Help: Intermittent AC & Service Vehicle Soon Light - Pontiac G8 Forum: G8 Forums - G8Board.com
 
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post #1 of 8 (permalink) Old 05-07-2015, 10:30 AM Thread Starter
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Help: Intermittent AC & Service Vehicle Soon Light

Still working on figuring out what's wrong, but thought I would check in to see if anyone else has experienced this:

V6 that normally has pretty good AC, but out of nowhere I now get the Service Vehicle Soon light intermittently which simultaneously shuts off the AC.

For the times that the AC is working, it works pretty well. I've checked for leaks, checked pressures, and even pulled a vacuum on the whole system to start fresh. That part is not the issue.

The light is very intermittent and seems to have no real pattern to it, but it happens often. On a 30 minute drive, it probably comes and goes close to 10 times, but only sticks for less than 1 minute each time it happens.

A standard OBD II scanner shows no codes, and no CEL is set - just the Service Vehicle light.

Any ideas or experiences with this?
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post #2 of 8 (permalink) Old 05-07-2015, 05:20 PM
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Those few things I can see that might intermittently shutdown the compressor output and display a message, shows the wording of "Service AC System", vs your posted wording of "Service Vehicle Soon" light. So trying to figure out a possible solution to your problem has just gotten a lot harder (or maybe impossible for me at least).
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post #3 of 8 (permalink) Old 05-07-2015, 08:48 PM
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Thermostat or temp sensor, when the car senses it is heating up it shuts down the a/c.

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post #4 of 8 (permalink) Old 05-07-2015, 09:02 PM
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Possibly similar to this? Happened to one of my employees Aztek.
http://www.chevytalk.org/fusionbb/sh...hp?tid/270791/

09 panther black G8 GT
Show:19x9.5's rear w/rolled fenders, 18x9.5's front, 20% tint, trim/lense tint in progress, sub rewire, amp adj, VIM w/ dvd in gb, interior blackout in progress.
Go: spectre, hsrk, lpm, pacesetter LTs, full 2.5" cat/mid/res delete, flowmaster ABs, INTENSE tune.
97 Red GP GTP- ECM, headers, custom exhaust, ported blower, heads, TB, CAI, etc....... sold
91 GP GTP- L67 swap, tranny, headers, exhaust, ECM, and a few more.... ;-) sold
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post #5 of 8 (permalink) Old 05-08-2015, 01:00 AM
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The A/C may need to be recharged. If the pressure drops too low it will cut it off.
Just an idea and my 2 cents. Had the same prob with my Malibu and it did the same.

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post #6 of 8 (permalink) Old 05-08-2015, 07:30 AM Thread Starter
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Well, like I said: I've already pulled a vacuum and started with fresh oil and freon so that's not the problem, and it does hold a charge. I can even watch as the pressure adjusts when the system turns on and off. All is fine in that area. And of course, since my initial post, the AC has worked like a charm, and this light has not popped up again yet. That's at least 60 miles of driving with the AC on full blast in 80 degree weather with no issues...

But to the coolant and thermostat suggestion: I'm not convinced yet that that could be it. This can happen right from start up, or even if you just have auxiliary power on (before starting the engine). Yes, I know that means the ac isn't running anyway without the engine running, but I mean for the "Service Vehicle Soon" light can sometimes pop right up with a cold engine and before even starting it.

Coolant looks very good, levels are good, car never overheats, radiator fans work and sound good, and you can see the very slight needle movement when the thermostat opens up.

I mean, maybe there's still something weird going on there, but what in the coolant system could set this light? I could certainly see how a coolant and possible engine temp issue would just instantly cut AC to help avoid overheating, but with a functioning thermostat, good coolant and the right levels, could that still cause it? Maybe a sensor is bad in there anyway?

Thank you to everyone for your comments and suggestions! I'm very appreciative of any help whatsoever!
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post #7 of 8 (permalink) Old 06-07-2017, 11:01 AM
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nbortz34,

Having same issue. Did you ever find a solution of why the a/c kicks on and off and service vehicle soon message? Mine is hit and miss as well. Kicks on and off a lot on the interstate. Sometimes i noticed when i give it gas or shift down to passing gear the ac kicks back on. A/c stays on if RPMs stay up higher. I also had my system recharged and no luck. Do we have hi/low pressure sensors on the compressor or sensors on the hi and low side of the ac lines? Thinking maybe if i have a pressure sensor going bad that would explain while at higher RPM the a/c stays on because pressure is reading higher. Any help from anyone would be appreciated. Thank you
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post #8 of 8 (permalink) Old 06-07-2017, 11:31 AM Thread Starter
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I should've tracked this better, but I didn't so I'll have to go off memory. The car would randomly go 6 months without any signs of any issue, and then come back, so it wasn't easy to root cause.

In the end, it really ended up having nothing to do with the AC system itself. The cooling system was extremely intermittent for me... I ended up flushing the system at least 2x, changing the radiator cap (probably didn't need to), and changed the water pump.

After all of that, I haven't seen an issue since. With some of the oddball intermittent issues I've experienced with this car, though, I can't exactly guarantee this will solve your problem. However, the water pump is pretty cheap and extremely easy to change. Takes less time to do that than to change your oil.
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