ABS code 51 - plus random disconnected wiring harness

My 99 Tacoma has an ABS light on. I connected 2 pins and it gives me the code 51.
I’ve read that this is either bad ABS ECU or a bad ground. My first thought is to clean the ground connection- can anyone confirm it’s these 2 black/white wires bolted to the fender?



This light just came on. No other person has worked on the truck in over a year, but there is a grey wiring harness that is disconnected. Can anyone tell me what this is for/if it could be related? (See image below)


Thanks
Christian

 

Yes DoubleC
Those are grounds

that 2nd grey unplugged pigtail pix is a bit too close
Pass side near fire wall?

pretty easy to trace ABS sensor harnesses….thin wires from spindle(suspension)that go up either under apron (inr fenders)or through apron
I don’t have ABS but others will know much more than me

you got code 51 from diagnostic port?
Good job!

 

thank you! Yes, i got 51 from the diag port. But no other codes. Yes the grey pigtail is pass side near firewall. It was tonight when i saw it, but that looks like it should go to a wheel speed sensor? I feel like it would have been giving me a code for that for a long time but I’ll check it out.

also I found a thread from about 9 years ago about replacing the abs ecu. Does just cleaning the ground typically help?

 

unk if cleaning grounds will solve
but
every time i have had ABS lite.....was from me working on suspension and forgetting to plug in that corner's pigtail

 

Interesting.. I don't know if that would have given me code 51 - I feel like it would have given me a code for wheel speed sensor. I'll check it out

 

agreed^^^ maybe bc 1999 diagn port not as specific as late model codes(?).....one of those sensor wires is ground

an electrical guru member might have better advice

1)find/search where tht pigtail goes
2)find locate both front abs harnesses
3)clean grounds

 

Bad ground would be really lucky. The diagnostic page for that code says bad ground, or (paraphrasing) actuate the pump with the diagnostic tool to see if it's working. I don't know how you'd actuate the pump without the tool with the light on. Without the light on, you could jamb the brakes on a dirt road to get the pump to kick on... If you find out, let us know.

 

The presence of a harness clip not connected to something doesn't mean it's disconnected. The harnesses were installed with all the options available- chances are higher than it's an unused harness than a disconnected wheel speed sensor clip- although I'd still trace the wires if possible to see where they go...

 

I added some color to make it a little easier to track. The grey clip actually connects back to a different set of wires (red) that run through a grommet in the firewall. These wires connect back into a bigger harness (purple) that includes the ones for the abs (blue). I think like Andy was saying, this is just an option that wasn’t used - maybe for like a manual trans truck. Wheel speed sensors are solidly connected.

the light went away this morning - maybe it resets after a diag port check? But hasn’t come back. I tried to loosen the ground to clean it, but this truck used to live up north, so as expected, even with penetrating oil, the tiny bolt snapped. Dremel-ed the welded nut off, cleaned the metal around the hole up and got a thru bolt and nut on there nice and tight. Will update if a code pops up again.