94 ABS Problem

[IAmTodd]

I'm trying to clear up all issues on my truck before winter rolls around. I've had an intermittent ABS for the entire time I've driven the truck. It's on more than it's off though. I've never tested the operation of it when the light is off. Sometimes it's off when I start the truck and after a mile it turns back on, sometimes it's on immediately after starting.

I've tried the jumper wire method on diagnostic port between the BL and LB/BL wires, turn the truck on and wait 5 seconds and pull the jumper. The ABS light stays solid, no codes flash. Would that indicate a controller issue or am I doing the test incorrectly.

I'm getting ready to pull the axles so I'll have easy access to each sensor. Is it possible to test them buy measuring the resistance?

 

[Anime]

What are the symptoms other than the light staying on? Does the ABS still engage/disengage properly or it's erratic and sometimes doesn't activate when it should?

The pin/jumper method of reading codes isn't very reliable, you have to count flashes and assume you count correctly and could be chasing a wrong code. Easier to get a Innova 3145 code reader and plug it in, saves a lot of time and headache and points you to the problem if it's somethiing the computer can pinpoint.

Sometimes it's just the sensors themselves. You don't need to pull axles or anything, the front ones pop right out of the knuckles and the rear one is on top of the differential. It could even be you just have a short, the wires going to these things tend to degrade and often you'll find the plastic sheath has cracked and gone and the wires are exposed and sometimes in bad shape. The ABS exciter rings on the rotors can get dirty and caked with mud or debris, and the sensor can get covered with grease and brake dust. Sometimes just taking apart the thing when doing a wheel bearing/ball joint job and cleaning it all up makes all the difference. Sometimes you'll just need to replace the sensors.

If it's something more severe, it could be the ABS Hydraulic unit ($$$) or the controller itself,but hopefully not since they are very, very expensive. Usually it's just the common stuff with sensors/wires though.

You might also want to check/replace the ABS relay, it could just be an old/sticky relay problem.

 

[IAmTodd]

I don't believe the ABS is working. The one time I was able to lock up the front passenger wheel. That has been a few weeks ago. I've never felt the system pulse. One issue could be I'm still running the auto ECU with a manual trans. The cruise control is also non-functioning.

I swapped the relays around with the fuel pump to ensure that wasn't the issue. The front rotors are new, when I did those I forgot to clean the one sensor off but I did on the opposite side. The face of them was dirty and could be the issue. I have been searching quite a bit and it seems worn wiring is somewhat common and something I didn't think about, good call there. I'll also look into getting that scanner. Will be helpful if I keep this thing around I imagine.

I'm tearing into the axles this weekend so I'll be able to clean off the sensors again. I read somewhere of putting a voltmeter on the pigtail and spinning to wheel to see how much voltage the sensors create and compare. If it turns out to be the hydraulic unit or the controller and I can't find a salvage yard item it looks like I'll be learning to drive without ABS. Although there are times (normally when the light is off) that I can hear something up front when I turn the key.

 

[IAmTodd]

I've taken the truck apart before I was able to scan for codes. I've come across another slight issue. When remove the drivers side spindle I didn't realize the block around the speed sensor had to be removed first and resulted in the destruction of the block (guard?).

I also managed to destroy the sensor. Seeing that they're $30 a piece I'm temped to just pull the fuse and relay and remove the bulb but I would like to have it working again. Is that aluminum block necessary for operation? I removed the drivers side by drilling out the stupid 12 point bolt. I ordered the correct socket except it rounds the head off each bolt I find at the junk yard.

 

[Anime]

Which block are you referring to? The sensor is one whole assembly that should pull out from the spindle after you remove the nut. If the metal cover that faces the rotor came off, the sensor was old and falling apart.

$30 for a new sensor is a DEAL for a quality one. Generally it's just the Dorman brand ones that are that cheap. If you can get a better brand for $30 each, get two and you've made out good.

Generally for the 12pt ones it helps to have a quality 12pt 6mm socket, the cheapos aren't very good as you've found out. Snap-on, MAC, Matco, SK and a few others made them, they cost a few dollars just for that one tiny socket but it's worth it.

I don't know if anyone has replaced the bolt with another size, but I'm about to pull mine shortly and will be looking for a replacement, hopefully something with the same thread and length is available with a 6pt 7-8mm head.

 

[IAmTodd]

No, I'm talking about the block that goes around the sensor, it's the one the 6mm bolt holds in. I'm not really willing to dumb a whole load of money into this ABS system considering I don't know what else is wrong with it.