The rear airbags are not raising the truck

Tiny
WAYNE MERTZ
  • MEMBER
  • 2002 FORD EXPEDITION
  • 0.5L
  • V8
  • 4WD
  • AUTOMATIC
  • 260,000 MILES
Rear air suspension height leveling switch getting no power. I have checked for power at the connector and found none. I have checked all fuses and have found a few that do not indicate power until you turn on the device (like the head lights). One of these fuses is #20. When the compressor does come on, I do hear the solenoids on the air bag activate but the truck does not raise. If the solenoids are activating, I would think the power must be being applied to the switch once the compressor kicks on which sounds backwards to me. I am sending a picture of the fuses that are not showing power until they are activated. All this is very confusing. Hope you can help. Wayne
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Wednesday, April 8th, 2020 AT 11:29 PM

11 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Good morning again,

As we discussed in your first post about this, these fuses power up when systems come on line.

A lot of manufacturers put fuses in the feed lines to a component after they are commanded on. There is nothing wrong with that and that is why you have no power until components are turned on.

https://www.2carpros.com/articles/how-to-check-wiring

I attached the diagram of fuse 20. It is only hot in the start position only.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Roy
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Thursday, April 9th, 2020 AT 4:15 AM
Tiny
WAYNE MERTZ
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Good Morning.

I am trying to understand the fuse #20 function in respect to giving power to the suspension system. If it is only supplied with power in the start position and not the "on" position, does that mean that it is only supplying power when the engine is running? I haven't checked for that as it would fill the shop with fumes. But I will. Thanks.
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Thursday, April 9th, 2020 AT 6:23 AM
Tiny
ASEMASTER6371
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No, power is only supplied in start position. There will be no power shown in the on position of the key.

Roy
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Thursday, April 9th, 2020 AT 6:25 AM
Tiny
BMDOUBLE
  • MECHANIC
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I think you are barking up the wrong tree. If you hear the compressor and the valves clicking at the individual airbags, the issue is with the bags. While the compressor is running spray soapy water on the bottom of the airbags, more than likely you will see big bubbles! Sometimes I can get the vehicle to raise by lifting up on the bumper or slightly jacking the vehicle because once the airbag gets past the crack in it, it will seal enough to inflate.
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Thursday, April 9th, 2020 AT 11:47 AM
Tiny
WAYNE MERTZ
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  • 13 POSTS
You are probably right, but let me try this on you (forgetting about fuse 20, etc.)
1. Will the system come on when the back end is at it's lowest point and no one in the truck? Mine does! But the back end does not raise.
2. Is the height adjustment switch in the back supposed to send a signal to somewhere tell the air compressor that the air bags need air? With the ignition off I get no power at the switch so where would I get power to the switch to tell the compressor the bags need air?
3. The compressor does come on randomly (I believe this might be for the front shocks), and the solenoids do activate at the air bags. I have not disconnected the air lines to see if air is being pumped back there yet. I will do that in the morning.
If the air bags are empty, I will not be able to make bubbles.
4. I have the truck jacked up and the height adjustment switch disconnected so I can activate it manually. Right now, I can not get the compressor to go on using the switch.

I am wondering about that relay up in front on the right side near the bumper. Some people on line say that has a tendency to fail?

Thanks for your patience.
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Thursday, April 9th, 2020 AT 7:28 PM
Tiny
ASEMASTER6371
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Okay, you are overthinking this issue.

1. Yes it does.

2. Yes, the height switch is what sends a signal to the module to turn on the compressor when the rear end is low.

3. It will come on randomly to maintain the height of the car.

4. You cannot activate it from the switch. The switch disables the system so when your car is serviced, the air will remain in the bags while the car is on the lift.

Yes, it does but if it did, the compressor would not work.

This sounds like you need rear bags. They are a common failure.

Roy
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Friday, April 10th, 2020 AT 3:49 AM
Tiny
WAYNE MERTZ
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Okay, thanks Roy.
On #4, I was referring to the Height adjustment switch/sensor in the back of the truck by the axle, not the one by the kick panel. However, I guess either could stop the truck from activating the pump.
Again, thanks for your patience with me.
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Friday, April 10th, 2020 AT 6:24 AM
Tiny
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You are welcome.

There is only one height sensor and it is back on the differential.

Always glad to help.

Roy
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Friday, April 10th, 2020 AT 6:48 AM
Tiny
BMDOUBLE
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Roy hit the nail on the head! The system will come on at predetermined amount of time if there isn't a change in the rear height sensor, and will also use the door switches as an input as well for system operation, *the self test with a scan tool will have you open and shut doors to activate the compressor by the way* Sounds like you have a classic case of bad rear bags.
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Friday, April 10th, 2020 AT 9:26 AM
Tiny
WAYNE MERTZ
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Yes, you are probably both right. I have sprayed the living daylights out of the bag with soap and water and getting no bubbles! I am at the point where I don't want to fight it anymore and will order a replacement shock kit.
Thanks guys.
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Friday, April 10th, 2020 AT 6:24 PM
Tiny
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You are welcome.

Roy
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Friday, April 10th, 2020 AT 6:26 PM

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