04 QX56 Rear Suspension and Sonar

[overdalimit]

I've got an 04 QX56 that I am having problems with the Rear sonar and the auto leveling suspension. I ran the diagnostics and it showed that the both controllers were bad (locatedleft side of argo area behind interior trim). I have replaced both of the controllers but neither iof these systems are working. The rear sonar button on the dash lights up as though I have disabled it and you cant get the light to go out. The rear suspension won't level itself but if you apply power to the compressor itself it'll run. Not sure if this was a problem from the factory or....... has anyone else had this problem? 12 volts power is getting to both of these controllers. Not to mention the airbag light came on one day and is justing flashing and won't go off. Any ideas ladies/fellas?

[SteveTheTech]

That sounds like you have a bit of an accessory issue.

Let's start with the rear sonar. The sonar system itself has a very strange self diagnosis procedure, rivaled only by the power liftgate self diag mode where the difference between 0.2 and 0.5 seconds can send you off in the wrong direction. As for problems with the systems themselves there are only a few problems I have seen regarding the sonar and the majority of the time it has something to do with a damaged or dirty sensor. As for the light being on constantly that indicates the system is in failsafe mode. A control unit failure code seems pretty cut and dr and I can't say I would have done anything differently.

Now for the rear leveling system I have seen a few weird things happen with these. You have to consider where the majority of this system is located...under the drivers rear of the truck. There are 4 or 6 wires in the connector, and very simple on/off sensor inputs. This system really needs Consult to test before condemning the pump device. Checking for 12v+ is not enough to justify replacement, imo. The dealer has the ability to test the height sensor although you can use an ohmmeter to measure the resistance of the sensor.

I highly suspect commonality in this issue. I am however very reluctant to offer up something as at this point it would be a shot in the dark and would most likely cost none without proof.

[C-Kwik]

I'm going off the Titan's procedure to get into the diagnostic mode for the rear sonar, but I'd imagine its the same for the QX56. Just turn the key to the on position. Wait for the light on the rear sonar button to turn off and press it ten times within 5 seconds. When I did this, my light never actually turned off as that was part of the problem so I watied a few seconds and then pressed the button repeatedly until it started to blink. Once you are in the diagnostic mode, it should start blinking the error codes. Record it and compare it to what is in the FSM:

http://www.nicoclub.com/FSM/QX56/

The correct section will probably be the Driver Information (DI) section if its arranged the same way the Titan's FSM is.

Its probably the buzzer though. Its a common problem and if the dash is anything like the Titan, you can actually access the buzzer without tools. Removal just requires a small socket. The piece is some $70 for what is nothing more than a small piezoelectric buzzer. I replaced mine with one at Radio Shack. They sell a number of them and I tried a few. The ones that have drivers are sufficiently loud, but have an audible hissing when it is not buzzing (the sonar system sends light voltage through the buzzer when off to detect the buzzer is working). You can wire it in reverse and it will eliminate the hissing but the buzzer's sound level becomes barely audible.

I found the best results with this:

http://www.radioshack.com/prod...62402

It doesn't have a built in driver though but all you need to get it to work is to attach a resistor in parallel to the buzzer and it should work. I can't recall what resistor value I used. Its not quite as loud as stock, but better than the other buzzers I tried and no hissing. When I have some free time I'll try some other resistor values to see if it makes any difference. I don't know how piezo buzzers work, but if its like a speaker, it should get louder if the overall resistance of the circuit drops. A lower value resistor would drop the resistance to a greater extent.

I've also heard of people using a computer speaker as well. Not sure what kind of specs they used, but I don't think there is a big range of differences.

Do run the diagnostics to confirm what the problem is though.