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If your system was working correctly, the dashed lines would turn into small blocks and the harder you pressed on the brake peddle, more blocks would display like they were advancing from left to right, similar to a horizontal line graph but dynamic, giving you a visual display of the amount of braking pressure. If you make the tester that was described and for which you can find pictures if you search for them, (or see here https://www.youtube.com/watch?v=mhzkx7ymhJA) and attach the tester to your 7-way receptacle, you would get a 'TRAILER CONNECTED' message and when you stepped on the brakes, IF THE PRESSURE MODULE WAS WORKING CORRECTLY, then you would see the blocks advance left to right. That would tell you if your truck-side system were working correctly. If no advancing blocks, like heymccall says, try a new pressure switch. Doesn't cost much, very easy to do. According to ALLDATADIY, it is a .9 hour job a the dealer to change the switch, plus their cost for the switch.
 

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Discussion Starter #22
try a new pressure switch. Doesn't cost much, very easy to do.
Can you direct me to a site that will give me the very detailed steps in the bleeding of the line that may be required. I see the switch and think I would have no trouble replacing it, but I'm not so sure about what will be required after that.

Thanks for the patience of everyone toward an octogenarian who is somewhat mechanically challenged.
 

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Discussion Starter #24
OK, here is my update report. I got a headlight for $25. When hooked directly up to the ground and brake posts on the pickup recpticle this is the result:

Display: "Trailer Connected" then when the manual controller is engaged, the gain is properly shown and the moving blocks move across. The headlight is illuminated.

When only the brake pedal is engaged the display looks the same exactly, BUT the lamp is not illuminated.

Please help me to interprest this result and help me to know where to go from here.:help:
 

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The headlamp was to rule out the integrity of the trailer wiring.
Again, I believe the pressure switch is bad. Unthread the old one and thread in a new one. Then, bleed the front calipers.
I think Brian has your answer. It takes the rest of us a little longer to arrive at the same conclusion. Slow learners, I guess.
 

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When manual apply is done, more blocks grow on screen.
When you depress brake pedal, do more blocks grow, as you press harder? If not, the pressure switch on the master cylinder is suspect still.
 

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Discussion Starter #27 (Edited)
When manual apply is done, more blocks grow on screen.
When you depress brake pedal, do more blocks grow, as you press harder? If not, the pressure switch on the master cylinder is suspect still.
When the manual apply AND when the brake pedal is depressed, the DISPLAY is the very same. The blocks grow across as more pressure is applied. The display seems to be entirely in sync with the amount of pressure either by the pedal or by varying the movement on the manual.

NOW: the only difference is in the illumination of the headlamp. It shows progressive illumination when the manual is applied slowly. It NEVER shows any illumination when the brake pedal is applied, even though the display shows exactly the same progression of the blocks.

One small update: I was able to get a 7 way plug to wire up to the brake and ground. Everything worked exactly as the direct connection as described above.

Maybe we are making progress.

I would add: when connected to the trailer. We get none of the above. Just the static dashes. I tried it again after the above test. Same result.
 

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Do all 3 stoplamps work on the truck?
Does the cruise control work?
I can't remember which set of stoplamp switch contacts are in use, but the Rube Goldberg-esque stoplamp switch is a common failure point. On my trucks, the contacts for cruise usually die first.
 

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Discussion Starter #29 (Edited)
OK, fresh off the road test! (Pick up only, of course)

Stop lights all working normally, so is the cruise control. I had to road test because I rarely use the cruise while towing.

Thanks for sticking with me on this. I have learned a great deal already, so it has been worth the effort.
 

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This maybe a stupid question, I am not entirely familiar with this type of brake controller.
Is there a direct connection with the brake switch on the pedal? or is it wired internally in the brake circuit? The brake switches are notorious for having failures and causing brake controller problems with the stand alone types.
 

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No direct connection.

To the OP, with no test headlamp illumination when using the pedal, but seeing output blocks on the cluster, is indicative of the module either needing reflashed or replaced. At this, I believe that you've diagnosed as far as you can without a scanner attached, verifying module communication. Do you have a friendly dealer nearby? You've tested all of the hardware. It's either a software or module issue.
 

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Discussion Starter #32 (Edited)
Well, I've at least learned a lot in the process and am grateful to all who responded--especially to heymccall who kept trying.

I'll just ask one final question. Do the tests we have been able to do poin to the truck rather than the trailer as the most likely source of the problem?

The relevance of that question is this: my truck dealer is in one town and my RV dealer is in another town. Neither is too far away, but it looks like I should take the truck in to the dealer rather than taking the RV. Is my reasoning correct?
 

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I don't have a truck here right now to verify your results. I'm certain the lamp will illuminate on manual apply, but not sure if it will illuminate with just the pedal. Will have to locate a truck to verify.
Yes. I believe there is a problem in your truck whereupon the TBCM is not receiving or processing a request to increase trailer brake output.
 

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And, if your dealer is skeptical about your headlamp tester, have them try it on any itbc truck, except '14 1/2 tons, and any '15s. Not sure what changed, but, it did. Odds are that your dealer may request the trailer, too, but...it's a truck side issue.
 

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Discussion Starter #35 (Edited)
heymccall, I decided on at least one more test with the headlamp so I have an update and a correction:

The lamp does illuminate when the brake pedal is pressed VERY HARD. In the earlier tests we did not press the brake pedal hard enough.

Now the result is this: The light illuminates AND the output meter at the controller is properly displayed under these conditions: any application of the manual controller, and a hard, total pressure on the brake pedal.

I know I seem like a pest, but I'm trying to do all I possibly can before taking the truck or the trailer in for service.

Right now, with the above results, I'm thinking it might be the brake system on the trailer. I had the brakes serviced right before our 2500 mile trip. The report was a broken wire to one of the wheels. We left immediately on the trip and had the brake problem on the last 150 miles just before we got home.
 

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Thinking about the pedal vs output. With headlamp based tester attached, raise trailer gain all the way up to max, then watch lamp vs output blocks. I think you'll find it takes less pressure to illuminate. Which, in turn, verifies that it is not a truck or itbc problem, but, rather, a trailer wiring issue.
 

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Discussion Starter #37
Yes, That's what I found. I have an appointment next Wednesday with the RV dealer to check out the trailer brakes.

I will report back after that to share with the community.

Thanks, mccall, for all the help.

And if anyone in East Texas need a good ITBC tester, I'll be glad to share.
 

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Discussion Starter #38
OK, I promised. Now I am here with embarrassment and almost unbelief.

The report: a bad fuse on the trailer end. The fuses were the first thing I checked both on the truck and on the trailer. In fact, I took this fuse out, checked it, and reseated it. Still, that is the report and the proof is in the fact that replacing it was the fix for my trailer brakes. When I talked with the mechanic, he told me that the fuse "looked ok, but was not good."

So, I have learned another lesson on top of all that I have learned here about the ITBC. That lesson: actually try the fuse to the brake wires even if it looks good.

The good news is that my trouble-shooting on the truck system proved to be correct. That was the first thing they ruled out at the RV shop.

Until I am in trouble again, I will be out of here unless I can be of help to someone else.
 
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