New member to the GXP club

[five7kid]

Well, I don't see a lot of activity on this forum, but I may try to shake you all awake...

We just purchased a 2008 Grand Prix GXP. 89k miles, seems to run well. Body and paint are in good shape, interior decent.

Only glitch I know of so far is the power door locks don't work right - they click and try to move, but don't get the job done. I suspect a weak relay, but haven't located it yet. Trunk release works fine, not sure if the systems are related. Oh, the remote start also doesn't work (never had that feature before). I suspect some sort of alarm was installed in the past and messed these things up. I already repaired the power wire from the battery to the under-hood fuse/relay box (not the factory wire), that didn't change anything.

Oh, also doesn't have a spare. Need to look into getting one.

Didn't get an owner's manual, but found a .pdf version on line.

First order of business is fluids maintenance. Will also be checking the plugs, I'm assuming they're the factory installed. And the ATF and coolant are probably also factory fill.

Any hints or suggestions welcome.

[GTP231]

Yeah the plugs should be original yet as they're a 100K interval. If it was mine I'd just get a new set and wires since I'm in there. Coolant also will be original unless something sprung a leak. You're at 5 years might as well swap it. Trans fluid 50/50 shot on it being serviced before.
If they're trying to move you're more than likely looking at new latches for the door locks not working. The G6 etc are notorious for them.
It should also run around 13.6-8 closer to sea level once you get the hang of launching them down since I know you like checking that sort of thing

[five7kid]

Okay, now that I've actually taken it for a drive...

The door locks appear to work in the "safety" mode, locking when you take off, unlocking when you shut it off. The rear doors locked when I tried the door switch this last time, but not the front doors.

The battery is a little weak, engine turns over slowly when starting, shows 14.4 volts when running. So, may be looking at a new battery. The cable ends have been cut off and a top post battery installed, the universal clamps don't look too pure, so that alone should help.

Drives nice, nice power, really smooth idle. A little more road noise than I expected, that may be due to the tires on it, though.

It's supposed to be my wife's car, hope she gets to drive it sometime...

[five7kid]

Driving home from work after dark last night, no low beams, just high or fog lights. Turns out the relay terminals needed tweaking to make consistent contact in the fuse/relay box. It was disturbed when I was looking for the power lock relay (which isn't in that box, apparently).

My wife did drive it last night. Took it for a short drive. When we got back, the power wire to the underhood fuse/relay box was warm (remember, not the factory wire). I think it's too small, so I'm going to redo it and the battery terminals with new stuff. Still don't think that's the problem with the power locks, but it's not good.

Oh, the joys of cleaning up someone else's mess...

[five7kid]

Put a 4 gauge cable between the battery terminal and the fuse/relay box, doesn't get hot anymore. Didn't seem to change anything else, though.

Took it for emissions testing, which includes putting the car on dyno rollers. They have a lane marked "4 wheel drive and traction control", so I got in that lane. A tech came up and asked if the car was full-time 4WD, I said no, but it has traction control. Can the traction control be turned off? Yes. Okay, move over to a different lane. So, I moved over, and turned off traction control. I was pulled into the bay and told to turn off the engine, get out and go to the waiting area (normal procedure). They took forever on the car in front of me, finally pulled the GXP on the rollers. The test equipment has a hookup for the OBD II, which they did, then before clicking on "test start" on the screen, the tech started the engine and ran it up in gear. Did this several times, then clicked on "test terminated". Pulled the car off the rollers, called me out of the waiting area, handed me a hand-printed form saying traction control couldn't be turned off so they wouldn't test it.

Seems the button isn't very consistent about turning off traction control, and when you turn the car off and restart it, it defaults back to traction control on. I asked if it could be tested in the "traction control" lane, and he said "No!" quite emphatically - not sure why that would be. So, I'm not sure what to do about that, but it has to be able to be turned off before I take it back. One would first suspect the switch, removing it requires pulling the whole console, from what I can see.

Power door locks seem to work pretty well unlocking the doors when put into park (I reset it to do that), but the driver's door still is the least reliable. I really don't think it's the latches. The more you press the button, the less likely it is to click the locks. Sure seems like a problem with the power getting to the locks, which sounds like a relay problem to me.

There is also a clunking noise under the dash when hitting a bump (like driving over the curb to our driveway one front wheel at a time). I really think something was added to the car (like an alarm or stereo) and then removed, leaving something loose, and possibly something not hooked up right. Not sure when I'll have a chance to remove panels and get a look up there.

Anybody have an idea where the door lock relays are located?

One other issue - intermittent contact with the headlight relay. There was a piece of paper on one of the contacts when I pulled that relay looking for something obvious with the door locks (I didn't recognize the label the fuse/relay box had for that relay - "HDM" or something like that). I've tried tweaking the terminals sideways to improve contact with limited success. At least the headlights worked for my wife last night when she drove the car.

[GTP231]

The actuator for the locks is part of the latch assembly unfortunately.
The relay is in the interior fuse blocks at both ends of the dash I believe

[five7kid]

Thanks, I'll look there and see what's what.

[five7kid]

Well, the passenger side locks have been working fairly consistently, but the driver side not so much. So, perhaps it is just the latches. Would be a shame to have to replace them all.

Changed the oil & tranny fluid today (and filters, of course). The tranny fluid was pretty dark. The Dexron VI has a funny smell to it, so not sure if it was burnt (and I don't smell very well). Not a lot of junk in the pan, so the tranny is probably okay. I would guess the fluid had never been changed, though.

Forgot to mention that from time to time, after sitting at a light for awhile, it will not engage right away when giving it some gas, like a second, then jerk forward. I didn't check the tranny fluid level because I was planning on changing it, but it may have been low (slight leak on one of the cooler lines). We'll see if the fluid change made that go away.

Also changed the spark plugs, which were all firing, but didn't have much life left in them. That back bank is fun...

[Rob]

I have to change the tranny fluid in mine. Sure looks/smells burnt and I only have 57K miles on it. Bought it around 41K or so. No real issues with ours other than if the oil is just a tiny bit low, the lifters make noise. But keep it topped off and its quiet as can be. Weirdest thing I've ever seen.

Also have to do the anti-freeze. Not looking to change the plugs though.

Enjoy!

[five7kid]

No recurrence of the transmission glitch. I should have checked the fluid level before I changed it, so don't know if it was low, or just needed the fluid/filter changed. Seems to be working very well now. The small leak at the cooler line seems to have stopped as well.

Decided I'd try emissions one more time. If the TC button was tapped repeatedly, it would turn off. So, I told them to try that. The tech didn't appear to have any problem getting it to turn off, this is what it sniffed:




So, finally got plates. But, it's never had front plates on it before (not required in the states it's been in before), and Colorado requires front plates, so went to the dealer to get the mount. Had to get it in the next day, so I talked to the service department about the door locks while I was there. Their estimate wasn't far from what I expected, so I made an appointment and dropped it off this morning. Diagnosis confirmed the latches (although they started working pretty well last night in our 10 degree temp), they'll have it done tomorrow. That's a job I could have done myself, but this way I know the right parts were replaced, and they'll get to do the door adjustments (which I hate trying to get right). And better to be torn apart waiting for parts in their shop than my garage. They're also going to install the license plate mount.

They seemed to enjoy knowing they were going to have a GXP in the shop. Said they don't see many of them. In fact, at both the parts counter and service center, when I said I have a 2008 Grand Prix, they said, "it's not a GXP, is it?"

[GTP231]

Damn they get you both ways with emissions testing out there.
Glad to hear all is going well now with it

[five7kid]

Yes, the car is put on dyno rollers, the exhaust is collected and analyzed, and the OBDII is monitored. This is my first OBDII vehicle requiring emissions testing (my Camaros have collector plates and are exempt). The test on the rollers lasted about half a minute (we used to have an '84 full size van that took about 5 minutes to get through the test). I was impressed how clean it sniffed - the new plugs and fresh oil change didn't hurt anything, I'm sure.

[five7kid]

Updates:
The dealer replaced the door latches. When I got it back, the rear passenger door outside handle wasn't flush with the door. Took it back, they said the latch was defective, replaced it no charge. Took 2 days, though, because they had to overnight a latch in.

All 4 tires that came with the car were the same 255 width. The car followed ruts horribly. One rear tire had a slow leak, took it to the tire store. The rear tires had good tread, fronts about gone, so they put the rears on the front rims (after fixing the leak) and proper 225's on the back. Drives a whole bunch better now. The tires that came on it sound like knobby truck tires going down the road, the rears are quieter now. I'll probably go back in a month or so and get fronts to match the rears (in 255, of course). Having quiet tires will make it much nicer, I'm sure. The 225's look better on the 7" rear rims as well.

According to the on-board computer, it'll get 27 MPG on road trips, but around town only 16-17 (somebody has a heavy foot...). Not quite as good as the '95 Century it replaced, but, hey, the Century doesn't go like it does, either...

[five7kid]

I don't think I mentioned I changed the oil the same time as I changed the tranny fluid with AMSOIL OE. We've put 3000 miles on it since then, hasn't moved off the full mark. Pretty happy with that. No recurrence of the tranny glitch, probably means it was low on fluid. No drips in the garage, so must have stopped the leak.

One annoying characteristic still: When you turn on the right turn signal at night, the high beams come on. When you've made a left turn and they cancel after straightening out, the high beams come on. Sometimes takes a couple of tries to get them to go back to low beams. Hate to think what other drivers are thinking about us when that happens.