I pulled a RABS code 7 (no isolate valve self test) on my '94 F150 and am having trouble interpreting the pinpoint test results. I would sure appreciate some help.

You can look at the pinpoint test procedure I'm using here if you look at figures 27 and 28.

Here's the problem: I measure 4.8 ohms between pin 13 of the module harness connector and ground. It's supposed to be greater than 10 ohms according to the procedure, with my reading indicating a short either in the wiring harness between the module connector and the RABS valve, or within the RABS valve itself. The next thing it tells me to do is to check the condition of the RABS valve connector. It looks fine; pins 1 and 3 are in good shape, solidly in place, and not corroded or bent. (I cleaned them up and repeated all this getting the same measurements, anyway.) Next I was to measure the resistance between pins 1 and 3 of the RABS valve connector itself to check for internal shorts. The normal value is greater than 3 ohms. I got 4.0, so going by that my RABS valve isolation circuit should be okay. Then, leaving the RABS valve connector unplugged, I was to check the resistance between pin 13 of the module harness connector and ground, looking for a short within the harness. There I got infinite resistance--no short--and the procedure tells me "conflict of information, repeat step 7.2" (doing a visual check of the pins for the RABS valve connector).

Obviously, I am missing something, but I sure can't figure out what it is. I tried wiggling the wiring harness from the module around at the RABS valve connector while checking the resistance to see if the short occured only with certain positions of the wiring, but it remained infinite. I can't see any indication in the wiring diagram of any source of resistance between the module and the valve, so I don't see how they can expect 7 ohms of resistance from the wiring harness, which makes me wonder if either the 10 or the 3 ohms in the procedure are misprints and leading me astray. With nothing but a few feet of wire between the module connector and the RABS valve connector, there should be negligible resistance, which would mean my readings are okay.

Any ideas would be much appreciated.

 

The procedure is clearly inconsistent with itself. It allows as little as 3 ohms through the isolate solenoid, and yet requires that the total resistance of the circuit exceed 10 ohms. This leaves any measurement between 3 and 10 ohms in inconsistency limbo.

You need to find another book, or go junkyard crawling. Find out what the normal resistance of an isolate solenoid is supposed to be.

A couple of ideas: check the resistance between pin 1 and pin 4 on the RABS valve connector (make sure the isolate and dump solenoid are not shorted to each other). It should be >6 ohms.

Now check the resistance between pin 3 and pin 4 (dump solenoid). It seems likely to me that the two solenoids would have about the same resistance. If the dump solenoid also measures about 4 ohms, you could suspect the isolate solenoid is OK, and the given procedure (the part about >10 ohms) is wrong. If the dump solenoid is something like 14 ohms then the ISO solenoid may have an internal short, and the "3 ohms" in the procedure is wrong.

 

Thanks a lot for the reply. I need all the help I can get with this one.

I looked around for another source for the testing procedure. Unfortunately, all I found so far was AllData, which is the same procedure I got off that site that ends in "zone".

I tested the resistance between pins 1 and 4 of the RABS valve and got 5.4 ohms. Between pins 3 and 4, it's 1.6 ohms. It makes sense to me that the dump side and the isolate valve would have the same resistance, but according to the already questionable procedure I'm using, in the code 8 procedure (for the dump valve) it lists a normal resistance for the dump side as > 1 ohm, so maybe the 1.6 is normal.

I checked for shorts in the module-to-RABS-valve connector by testing each of the four connections to each other and to ground, but there was no sign of a short there.

So, I'm still stuck in inconsistency limbo. I'm going to see if I can find another source for the resistance values to make sure I'm dealing with accurate info. I'm hesitant to go junkyard crawling because nothing will guarantee that the RABS valve I test is normal.

Any other ideas/information are welcome.

 

If you tell me where the pin 13 connector is I can tell you what I get for the gorund measurement. I have a 94 also. heck tell me where the other connector is too. Might as well get all the values.
Popa Tim
ps - i wont get home til after midnight...in the meantime can you remeasure pin 13 to grn with closed connector, perhaps you alleiviated the short and didn't realize it when you disconnected the connector. then with the the connector off check 2 to ground - should be open, then 1 to 2 and then 3 to 2 - all should be open again. <grin> that should keep ya busy
Popa Tim

 

Hey Popa Tim, that would be great! I don't know anyone around here who has a similar vehicle.

The module connector is behind the glove box. You have to remove the glove box to get to it. The module is about 3" x 6" and maybe 3/4" thick. The connector is on the right side of the module with a little clip you have to push down to release it facing you.

The RABS valve is inside the left frame rail directly below the master cylinder. The RABS connector is about 4" behind the RABS valve. If you find the valve you will see the wiring coming out of the back of it. and the connector is right there.

I rechecked the resistance from pin 13 to ground with the RABS connector re-connected and still get 4.6 ohms. I checked 2 to ground, 1 to 2, and 3 to 2 on the module side of the RABS connector and got open circuits on all of them.

I spent some time trying to find an alternative source for the testing procedure and struck out, so I ordered a CD-ROM copy of the Ford service manual. Hopefully that will have some info, too.

 

Makes me wonder if something went open between the rabs unit and pin13 LOL

If I don't post back tonight it means I couldnt see good enough to get it done in the dark and I'll do it in the morning.

Popa Tim

 

As best I can tell, your wiring and RABS solenoids are fine. 1.6 plus 4.0 = 5.6, near enough to your measurement of 5.4. You've also proved the wires aren't shorted to ground. It seems unlikely that the solenoids would suddenly take on an unusally low resistance -- the book is probably wrong.

 

Ok, its 5 degrees here. I'm frozen...LOL
at this temp, i'm getting 4 ohms to ground from pin 13.
Try cleaning ALL the grounds (i think there are 4 points to clean), then clearing the codes and see if it comes back. If it comes back then it would have to be internal to the Rabs unit. That troubleshooting guide you linked to does say its fused, that just might be good news!
Keep us updated. I work tomorrow too so anything you need for comparision just ask but I won't get back to you until the same time. Its tooo cold to check the valve itself...LOL

Popa Tim

 

Tim, I can't believe you offered to check your truck when it's 5 degrees out! That is way above and beyond the call! I do appreciate it.

FeFarms, I am inclined to agree that the RABS looks okay and the procedure looks wrong, but I am still stumped and hoping that CD-ROM manual gets here soon.

I will try to locate all the grounds and clean them up.

I don't blame you for not wanting to crawl under the truck in 5 degree weather. At least, not without doing it in a heated shop!

I will keep you posted on my progress.

 

My Ford Service Manual came today, and sure enough, the procedure I was using before contained a misprint.

According to the Ford manual, the normal resistance for pin 13 of the RABS module connector to ground is 3-6 ohms, not >10 like the other procedure said. The manual has already paid for itself.

That being the case, the procedure indicates that the next step is to replace the RABS module. I'll start looking around for a deal on one and let you know what happens next.

 

The replacement RABS module came today, and I just installed it. So far, so good: no error codes.

Thanks for the help.

 

Fantastic !!!!