Ageingrodder

Hi all, I'm new to your site but been driving my 93 Dodge W250 Cummins since 1999. My problem seems to be a common one but after reading posts and crawling all over my truck for the past 10 hours, I haven't found my answer.

The problem is the ABS/Brake lights. I suspect this is probably a coincidence, but my wife said the lights came on after see had turned a corner. In responce to some of the checks that have been posted in past posts, this is what I have done and learned so far.

1. Both lights are on steady
2. Braking appears to be normal
3. No fluid leaks
4. E-brake switch is functioning properly
5. Disconnected the RWAL unit and the ABS light goes out but not the Brake light
6. Disconnected the vacuum sensor by the hood hinge and both lights go out.
7. Vacuum gauge connected at the sensor reads about 25 inches with a dash type vac gauge. Doesn't change when brake is stepped on
8. Haven't run a smoke test, but by feel, vacuum seems to be strong on all line connected to the booster and can't hear any hissing. Then again, it's hard to hear anything over diesel noise.
9. Can't get any fault codes by shorting out the RWAL connector
10. Can't find any loose wires under dash or in rearend
11. Brake fluid level is good.
12. Disconnected RWAL for period of time did not reset lights.
13. Haven't done any recent brake work.
14. Electrical connections to vacuum sensor seem clean.
15. Cruise and speedometer seem to function properly

This is about to drive me to drinking... oh wait, too late

j_martin

When you sober up in the morning, change the bad vacuum sensor.

hope it helps.

Ageingrodder

I kind of suspected that might be the problem, but searching for "vacuum sensor" online isn't providing sources. Maybe there is a different technical part name. I'll keep looking.

NJTman

What an AWESOME First post !


Very nice

j_martin

The nomenclature is "low vacuum warning switch", or "vacuum switch"

No doubt about that being the trouble. It is closed with low vacuum, and open (like disconnected) when vacuum is sufficient. Quite simply, if disconnecting it turns out the light, it's bad.

The switch appears to be made of unobtainium. Spec is 8.5 lbs, so any commodity switch that opens between 7 and 9 lbs would work. EvilPay item 290993203894 set at 17 inches of mercury for instance.

It isn't really needed. Low vacuum is obvious with a hard brake pedal.

When it's shorted like your's is, it disables ABS.

maybe368

I found a used one on Ebay. I just used various search words and went by sight. I am not sure if it turns on the abs light though. I know it turns on the "brake" light with low vacuum. I battled this problem for a long time, finally disconnected the abs controller, the brake light still comes on with low vacuum though...Mark

Ageingrodder

Thanks a million for the information. I'm not saying I'm old, but I was driving when idiot lights were still fairly new technology. I think I will unplug it and casually search for a reasonably priced (aka cheap) used one. Thanks again

j_martin

2 items.
When anything lights the brake lamp, that also goes to the ABS controller, which then disables ABS and lights the ABS lamp.

The eBay switch I pointed out, or one similar to it, would work fine.

hope it helps.

#2isgreen

This should get stickied as the best first post ever.

In comparison to

"Hi, I'm new here, how do I get my CumminGs to smoke more?"

Good work sailor you will make a fine addition to the crew.

az2500

I've been driving CumminGs powered trucks for a little while only the second one would put out smoke. What's ups with that. Really though hope the previous post solves your problem.

Ageingrodder

You are too kind.

On a side note *** BREAKING NEWS *** This morning the lights were off. Now I know better than to think this is likely to be permanent, but I'm not going to look a gift horse in the mouth. Thanks again for the information and compliments.

KRB

Agreed!

NJTman

Yeah... YOU are so kind !