I just had a small shop with a good reputation install a z120bt in my wife's Acadia. I'm having a few issues, however.

1. The XM audio cuts out from time-to-time. The channel will show up, but there is either static or no audio at all.

2. The GPS always knows generally where we are at, but it does not place us on a road. It's like we're off-roading or something.

The XM is using an aftermarket tuner & both antenna are sitting the top-side of the dash right next to one another. I read that the 2 might be causing issues with one another. How far apart should they be & in what direction should the GPS antenna be installed? The guy who put it in has the antenna sideways as opposed to facing forward. I keep getting an error message that says G-sensor is installed incorrectly.

Please help, my wife's about to kill me!

Get the Pioneer XM tuner and relocate the antennas away from each other. Lastly is your unit installed at an extreme angle?

I have the Pioneer XM tuner. define an extreme angle? It is sitting flush in the dash, not really at an angle. Also, how far apart is far enough? Right now, they are literally touching.

About 6 or more inches would probably be a good distance.

Does having them on the dash work or should they be run to the outside of the car? Also, does the direction the sensor is facing effect the function of the GPS? Right now, it's turned sideways & I keep getting the aforementioned error message.

Does having them on the dash work or should they be run to the outside of the car? Also, does the direction the sensor is facing effect the function of the GPS? Right now, it's turned sideways & I keep getting the aforementioned error message.

The GPS antenna, if mounted on the dash, should be set on the included metal sheet. It needs a metal backplane to receive the satellite signals.

The G sensor error sounds like a different problem. The only mention of "G Sensor" in the Z120 manual is on p.199:

Oh, the orientation of the antenna (direction it is facing) doesn't matter.

But the XM & GPS issues I'm having could just be a result of the antenna's being too close together or could this g-sensor be causing some of this? As I understand it, the G-sensor just picks-up the slope the car is on

But the XM & GPS issues I'm having could just be a result of the antenna's being too close together or could this g-sensor be causing some of this? As I understand it, the G-sensor just picks-up the slope the car is on

As VBlue said, they should be separated by at least 6". That could solve some or all of your problems. If you bought this unit from this "reputable" shop, then take it back - it's their problem.

If you bought it on ebay - or grey-market, I guess its your problem, but I would first go back to the installer. First try moving the antenna apart. Should just be magnetically attached to the dash. If it is glued or something else, you paid way too much for the installation. I would guess there is enough slack in the wire to move them apart without much trouble. See if that fixes or improves your GPS issue.

I don't have XM, but if I understand the other posts, you are not using the Pioneer tuner? That could be a problem.

The G-sensor and gyro are used to approximate your position. They are all inputs to the GPS chip. So your final position will not be as reliable if you have sensor issues. Did they install VSS? If not, you didn't receive a professional installation.

You can see GPS, VSS readings. Press Home/Settings/Navi Settings/Connection Status. Speed Pulse is the VSS signal.

G sensor (incline) and gyro data can be seen on the 3D Calibration Status screen.

BTW, it takes some time for the AVIC NAV system to calibrate itself. You may want to recalibrate it by clearing the statuses for Distance, Speed Pulse, and Learning Status. See P149 in the Z120 manual. If you bough it used, you probably should do this. The sensors calibrate based on the environment in which they are installed.

I bought the unit off of ebay & had it installed. I will try moving the antenna's apart & make sure the GPS has the metal backing on the dash. Should the XM have this too? I do have a Pioneer XM tuner that I'm using. I will try the recalibration as well.

Which Pioneer tuner do you have?

I know depending on the car and such being on the dash is not good enough. I've never heard of the two canceling each other but I would rule that out I'm just saying I've had mine next to each other several times with no problems on the Z1 and Z2. The problem I was having was line of site threw the wind shield. Especially if your window isn't slanted a lot then the roof will cut the line of site and function will dip. not a positive fix for your issue but something to think about if nothing else works.. I believe it was a Grand Am and a Dodge Ram I couldn't get it to work on the dash.

Update...Moving the antennae apart fixed all the XM issues. Now the only issue is with the GPS. At times, the GPS thinks I'm off-roading & it when I slow down to stop, the map keeps moving forward & then it thinks I'm in the middle of a field. When I turn onto a different road, it realizes I've turned & then it puts me in the correct spot. This isn't typically a problem, but if my wife is driving downtown & there are lots of streets, it's an issue. Any help is appreciated! This has become one giant hassle.

For areas where gps signal is an issue, you'll need to connect the VSS wire.

For areas where gps signal is an issue, you'll need to connect the VSS wire.

Total ignorance here, but what / where is the VSS wire?

Vehicle Speed Sensor. When it's connected, the AVIC knows how far and how fast it's going even when there is no GPS signal. It's location is different on every vehicle, but you connect it to the pink wire on the AVIC harness.

Update...Moving the antennae apart fixed all the XM issues. Now the only issue is with the GPS. At times, the GPS thinks I'm off-roading & it when I slow down to stop, the map keeps moving forward & then it thinks I'm in the middle of a field. When I turn onto a different road, it realizes I've turned & then it puts me in the correct spot. This isn't typically a problem, but if my wife is driving downtown & there are lots of streets, it's an issue. Any help is appreciated! This has become one giant hassle.

Sounds like some of the sensors arent working correctly. The gyro should detect the turn, even with poor satellite reception. And VSS will tell the unit what your speed is (approximately). So the unit can do a good job figuring out your heading and speed - and approximate your position based on the last good GPS fix (dead-reconing). Did you follow my post above to recalibrate? You can also see if VSS is working. The VSS reading should be 0 when you are not moving, and non-zero when moving. Don't worry about the actual number, the HU will figure out how many tics per mile as it calibrates.

Are you still getting any error messages?

Still getting the G-Sensor error message & an error message that says the something to the extent of "the parking brake sensor is not correctly installed. Install & power down unit"

Is connecting the VSS wire something I can do on my own? I have been contemplating it. I'm sick of taking it to the shop & having them fool with it. I am more than disappointed in what I purchased. They used the Axxess adapter for unit as opposed to the PAC if that makes any difference. Also, the XM channels still show up in the driver's information center (on the dash where temperature & direction are) & the channel controls in the very back of the car don't work. Is there anyway to make either of these issues go away?