Would you assume my ABS control module is bad?

[allmyEXes]

I bought some "seamstress" "T" pins at Walmart to poke through the wire insulation. About the same as a sewing needle. Handy little T handle on the end. Got 100 count for cheap. 100 Nickel plated T-pins

 

[John Livingston]

I've got some of those T pins around here somewhere! Thanks for reminding me. Probably would be faster, though, to just buy some more.

 

[John Livingston]

Well, not good news here. I got a second pin into the light-blue/pink wire. I get measurable resistance now between the two pins, but I still get NO continuity between either of those pins and socket 85. So, either this is the wrong wire, or there's an issue inside the socket housing. I'll try sticking some stripped wire into 85, hoping I can still push the relay in on top of it. Then I'll see if I can get 12V at pin 17. Any other suggestions?

 

[John Livingston]

Got 12V, fused, from the battery to socket 85 by just wedging the wire in with the relay. At that point, the ABS pump comes on, where it didn't before. I get a very slight voltage reading at pin 17, like 0.01V, but that's it. Seems like the next thing to do is to reattach the ABS controller's plug and see if I've still got the ABS light on the dash. If I do, I'll try one of the code readers and see if they pick up ABS data now, but I've got to walk the dog first.

 

[John Livingston]

It's tough getting old. Belay all the above about socket 85. I thought the diagram showed the socket, but it more likely shows the underside of relay, so I've looked at the opposite side, I'm pretty sure. I'll go back and start checking continuity on the opposite socket, and will let you know.

 

[J_C]

Yes the picture I posted previously was the pinout for the relay, not socket.

 

[John Livingston]

Stuck two pins back into the light-blue/pink, and I got continuity between those two, but not between either of them and any of the darned sockets. So, yeah, I've been working on what in the below image is 85a. I'll switch efforts to 85b! I will go back to the fuse panel, first. to make sure there's no joy between the neutral socket at fuse 14 and 85b! Hitherto, I'll refer to just "85", so I don't confuse any newcomers.

If I get nothing at the fuse, as expected, I'll try the wire carrying 12V stuck into the proper 85 socket and see what happens. I bet the ABS pump won't run this time!

 

[John Livingston]

Connecting 12V directly to lug 85 this time promptly blew a 10A fuse, which is the same rating as fuse 14, which hadn't blown, oddly. This is with the ignition key off.

 

[John Livingston]

Just out of curiosity, I checked and there's continuity between socket 85 and 87 and 85 and 30, but not between 85 and 86. Sadly, I'd gotten 12V at the true 85 originally, but attributed it to 86. I'm not sure why I'm not getting volts there now, but this is with a jumper pack connected, and not the real battery. I'll put the real battery back in and try again. I suppose I could've broken the strands in the wire going to 85, but that seems unlikely. The safety pins, etc., have all be fairly small.

 

[John Livingston]

Put the battery back in. Unrelatedly, I was eventually able to get continuity between 85 and the LB/P wire. The push pin was a bit rusty, and was increasing resistance, so I had to sort of scratch at it. And, while I was able to get 12V, with the ignition on, by pushing a lead into the LB/P wire, I'm still not getting anything at the genuine 85 socket (the one on the left). Seems like there's an intermittent connection in the short couple of inches between where I'm pushing in the test lead, and the socket. I'll check the pump relay sockets and see if I get any different readings there, but right now I'm only seeing, with the ignition on, 12V at 87 on the main relay. I've no idea why feeding 12V directly to 85 blew that fuse.

 

[John Livingston]

The good news is that the car still starts and runs nicely, so I haven't completely ruined it. With the engine running, I still get system voltage only at 87 on the main relay. On the pump relay, I get volts at 87, 85, and 30.

 

[J_C]

You lost me when you started calling the relay sockets 85A and 85B. There is relay contact 85, and 86.

I thought you had already confirmed that socket contact 85 was not shorting to ground, so I do not understand why the fuse blew, unless there is more wrong with the wiring than just that one wire broken, which could certainly be possible if a rodent or some other event damaged multiple wires in same vicinity. Another possibility is that the wiring diagram isn't correct for your vehicle.

Edit: Another possibility is that it isn't shorting to ground with the ignition off, but then when ignition is on, then the ABS control module is getting power on pin 20 and this is allowing its internal relay to short pin 86 to ground, and you had applied the 12V to pin 86 instead of 85.

Only other idea I have is measure the resistance of the main relay, not the socket contacts but rather the relay itself between pins 85 and 86 to verify that the relay's internal coil is not shorting out. It should have "roughly" somewhere between 50 and 200 ohms. The odd thing is, that relay coil itself should have greatly limited current to the point where the coil burnt out by the time the fuse blew, unless I am misunderstanding what you had hooked up when the fuse blew. The relay coil is only mean to handle an activation current of about a dozen mA.

Is it possible that you, or I, am getting relay contacts 85 and 86 mixed up? I suppose it's possible the fuse would blow if you had hooked up 12V direct to contact 86.

I don't mean to abandon the topic, but I don't really feel comfortable giving advice that is blowing fuses, or if it is putting that much current through the ABS control module internal relay or transistor which was only meant to handle a dozen mA, so I have no further ideas until there is something else to go on.

 

[J_C]

I just noticed something else. On the picture of the relay sockets, on the one you put arrows on to indicate 85a and 85b, is there no center 87a contact present? I don't see one, but I do on the other relay socket to the right of that one. On the diagram, that 4WABS Main Relay has 87a connecting to ground and "trailer camper adapter", so now I am wondering if that is the correct relay socket?

 

[John Livingston]

I'm really sorry for the confusion. I mentally reversed 85 and 86 early in this process, thinking your drawing was for the socket, not the relay, and I've been trying to update the data based on the using the "right" 85, which is on the left. I'll go check the center terminal. I'm pretty sure only one has that.

 

[John Livingston]

Correct. The left relay, which we've been assuming is the primary one, has NO center, 87A, socket, while the right one does.

 

[J_C]

I don't think I have a diagram for your relay box so I don't know. You might try checking for continuity between the blue/pink wire and the other relay socket? Then again, if you had been hooking up 12V to the pump relay pin 85, that shouldn't have blown the fuse either, but hooking it up to pump relay pin 86, like with the main relay, could cause overcurrent and blow the fuse since there is no (resistive) relay coil in-between to reduce current.

 

[J_C]

You lost me when you started calling the relay sockets 85A and 85B. There is relay contact 85, and 86.

I thought you had already confirmed that socket contact 85 was not shorting to ground, so I do not understand why the fuse blew, unless there is more wrong with the wiring than just that one wire broken, which could certainly be possible if a rodent or some other event damaged multiple wires in same vicinity. Another possibility is that the wiring diagram isn't correct for your vehicle.

Edit: Another possibility is that it isn't shorting to ground with the ignition off, but then when ignition is on, then the ABS control module is getting power on pin 20 and this is allowing its internal relay to short pin 86 to ground, and you had applied the 12V to pin 86 instead of 85.

I had another idea that applied to a prior post, so I have quoted that here in bold.

 

[J_C]

One way to know which contact on the ABS Main Relay socket (and determine which socket is the ABS Main Relay socket) is #85 and which is #86, is measure for resistance between ABS controller pin 19 and both of them, with resistance being nearly zero between the ABS Main Relay socket #86 and ABS controller pin 19. This is assuming the wire between the two is intact, which I'd assume it at least was at the point when the fuse blew. Hopefully the fuse blowing, saved the wire.

Edit: This is also assuming the wiring diagram and the diagram for the ABS controller connector are correct so you are sure you are testing at controller connector #19.

 

[410Fortune]

You can also pull the power box apart and access the wires from The back
Sometimes very helpful in identifying which relay is correct and that it matches the wire colors / diagram you are using

The
Bottom on the relay will
Actually say 30 85, 86 etc so you can identify which blade is correct vs diagrams (which ever way they are facing )

You guys are doing a good job
Most people would have wasted $$$ on a new abs pump by now only to find the issue is on the truck side of things

The abs light and code can take a few drive cycles to clear, when i hi ii do get the pump powered up again see if the scanner will finally communicate with it

 

[John Livingston]

Thanks for hanging in there! I'll look over these suggestions and get some info for you shortly. In the meantime, I went out just now and got voltage and resistance readings, with the ignition off and then turned on. If a box is blank, then it means there was neither measurable resistance nor voltage present. I could do this again, once, with the left relay in place, and then again, with the right relay in place, if you think that would be helpful.

A circled measurement indicates ohms.