Been lurking for a while, but haven't seen this exact problem from anyone else so thought I'd finally create an account and post...
Vehicle is a '94 K1500 Suburban, JB6 brakes.
A couple weeks ago I was towing a 20' trailer w/ a truck strapped to it, and nearly standing on the brakes to maintain speed down a hill. Got home, pulled the front wheels, and found out my inner pad on one side had gone to metal-on-metal without ever making a sound. Fun times, whatever.
I've had 3/4 ton calipers and front brake hoses sitting around the shop for a while, so decided to put those on along with new pads (obviously). Put bar clamps over the banjo fittings while I was working on everything else to keep the fluid in, but they leaked and MC ran dry, and apparently sucked air into my ABS pump (the 4WAL EBC4). More fun times.
Got everything re-assembled, bled everything following normal manual procedure, took it around the block and just about had to wash my pants. No pedal at all... figured I must have sucked air into the ABS unit and couldn't get it back out, so I started reading more. I don't have a tech1 and don't want to spend $500+ on an antiquated scanner when most of my small fleet is either pre-electronics ('70s) or post-OBD2. So I bled the MC, followed the manual bleed procedure for the EBC4 (opened the side bleeder passages, clamped the valves with bar clamps since I don't have the special tool, top bleeder screws, manual bleed till clean fluid was coming out, etc.), and all then bled all 4 wheels. Still a craptastic pedal, though it didn't quite try to kill me driving around the block. Tried slamming what brake I had in my gravel driveway to cycle the ABS, and... nothing. Then I realized I didn't have an ABS light, ever. Not even when first turning on the vehicle.
Pulled the cluster and realized some jackass in the past pulled the lights he didn't like - ABS being one of them. Changed out all the lights while I had it out, put it back in, and read out the ABS codes manually: 12, 41, 42, 45, 46, 51, 52, 65, 67. After looking at the code chart (found it in the Actron CP9001 manual, p.88 here: https://actron.com/sites/default/files/pdf_english_16152.pdf), basically everything is open circuit (all 3 pulse width modulation and isolation valves, pump motor relay, and pump motor circuit). On top of that, it thinks it's out of a 2WD vehicle (code 12 instead of 14), so that tells me previous jackass who pulled the ABS light probably tried putting in a junk yard unit or something first, and it either never worked or failed. Additionally, the "clear codes" jumper sequence from the FSM doesn't seem to work with this unit. So, I decided to check all the voltages, make sure grounds and power circuits were good, etc.
Good news is, all of the voltages in the connectors seem correct. Bad news is, while I was testing, the 2-pin connector sprung back and arced a few times against the ABS module housing. Didn't seem to blow anything up (no fuses, etc. that I could tell, but suddenly the truck will crank but not start. The ECM seems to be OK - I have an OBD1 scanner that will do most things except cycle ABS, and it's reading everything I would expect it to read. But... no spark. I haven't been down the entire rabbit hole of "what could an arc have blown up somewhere else." I did hear some sort of pop or other noise in the engine compartment when it happened (from somewhere else, not from the arc), but I still have voltage on the 2-pin connector and all the other places I would expect in the ABS connector, and no fuses blown. Could back-EMF from the arc have taken out my ICM? That seems like the most likely bit I can think of? Anything else that would be top of mind to check? This truck has been dead reliable for the 6ish years I've had it, apart from the occasional drained battery for no apparent reason.
Semi-related question (with all that background out of the way) - I have a wrecking yard ABS module (from a 4WD) on the way, but in the short term I was hoping to just bypass the unit and make sure everything else is solid in the brake system. I don't want to cut, bend, or re-flare lines as I plan to put a new module in, but I'm having a helluva time finding adapters for the oversize fittings GM used. Brakequip seems to have one for 1/2-20 to 3/8-24 x 3/16 line (for the fronts), but I can't find anyone who stocks it, locally or online. The rears are more of a pain - if my calipers were correct (the measuring kind, not the brake kind), it looks like the line from the prop valve ends in a 3/8-24 or maybe 7/16-20 (couldn't get on it straight), while the line out to the rear axle seems to be a 9/16-18. Finding adapters, short hoses, unions, or some combination to connect those two has been pretty near impossible. Anyone have a working combination of parts (pref. with part numbers) to connect those two lines? If someone makes about a 1' rubber hose with the correct female fittings on the ends that would be perfect for my test needs, but the catalogs have been failing me trying to look that up. The usual suspects (Raybestos, Centric, Sunsong, etc.) seem to just list by application, but can't filter by fitting size.
Vehicle is a '94 K1500 Suburban, JB6 brakes.
A couple weeks ago I was towing a 20' trailer w/ a truck strapped to it, and nearly standing on the brakes to maintain speed down a hill. Got home, pulled the front wheels, and found out my inner pad on one side had gone to metal-on-metal without ever making a sound. Fun times, whatever.
I've had 3/4 ton calipers and front brake hoses sitting around the shop for a while, so decided to put those on along with new pads (obviously). Put bar clamps over the banjo fittings while I was working on everything else to keep the fluid in, but they leaked and MC ran dry, and apparently sucked air into my ABS pump (the 4WAL EBC4). More fun times.
Got everything re-assembled, bled everything following normal manual procedure, took it around the block and just about had to wash my pants. No pedal at all... figured I must have sucked air into the ABS unit and couldn't get it back out, so I started reading more. I don't have a tech1 and don't want to spend $500+ on an antiquated scanner when most of my small fleet is either pre-electronics ('70s) or post-OBD2. So I bled the MC, followed the manual bleed procedure for the EBC4 (opened the side bleeder passages, clamped the valves with bar clamps since I don't have the special tool, top bleeder screws, manual bleed till clean fluid was coming out, etc.), and all then bled all 4 wheels. Still a craptastic pedal, though it didn't quite try to kill me driving around the block. Tried slamming what brake I had in my gravel driveway to cycle the ABS, and... nothing. Then I realized I didn't have an ABS light, ever. Not even when first turning on the vehicle.
Pulled the cluster and realized some jackass in the past pulled the lights he didn't like - ABS being one of them. Changed out all the lights while I had it out, put it back in, and read out the ABS codes manually: 12, 41, 42, 45, 46, 51, 52, 65, 67. After looking at the code chart (found it in the Actron CP9001 manual, p.88 here: https://actron.com/sites/default/files/pdf_english_16152.pdf), basically everything is open circuit (all 3 pulse width modulation and isolation valves, pump motor relay, and pump motor circuit). On top of that, it thinks it's out of a 2WD vehicle (code 12 instead of 14), so that tells me previous jackass who pulled the ABS light probably tried putting in a junk yard unit or something first, and it either never worked or failed. Additionally, the "clear codes" jumper sequence from the FSM doesn't seem to work with this unit. So, I decided to check all the voltages, make sure grounds and power circuits were good, etc.
Good news is, all of the voltages in the connectors seem correct. Bad news is, while I was testing, the 2-pin connector sprung back and arced a few times against the ABS module housing. Didn't seem to blow anything up (no fuses, etc. that I could tell, but suddenly the truck will crank but not start. The ECM seems to be OK - I have an OBD1 scanner that will do most things except cycle ABS, and it's reading everything I would expect it to read. But... no spark. I haven't been down the entire rabbit hole of "what could an arc have blown up somewhere else." I did hear some sort of pop or other noise in the engine compartment when it happened (from somewhere else, not from the arc), but I still have voltage on the 2-pin connector and all the other places I would expect in the ABS connector, and no fuses blown. Could back-EMF from the arc have taken out my ICM? That seems like the most likely bit I can think of? Anything else that would be top of mind to check? This truck has been dead reliable for the 6ish years I've had it, apart from the occasional drained battery for no apparent reason.
Semi-related question (with all that background out of the way) - I have a wrecking yard ABS module (from a 4WD) on the way, but in the short term I was hoping to just bypass the unit and make sure everything else is solid in the brake system. I don't want to cut, bend, or re-flare lines as I plan to put a new module in, but I'm having a helluva time finding adapters for the oversize fittings GM used. Brakequip seems to have one for 1/2-20 to 3/8-24 x 3/16 line (for the fronts), but I can't find anyone who stocks it, locally or online. The rears are more of a pain - if my calipers were correct (the measuring kind, not the brake kind), it looks like the line from the prop valve ends in a 3/8-24 or maybe 7/16-20 (couldn't get on it straight), while the line out to the rear axle seems to be a 9/16-18. Finding adapters, short hoses, unions, or some combination to connect those two has been pretty near impossible. Anyone have a working combination of parts (pref. with part numbers) to connect those two lines? If someone makes about a 1' rubber hose with the correct female fittings on the ends that would be perfect for my test needs, but the catalogs have been failing me trying to look that up. The usual suspects (Raybestos, Centric, Sunsong, etc.) seem to just list by application, but can't filter by fitting size.
