and 6
* Speed sensor, front, right between term. 21 and 23

and went through the wiggle test, gently and then firmly on all axis all along the wire. Never saw the impedance change by more than a few Ohms (typical below)


So, while I have cleaned all connections, and improved routing, I have not been able to replicate the issue and I have not found a definitive smoking gun.
'

Captain_Slow

Ken - The hunt continues...but you have done a great job. I'm following closely as I have the same ABS issue and want to improve condition of wires and connections while going through the system. Do you feel you can rule out wire breaks and connection issues at this point?

KenRudd

Nope, the wires from the sensor to the connector are s**t and may still be the issue, so I am only maybe 75% convinced they are now not the issue. I'll replace them with new (if available) at some point in the near future, but I'd really like to confirm root cause before just throwing parts at the problem.

Captain_Slow

You're reading my mind. Since Greg posted about the common breaks hidden inside the insulation or boots of connectors, I've started leaning toward new replacements as well. But I also want to know where the problem is rather than buy new for all four corners (and possibly still have the problem).

928wolf

Bumping this one, I have an ABS problem on my '85 Euro. It sounds like if I need to replace sensors they are no longer available? Did anybody come to any conclusions on the Volvo Sensor?

Thanks,

buccicone

KenRudd

So, two years into this intermittent issue. I have replaced:

• ABS Brain
• ABS Pump and pump mounted relays
• CEP Relay
• CEP Fuse
• Both Front Sensors
• Both Front Sensor Connectors
• Both Rear Sensors
• Both Rear Sensor Connectors

Have cleaned and/or DeOxit'd the

• Main connector to the ABS brain
• Ground Points
• CEP Connectors
• Sensor teeth on the axle/hubs

So,the only thing that has NOT been replaced in the entire system is the actual wiring harness.

System will still fail on a bump. Sometime shortly into a drive, sometimes after 20 minutes. Sometimes big bump, sometimes minor. Weather does not seem to matter. When it fails, it becomes VERY easy to lock front brakes. Failure Mode is also know as Flat Spot Mode on the track.Only way to reset is full power cycle.

I am trying to noodle a way to test wiring harness for intermittent faults, both sensor and power faults. I can connect my O-Scope or Voltmeter, but it will be challenge to drive around, hit bumps and look for what may be very intermittent transient signals. So, I am open to suggestions on testing the harness. Or something else I may have missed.

KenRudd

BTW: I am well aware that:

• It is possible that in my replacement cycle, I actually fixed the original issue and broke something else causing the same symptoms, or;
• I replaced a faulty item with another faulty item.

However, I am hoping Occam's Razor is on my side for once and that those conditions are highly unlikely. Otherwise, down that road lies insanity.

I also know that I would fire a mechanic who just threw parts at a problem until it was fixed, but the intermittent nature and difficulty in reliably reproducing this issue in the garage has left me with little alternative.

SeanR

Have you checked the ground wire that runs from the rear wheels and above the transmission. It's a combined ground. Took me removing the trans on my car to see that it was the reason my ABS was never working correctly.

M. Requin

Oh man, up on the lift she goes!

GregBBRD

When it gets tough to figure out.....

You pull out this:


Drive the car until the light comes on, unplug the brain, and run the test.

fiatrn

My 86 was having the exact same symptom - ABS light after a bump, reset perfectly with restart, everything appeared perfect. Appeared. The wire fault was INSIDE the barrel shaped connector, and would measure ok with a ciruit tester, even with wiggling and jouncing. But I opened the barrel connector and could see one of the black wires frayed. Fixing it was difficult - should have replaced it - but it worked out perfectly and the problem immediately stopped happening.

SeanR

Mine will only work up to '89 cars and not the later ones, connector is different. Do you have two separate connection plugs?