I'll take a crack at this.
Simplified as much as possible.
ABS accumulator simply hangs out on the brake lines passively until the ECM/ABS module determines there's a wheel problem from the speed sensors. Then the ABS circuit (ABS accumulator 'box', ECM/ABS module) kick in to pulse the fluid (correct solenoids activated for specific wheel) in the brake lines to prevent wheel lockup and/or regulate the wheel speed.
The ABS accumulate uses solenoids to control the pulse. Hence there's brake fluid in there with the possibility of air bubbles. If the system is cracked open, yup good chance of air in the system. Sometimes you get lucky.
To purge the air need to bleed the ABS accumulator. Activate the solenoids during the flush. Some ABS accumulators have a specific bleed screw. The unit your swapping pretty sure doesn't.
Bi-directional scan tool. Enables two way communication with the on board systems. Some are better than others. Some mimic bi-directional. All scan tools want to be bi-directional or wish they could be.
Most non factory scan tools operate with some percentage drop from 100% of a factory unit.
Sorry but didn't mean to 'bait' you. ABS seems to particularly hard for scan tools to connect and be bi-directional. Doubt there's a good cheap ABS bi-directional tool out there. Maybe, would love to find a good cheap one and toss in the truck tool bag. Still looking.
Don't worry about brake line configuration. There's a specific pattern to bleed for your truck. Do that.
For the ABS accumulator to be purged need to open the solenoids during the flush process, one at a time, four total. Seems to require your basic standard flush first and then do a second flush to go after the ABS accumulator.
Techstream (Toyota factory software?) runs you through a basic flush first the goes after flushing the ABS on a second pass. Also of note it activates the ABS solenoids for 4 seconds with a 20 second cool down. So in those 4 seconds need to be pushing fluid through to flush out the specific solenoid.
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So here's a "basic" outline of the process. (super simple)
1. Swap in the MC.
2. Do standard flush/bleed all four wheels sequence vehicle specific.
3. Using scan tool, open one of the four ABS solenoids, bleed that line (wheel specific) 4 second interval of open for the flush, 20 second solenoid rest, cool down. Repeat for each wheel. Sequence vehicle specific.
4. Check firmness of brakes. Repeat from #1 if required.
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Per chance would you have a mechanically inclined friend with a good bi-directional scan tool open to barter? Six pack of beer, steaks on the grill for bribing that sort if thing.
;)
I'll admit I've been looking for an affordable bi-directional tool for carry in the truck. No dice. The bigger units are not only more capable but more spendy. Not interested in the 'ooops, accidentally lost it' possibility for a spendy unit.
Yes there appears to be a jumper tool to activate the solenoids. Somewhere. Be cognizant of the 4 seconds open, 20 seconds cool down cycle.
Cheers!