GPS/NAV Failure - 2016 Terrain - GMC Terrain Forum
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post #1 of 4 (permalink) Old 07-14-2019, 12:56 AM Thread Starter
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GPS/NAV Failure - 2016 Terrain

At the beginning of July we noticed that the Navigation system didn't show the correct mapping information. The top right of the screen shows a GPS with a line through it. We don't use the Nav very often, so not sure when this issue really started. The dealer had it for routine maintenance (oil, rotation, etc) the last week of June. I noticed the next day after we picked it up that the maps were not working and "thought" maybe it just needed to be driven around a bit more since it had been sitting in the garage all weekend. We drove from KC to STL a few days later and it still didn't work.

- Maps show me in Detroit
- GPS with a line through it on top right
- OnStar LED is still Green
- Nav Info showing 0 satellites

Any ideas on what to look at here? Where is the antenna? Where is the splitter I have read about?
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post #2 of 4 (permalink) Old 07-23-2019, 01:06 AM Thread Starter
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Nothing? Someone at least has to know where the GPS antenna is at and how the cabling is run.
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post #3 of 4 (permalink) Old 07-23-2019, 08:02 AM
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How bad does your neighborhood look? Maybe you really *are* in Detroit!

Sorry. Couldn’t resist that one.

I don’t have NAV, and I’ve got a 2011(so maybe somewhat different) - and I’m cramped for time here (gotta get to work), but my Helm Manual says the NAV antenna is the one on the roof. There are actually 2 more antennas in the rear window glass for AM/FM, and the schematic shows 2 coax cables from a “K46” Radio Antenna Module going into the radio unit.

The only thing showing up for “Navigation” in the Index (and these Helm manuals are famous for deficient Indexes ... I’ve added numerous entries of my own along the way), is for a “Navigation Signal Splitter”, which is a small box, sitting vertically, held in with 2 bolts, under the driver’s side knee bolster, above the brake pedal. The manual says “Disconnect the electrical connections”, so it has a couple of wires plugged into it.

The knee bolster is just the flimsy plastic panel held in with either 4 fasteners (Nox), or 2 fasteners (Terrain).

But personally, I think your system is working, it’s just confused as to where it is. I think you’ve got either a configuration problem (lost its “home” position), or your software got updated or needs another update (now) ... for whatever reason.

Good Luck! I gotta run ... really late now!!


There are also DTCs (OBD Codes) like "B125C" which would indicate a indicate a Satellite Antenna 1 Circuit Short to Battery, or Ground, or even an Open Circuit.

Wait ... THIS might be what it is: The "Communication Interface Module". A dealer scan tool (sorry, I know) is capable of reading the status of this module. Things like "GPS signal present YES/NO", Signal Strength (a number between 0..100, but "68" is expected, for some reason).

This module is located very close to the Splitter behind the Knee Bolster. It's a rectangular box with two bolts on one short end, and one on the other short end.

As for the routing of the antenna cable, it's depicted as coming off the antenna, going toward the liftgate, then looping back, along the roofline, on the passenger side, where it turns left, and goes through a hole above either the driver's seat or pillar between doors, then down to the dash and into the Communications Module, Splittler, and Radio.

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Last edited by Colt Hero; 07-23-2019 at 09:06 AM.
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post #4 of 4 (permalink) Old 07-23-2019, 11:53 AM
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I have had similar problems. I believe that it was water getting in, but I let the dealer sort it out. The GPS antenna is the little numb under your radio antenna. I know my dealer unscrews the radio antenna to take it through their car wash.

I had the wrong city and the GPS with a slash a few times, but more often my issue was that my location was off by about 10-100 yards. Meaning, the GPS was going the right direction, but constantly thinking I was on side streets and telling me to turn. Out on the interstate, it just didn't know what to do. Now when I take 16 hr trips, I take my old garmin as a back up measure. I never felt it was fully resolved since there was no clear cut problem and solution, but the issue has been gone for year. Maybe try unscrewing your antenna, look to signs of water, and leave it off and park in the sun. Let it thoroughly dry out. Odds are good you have some more significant wrong. I do kind of recall seeing someone else with this issue here. I think they found a TSB that there was a software glitch. You dealer should be able to check for TSBs for free.

If you google it, there was a calibration procedure for the internal compass. I think you need an empty parking lot, and drive in circles. Probably not related though, the GPS should trump the compass.

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