Is PCM bad on my 2003Pontiac Grand Prix?

No, not likely. The problem started with the cooling system so that's where you need to focus. Most likely, even though you filled it "carefully" there is air trapped in the cooling system. This is extremely common. Did you bleed the air out of the system using the bleeder valve by the thermostat? Sometimes even that doesn't do it. Some say filling it with the car facing uphill (or the front end up on ramps) helps with getting the air to move up out of the engine to where it can be bled off. If all else fails you may need to have it filled at a shop that's equipped with the proper vacuum equipment for drawing the air out of the engine as the system is filled. Good luck.

Well u mseemed to be correct! I bought a new computer and in stalled it because it was very simple and we got it shipped to our house for 90 bucks after I installed it because it was in air housing real simple to get to, we drove it yesterday and pulled and while idling the fans came on and my wife and I were excited because we really like the car! So I drove into town went to bank and PO came home and pulled in yard and the damn fans would not come on!! When I bled the air the little bleeder on thermostat open and I bled it but the one at water pumped broke off and I never did bleed there, but I see that I can go below the bleeder and loosen the fitting and most likely bleed it! I will let u know!

Well I opened both bleeders only water coming out! Yesterday when I installed the new computer the car ran fine the fans came on like they were supposed to and same thing this morning going into town. But going ito town the check engine light did come on but the car ran normally until I pulled into yard! I then did what u said bleeding both ports and no air came out! I checked code on my scanner it says PO 135, 02 Sensor Heater circuit bank 1 sensor 1, what does this mean! Is that an oxygen sensor would that cause this problem with fans not coming on when A/C is off?

I don't believe a failed O2 sensor would affect the cooling system in any way. There are 2 O2 sensors on the exhaust system that help the computer manage emissions. Probably unrelated to the cooling system/fan issues. It will cause the check engine light to come on. You don't have to fix it ever if you don't have to pass emissions inspection where you live. As for the fans, if the car is not overheating they may not need to come on. The fans rarely ran in my GP so unless you're getting a high reading on the temp gauge, I wouldn't worry about it. Just keep an eye on it. I'm glad you're enjoying it. They are great cars. We had ours for 12 years and if it weren't for that unfortunate incident with the Freightliner we'd probably still be driving it.

Yea I was thinking Sam thing but on real warm days we have to turn AC on low to get the fans on or it would overheat! But other than that on not real warm days if your not in stop and go then the air flow seems to keep it cool! This one got me baffled! We received the new computer on Monday afternoon we change it out and started it, and took it for a run out in country it was a cooler day and it did not over heat we pulled in yard and sure enough the two fans came on and we were elated! I went to bank about a 15 minute run and the check engine light came on but the cr temp stayed normal so I thought the fans were working I got home open hood and let it continue to idle to up to about 230 degrees and they would not come on. I coded the ck engine lite it said same thing it did with old computerPO 135 02 sensor bank 1 sensor 1. That’s when I wrote u back! I got one and me and my neighbor put it in he had notched a long socket years ago and we got it! I connected back the neg terminal and the code was no longer there the ck engine lite was off! We let it set there idling and it purrs smoothly but it would not kick the fans on! I installed new temp control sensor, new radiator, I put a new relay in fan relay, it did something, I took it back and switched around the other two fan relays which are the same and same problem, so we changed computer it worked they came on it sat overbite next day they would not come on ck engine lite came for 02 sensor which I replaced! I am wondering if some sensors in the AC system can effect this! I am BAFFLED! Yea I really like the car nice body engine runs great good power no smoke or using oil I had the tranny rebuilt and I love the features I never ran into this ever! If u think of anything man let me know I am going to look at the electrical diagrams tomorrow!

The electrical systems in modern cars are extremely sensitive. Tiny irregularities in the flow of current throughout the car can cause all sorts of strange problems by sending false signals to the computer among other things. That's probably what's happening with the O2 sensor. A poor connection somewhere is interfering with the signal the O2 sensor is sending causing the computer to think the sensor has failed. Something similar may be happening in the case of the cooling fans as well. It might even be the same problem affecting both. The tech I use for my cars is a genius when it comes to understanding and troubleshooting electrical systems on older cars. He spends considerable time cleaning and tightening electrical connections, tracking voltage changes as he goes. He often improves or actually fixes things by going through this process although even he admits he is often simply searching for things and can't always tell for sure if a certain wire or connection is at fault. I continue to have an electrical problem in my '06 Cobalt which he can't find and which I "fix" whenever it occurs by switching my headlights to high beam. It seems to be moisture related and the extra current drawn by the high beams seems to make those 5 molecules of moisture evaporate. ?? Who knows. Also as well as the actual electrical connections in the various wiring harnesses there are multiple grounds throughout the car that are subject to aging and corrosion. They are also a common source of problem. Find all of yours, take them apart, inspect the wires, clean them and reconnect them. And of course make sure your battery is strong and its connections are clean and tight. (I should have mentioned the battery first actually) If the battery is more than 5 years old I would just go ahead and replace it. If its newer, at least load test it to make sure its in good shape. With all this said, you may want to seek out a repair shop that specializes in automotive and truck electrical systems. They have the tools and the know how to track down the sources of the sort of problems we are discussing here. Sometimes a few dollars spent on a professional is well worth the savings in time and aggravation trying to fix it yourself. I hope there's something useful in here. Let me know how it turns out.

Well today my neighbor came over and he was sitting in car with me and when I turned it off my wife was outside and she said she herd a crackling hissing noise when I shut the engine off! Me and my neighbor stood outside and she started the car and turned it off and we herd it! it is like hot going to ground making that hissing noise! We told her do it again and we decided the noise is coming from the wiring harness of the coolant sensor!! But that harness runs under either the intake manifold or a air charger attached to the intake manifold I don’t have a book on this model, it shows an earlier model the intake manifold shown in the book dosent look like mine! It looks like a air charger the throttle body is attached! Any ideas how to get that off! It has the numbers 3100 on it for the engine size. It’s a 3.1 liter 2003 Grand Prix v6. I think that’s my problem it coincides with what u just talked about! They routed those wires under there where all that heat is! I bet there is a short there! Let me know if u got any ideas if that is a type of air charger or the intake manifold and how to get it off! Thanks. Peace!

That sounds more like a coolant leak of some sort and the sizzling is the coolant hitting something hot like the exhaust manifold. If something electrical was shorting out enough to make that noise it would immediately blow a fuse or trip a breaker so while I think you may be onto a part of your problem I suspect its going to be cooling system related. First, find a source of information for your actual engine. If your public library is still open then may have a manual. Plus there are online sources and a couple of really good Grand Prix forums online where you could find guidance. The air charger you're seeing in your manual could be the supercharger which came on the 3.8 GTP models. That's what mine was. There are too many differences to make info on that engine work on yours. Intake and head gaskets were both prone to leaking on these engines. If the leak is minor it can be addressed by putting a couple of units of Bars Leak in the cooling system. I fixed mine that way and got another 5 years out of the car without having to take anything apart. (Don't listen to the naysayers who claim Bars Leak plugs your cooling system. They don't know what they're talking about. It's a proven, GM approved product that's been around for decades) Depending on which gasket is leaking (if that's in fact what's happening) You could be loosing coolant out the exhaust or into the engine, or it could be drawing air into the cooling system. You can have the cooling system pressure tested and/or do a compression check on the engine to narrow this down. Also check your oil to see if there are signs of coolant in the oil. Your cooling system needs to be sealed and free of air so it can function properly. That may or may not be why the fans don't work properly, but its imperative that any deficiencies there be addressed first. Chances are once the system is sealed so it can pressurize properly and once all the air is expelled out of it, if there is any, the fans will start to work properly.