Electrical problem on 2000 Freightliner

[Fred Cooper]

Today the allison (6 speed) keypad began flashing the mode light, began alternating between "N" and lighting all led's in the display, and I can hear the low air pressure chime under the dash and a high pitch low volume buzzing from the allison keypad. I'm also getting a clicking and buzzing noise from the rear passenger side of the coach. The noise from the rear of the coach is coming from a transmission control relay. The relay is in a bussman 30042-0 transmission module, and the relay is an omron # 12077866 7866. It is labeled on the bussman module as the neutral sense relay. This relay is making clicking noises and simultaneously sounds like a buzzer. Replacing the relay with a spare 7866 relay produces the same results.

My symptoms are:
..with cranking batteries disconnected all is quiet
..with cranking batteries connected and ignition switch off I have a blinking mode light on the allison transmission keypad with the single display window alternating between displaying "N" for neutral and displaying every led in the window (cat eye). At the same time I am getting the low air pressure warning chime from under the dash. I'm also hearing a buzzing and clicking noise from the rear passenger side of the coach.

If I crank the engine, the allison keypad appears to work normally (blinking of mode stops, window displays gear selected normally) but the low air chime continues with (1) parking brake on and neutral selected (2) parking brake on and drive selected, (3) parking brake off and drive selected. In all instances (1, 2, & 3), the low air chime will stop if I depress the foot brake.

Since my coach is on a Freightliner chassis, I contacted the Freightliner help desk. They think it is a poor ground or poor power connector. They suggested cleaning the cranking battery on/off switch terminals, all battery terminals/connections, and the grounds to the frame rails. I've cleaned all of the above except the grounds to the frame rails. I'm still trying to find where these are located.

Anyone know where the ground connections are located on the frame rails?

Other info: Low Air Pressure chime switch was replaced in October, 2010. Freightliner help desk does not suspect this is source of problem, but I have not ruled it out yet either. Anyone know how to trouble shoot the low air pressure chime switch?

Any other ideas?

Thanks

Fred

[Perry White]

I don't think there is any air to the transmission. What model trans? 3000-4000? what year?

[Perry White]

Parking brake has air. If it doesn't have enough air can't release the park brake rite??? Park brake on alarm when putting in gear but should still go in gear.

[Martind4]

To find the ground to the chassis frame, just follow the negative battery cable to the frame. On ours, its on the passenger side (right side) almost directly behind the battery box, close to the engine. If the frame ground is really bad, I'm surprised the engine will crank normally.

Yours might be different because the coach manufacturers have the option of where to place the batteries.

[Perry White]

If all the lights are on in shifter buttons, it's either a bad ECU or low voltage to it. It sounds like a ground problem.

[Fred Cooper]

Thanks for the quick responses. I'll try to answer the questions so far:

For Perry White:
What model trans? 3000-4000? what year? I don't have the exact model number handy. It's the 6 speed allison on a freightliner chassis for a 2000 Holiday Rambler.

Parking brake has air. If it doesn't have enough air can't release the park brake rite??? Park brake on alarm when putting in gear but should still go in gear. Yes, it will release the parking brake and will go into gear.

If all the lights are on in shifter buttons, it's either a bad ECU or low voltage to it. It sounds like a ground problem. The only lights are mode button and the display window.

With engine running, the tranny appears to work correctly but still have the low air chime.

For Martind4
To find the ground to the chassis frame, just follow the negative battery cable to the frame. I'll chase this down tomorrow. I did find an illustration of the rear frame ground in a freightliner document so I'll get that cleaned tomorrow.

Thanks for the suggestions.

Fred

[Martind4]

You probably have the Allison 3000 series tranny, same as ours.

[movin-on]

There is a cheap Mexican made 125amp circuit breaker located on the frame behind the right rear wheels opposite the transmission known to fail and cause all kinds of wierd problems.... It is hard to see and on a plate with the engine air intake heater solenoid and the starter solenoid...Try jumping across it to see if your problem goes away...

[Fred Cooper]

It's fixed! If you're interested, the details are below:

Today, I found and cleaned the chassis ground, cleaned all the terminals on the starter motor, and had several more conversations with the Freightliner Help Desk.

Let me say I owe a big "Thank You" to the Freightliner Help Desk. It's nice to know there are still vendors that will talk to you and try to help when you're using their product built in 1999. Marcus and Rhonda at Freightliner were very helpful. Having attended Camp Freightliner years ago also was helpful as I had the same wiring diagrams for my coach as the helpdesk was using for diagnosis.

By wading through the wiring diagrams, we suspected a wiring short on a circuit supplied for use by the "body builder" that was getting power on a circuit that also connected to the neutral safety switch and the neutral safety relay in the transmission control module (the relay that was buzzing).

While trying to find this 6 wire circuit in the front of the coach, I discovered another relay buzzing (park brake relay) in the driver side front bay where the freightliner fuses and relays are located. The relay panel was wet. We had a bad rainstorm on Sunday and somehow water had gotten into this panel. After drying out the panel and reinstalling the relays, I still had the same problem. However, after replacing the park brake relay with another good relay, the problems went away. Apparently, the water had shorted the internal parts of the relay.

Time to change the relay 10 seconds. Time to find the problem...about 12 hours.

Obviously, I'm happier tonight than last night.

For "moving-on", I did not locate the 125amp circuit breaker, but I've filed that info away and will check it if more problems arise.

Thanks to all that offered ideas.

Fred

[Hooligan]

Fred- Thanks for the update, glad you got it fixed.
Enjoy....

[B52Guy]

Fred,
Ditto. New guy here with a '97 Holiday Rambler and just reading everything I can to spin up to speed. I much prefer to learn from others lessons, rather than having to learn the hard way.