EXHAUST BRAKE PROBLEM

Is your cruise control off. Sometimes that will affect the exhaust brake.

wolf10 In the number 3 scenario the tranny does not downshift, which still leaves open the throttle break switch as a possible culprit. That what makes this thing so confusing.

Since the transmission is downshifting normally, the circuit is fine all the way to the transmission, From there the electrical signal at the air solenoid needs to be checked. Set up a test light or voltmeter so that someone can see it while you drive.

If the light/voltmeter indicates the solenoid is getting 12 VDC when the brake engages. then you know you have a mechanical issue with air cylinder or exhaust brake. If not, you need to get the schematic and find out between Allison ECM and exhaust brake solenoid where the signal is lost.

JimM68. When the two functions take place, I can feel each one.

Mtrumpet, Under what happens, 1. trans light goes to 4. 2 Trans lite goes to 4. 3 trans lite doesn't change and stays at 6.

need more info.

exhaust brake switch on, foot off gas, trans selector should immediately indiate 2?

RPM permitting, trans should downshift, bringing rpm up to perhaps even near 3000?

Exhaust brake should close, further slowing motorhome.

What makes you think this isn't happening?

Scott, Brake won't engage at idle.

FRIZBEE1 wrote:
What happens 1. Everything works normal. 2. Tranny downshifts but exhaust brake won't engage. 3. Nothing happens.

Just to clarify, are you saying that the number on the Tranny control indicates the target gear? (I believe that most are defaulted to "2"). If yes, then the problem could be more than a bad switch. When my switch went bad, the tranny control wouldn't even indicate the downshift gear. It was just as if the exhaust brake was turned off.

This same exact thing happened to me a couple of years ago. It turned out to be a bad Exhaust Brake Switch. Replaced the switch with a new one from Newmar, and problem solved. At Spartans' suggestion, I checked it by removing the switch and jumping the wires (bypassing the switch). The exhaust brake then worked fine, proving the bad switch.

You can certainly run without the exhaust brake. Just make use of manually downshifting with the arrow keys on your tranny when needed. Not as efficent as the exhaust brake of course and will require more attention to rpm's and speed, but it can be used to assist with slowing the coach. You won't hurt anything (the tranny computer won't allow it.) Heck, trucks had run for years without engine brakes.

When mine went out, I was a couple of hundred miles from home. No big deal. In fact, when I took my road test for my "R endorsement", I wasn't even allowed to have the exhaust brake turned on.

So the EB turns on at idle if you engage it?