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Low pressure light
Yesterday, we had bus out in the driveway testing high and low speed on radiator fan clutch. It tested fine by placing relay with tab 85 missing
But, in between starting and stopping and flipping chassis breakers when relay swap action, starting engine back up, low pressure light and beep came on a few seconds after starting, with both gauges registering 125 psi
Turned off motor, DOT, brake test done, everything aired back up fine,yet low pressure on, after other went offvand both gauges read 125
Any clues
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6 Replies
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This may not be relevant. On my coach I turn the key on and wait for all the check and stop engine lights to go out.
Then I engage the starter and almost instantly after starting the low pressure audible alarm beeps and then goes away.
It does this every time regardless of brake system pressures so it seems the bus system is looking for pressure, but until the pressure is verified I get the beep.
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Yes, all lights lit up on turning key. Waiting for all the usual clicks, and tach needle swing, then started her up. Al lights went out, then one low pressure light came back on with beep, gauge says its happy with full air pressure
is there a sensorvsine place we need to look at or replace
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the air pressure switches are under the front, easy to access if you can lower front bumper and it’s driver side up top, you can check terminals for power. They are just pressure switches,not sure if always open or closed. Also in front electrical compartment above there are some diodes for air alarms
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It likely has little to do with the sensor, but how the bus system processes the information and sends a signal to the dash.
Maybe the beep was intentional as a pre-trip alarm check?
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We will check under the bumper. The “beep” before always happened upon starting motor with warning lite and beep for low air oressure. Once pressure was up, lite went out and beeping stopped. This time around, after testing fan clutch with relay missing tab. Once putting everything back, we were going to do a short road trip. But… starting it up to go, before releasing parking brake to leave the low pressure lite came on with beep. Gauges ok, but didnt want to chance it, so backed bus back into garage
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I put a post on in Electrical section about a box in steer compartment that says Low Detection, I haven’t got a response yet. The older XL coaches don’t have a lot of circuit boards in them. Could this control low pressure circuit??
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