Testing Brake System Resistances?

[Jyosua]

Is it possible to do this without a breakout box? If so, how do I do this?

 

[OneLever]

Could you clarify what you mean by brake resistances? Do you mean across the coils that make up the 4WABS sensors near the tone rings?

 

[Jyosua]

Well, in the manual, the parts labeled are Hydraulic Unit Connector and Anti-Lock Brake Control Module Connector.

To clarify further: I made a thread a few days ago about DTC C1210. A few responses told me to replace the HCU. I happened to finally get my OEM Service Manual in the mail, and wanted to see about following the steps to troubleshoot for that DTC, but it seems to require a breakout box.

I was thinking it might be possible to buy an adapter, and do some clever wirestripping and soldering to get the same effect. Failing that, do you know where to get a cheap breakout box from?

 

[OneLever]

Two questions:

1. What is your level of experience with electronics?

2. You have the two volume shop manual. Did you also get the Electrical and vacuum troubleshooting manual?

I am very interested in breaking down the HCU and 4WABS Control module. But I won't have a good deal of free time to do so for another three weeks. Since we have the exact same vehicle we should have the same systems to work on.

 

[Jyosua]

I'm actually a Senior in the undergraduate Electrical Engineering program at my college. Granted, there's still quite a bit I have to learn, but I feel very comfortable with working on most electronics circuits. The main issue with the ABS stuff is that the circuit diagrams are different from the symbols I'm used to, with the exception of diodes, inductors, caps, and a few other things. That may be because I haven't taken my Electromechanical systems class yet though...

As far as the manual, no, I didn't get that one. I thought there was only 2 - didn't realize there was a third.

Either way, I won't be able to actually pull anything apart until 2 weeks from now myself. I can do simple testing until then, but before that, I don't want to risk being without a ride during the last two weeks of the semester (Last week of school and finals week). In the meantime, I'm doing as much research on this as I can, until then.

 

[budwich]

Well unless you are doing this for some sort of "course work", the cheapest and quickest "breakout box" is a "simple pin probe". It will allow you to measure resistance and voltages (waveforms or otherwise) readily without "disturbing" the wiring or the overall system.

 

[Jyosua]

Nah, not for coursework, just for myself.

I was thinking that, but for the sections in the manual that say to use the breakout box, it doesn't actually tell me what parts of the circuit I'm measuring resistances on. If I knew that, I'd be able to do it easily without the box.

For clarification, it says Breakout Box Pins 17, 15, and then chassis ground (The body of the car counts for that, right?).

 

[budwich]

Ford or any other manufacturer is only going to "recommend using a well defined tool or piece of equipment"... their liability against the "uninformed" is at stake. "Practical experience" will give you an "alternative".

A ground has to be a GROUND for testing purposes and your "training" should tell you that you need to verify that indeed a ground is a ground. A chassis may/should "qualify" but it should be verified to be sure.

BUT I don't think you understand what a "pin probe" is... its a simple stick pin "pushed" in the cable on any wire(s) that are accessible... you don't go into the circuit or box for that matter. I am probably confused as to what kind of "resistance" do you think that you are measuring???????

 

[Jyosua]

H1 CHECK VALVE COIL, CIRCUIT 498(PK) AT THE ABS MODULE

Measure the resistance between breakout box pins 17 and 15.

Is the resistance between 3 and 6 Ohms?

Yes - > Go to H5
No - > Go to H2

Essentially, the instructions are asking me to test the thevenin equivalent resistance of circuit 498(PK).

The process you are describing is called back probing, which I am familiar with to a degree.

Measuring resistance using an ohmmeter works like this: The Ohmmeter provides a very small voltage, and then uses the current drawn by the circuit to calculate the equivalent resistance of that circuit. As long as the vehicle is not on, back probing should give good results. The main issue is which connections are actually connected to Breakout Box pins 17 and 15.

Edit: Actually you're describing normal pin probing, which I don't want to do. I would like to avoid poking holes in my shielded cables in my car ~_~ They're shielded for a reason. Back Probing would be better.

 

[OneLever]

Very cool! I'm glad someone of your background has taken an interest in this. Buy an Electrical and vacuum troubleshooting manual (EVTM) off ebay for your year specifically (1997). Mine came with my shop manuals as a set. There is also a Powertrain Control/Emissions Diagnosis Manual that gives you things like fuel pressure specs which is much harder to get a hold of.

The EVTM will give you a complete pinout for the 4WABS Control module and the HCU. Using that and the shop manual to describe how the system works I believe it is entirely possible to reverse engineer the system. As a practical matter I think this can be done with a multimeter and brake line pressure tester. The breakout box can be made using test leads, a perfboard, and some switches.

From what I understand all three, two in the front and one on the rear differential, ABS sensors sit next to tone rings. They are inductive sensors supplied a low level voltage, and as the teeth of the tone rings pass by a frequency directly related to wheel speed is produced. This waveform can be analyzed with an oscilloscope.

When a wheel is sensed to be locking up (frequency decreases below a threshold) the HCU closes a normally open solenoid valve within it reducing fluid pressure being applied to the wheel in question. There are more actions performed after this but I haven't read that far yet. There is also an accelerometer somewhere near the driver's seat which is used to determine if the low frequency threshold is being met under a violent deceleration scenario or just gradual braking.

 

[Jyosua]

I had a bit of a hard time finding one, but I found an EVTM for about $20 including shipping.

It won't get here for about a week though.

Now to get ahold of a nice, but cheap multimeter. I know, it's lame that someone in an EE major doesn't even have a multimeter, but my schools have always just had them in our labs. I have some nice leads for one though.

 

[waskly]

I had a bit of a hard time finding one, but I found an EVTM for about $20 including shipping.

It won't get here for about a week though.

Now to get ahold of a nice, but cheap multimeter. I know, it's lame that someone in an EE major doesn't even have a multimeter, but my schools have always just had them in our labs. I have some nice leads for one though.

cheap dvom are just that.

you want a good dvom and then it can still lie to you.

 

[Jyosua]

cheap dvom are just that.

you want a good dvom and then it can still lie to you.

By cheap, I mean used.

 

[OneLever]

Don't go too cheap...I had a $15 Equus low end one that didn't work at all. I admit that I might have fried it by switching through the ranges with a voltage connected, but I pay attention to that now. I'm currently using a low end Craftsman multimeter of course there are better models. I'd get one with the minimum features of a continuity test, diode test, and at least 10 A DC current capabilities.

 

[Jyosua]

I was going for a Fluke 73III. I've used it many times before, and I love them.

 

[waskly]

i like the 83's more i think they are better rms

 

[Jyosua]

i like the 83's more i think they are better rms

I may end up shelling out some savings for a 179.

 

[budwich]

Your "precautions" about the "probing" the wire(s) is admirable... but again, what are you looking for??? I doubt that "pricking" a shielded wire is going to cause any harm as most shielding isn't completely solid anyway. Having said that, if you are looking at a "few ohm" resistances, it is unlikely these are "high bandwidth connections" where shielding will be the ultimate issue. More likely solenoid driver voltages / circuit... although you were referring to an HCU but then appear to speaking about the ABS control module as oppose to the hydraulic unit. Anyways, good luck in your exercise, hope you find your issue.

 

[waskly]

Your "precautions" about the "probing" the wire(s) is admirable... but again, what are you looking for??? I doubt that "pricking" a shielded wire is going to cause any harm as most shielding isn't completely solid anyway. Having said that, if you are looking at a "few ohm" resistances, it is unlikely these are "high bandwidth connections" where shielding will be the ultimate issue. More likely solenoid driver voltages / circuit... although you were referring to an HCU but then appear to speaking about the ABS control module as oppose to the hydraulic unit. Anyways, good luck in your exercise, hope you find your issue.

you dont want to break shielding on a wire, it will corrode.

i have fixed more then a fair share on cars. from people who pricked the wire now they have a problem a year later.

 

[Jyosua]

you dont want to break shielding on a wire, it will corrode.

i have fixed more then a fair share on cars. from people who pricked the wire now they have a problem a year later.

That's why I refuse to do that. XD