All Sorts of Problems with 2007 Chevy Impala

Hi Everyone,

I had previously posted the problem quoted below, but my I have more to share on it and have brand new problems popping up with the car.

"My 2007 Chevy Impala has developed a brand new problem today. Driving down the block to the store, the speedometer started fluctuating wildly. I was going a consistent speed of about 10 mph in my parking lot and when I braked to a stop the speedometer started swinging all over the place, from 10 to 35 mph. It then gave me a message on the dash saying “Speed Limited to 107 MPH” and somehow killed my accelerator because the gas pedal no longer did anything. I restarted the car and the accelerator worked again for a bit and then pulled the same problem again. The speedometer is now fluctuating wildly the entire time I drive, including while stopped, but so far the message seems to have kicked on and disabled my accelerator only when slowing to a stop and accelerating out of a stop (it happened three times).

I know that the Impala’s governor is set to 107 mph so I can guess why that message exists, but I wouldn’t think a governor would actually kill the car even if it kicked in at the right speed.

It wasn’t that long ago that we had to have our pedal position sensor resynchronized and the mechanic had mentioned that it was possible the sensor was going bad, but I don’t think that would be the problem here as it seems like the car would actually have been accelerating sporadically, whereas in my case just the speedometer is swinging around despite an even speed."

As an update to that problem, I took the car to my mechanic (a very good mechanic, but not a GM dealership), and he could not get the car to recreate the problem and the computer was not producing any error messages. As it had happened on a night that was especially cold and with freezing rain, my mechanic suggested that the cold/damp mixture may have caused the sensors to act up. A couple of nights later, in identical weather conditions, I got the exact same problem again, but not again since then (and we haven’t had the same weather again).

Now, the car has a brand new problem in addition. After driving about a mile from our home in the car, the temperature gauge shot all the way up to highest level, the thermometer light came on, and the car began alternating messages between “ENGINE OVERHEATING/AC OFF”, “ENGINE OVERHEATING, IDLE ENGINE”, AND “ENGINE OVERHEATED, ENGINE OFF.” I might be paraphrasing a bit, but that is how I remember them.

After parking the car for a couple of hours, it ran just fine for at least a few blocks.

A few days later, we used that car again for the first time. We drove a couple of miles with no problem, and parked for lunch. On our drive back, we got the exact same messages. Now, the coolant seems to be filled up to the right level, and the engine was not actually overheating. I turned the heater to full blast and the air was cool (it was 33 degrees outside and the Impala has always taken a long time to heat up). After telling me that it was reducing engine power, the car developed an unusual engine shudder. When I parked the car and opened the hood, it wasn’t even as warm in there as it would be on a normal day after driving for half an hour. The car apparently thinks it is overheated, though, because after I shut it down, the fan continued to blow despite the keys being removed.

I should also note that during this recent event, it also started telling me to change engine oil, and is indicating that my engine oil quality is at 0%, despite the fact that it was at 31% three days ago.

I don’t know if these are related, but sense my speed sensor seems to be feeding bad information now and then and apparently my temperature sensor is feeding bad information, and possibly my oil change sensor is feeding bad information now and then, it certainly seems like something is wrong electronically.

I called GM and was told there are no recalls or bulletins for the Impala, and of course they want me to visit a dealership but offered, at best, to try to get me a bit of a discount on labor.

Anyone have any ideas?

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Did you check the radiator itself or does this car have one of those stupid pressurized remote coolant tanks? If it does hab=ve the remote tank and you can’t check the rad directly, unbolt the tank from the fender and lift it up with the cap off. If all the fluid flows into the radiator you have a leak.
Det it refilled and pressure tested.

I would suggest that possibly the Body Controller Module, PCM, or the instrument cluster has a problem. A bad output sensor on the transmission (if your car uses it to calculate speed) can cause the speedometer problem, but since you have multiple problems, I’d probably consider the electronics first.

A lot of AC ripple or fluctuating voltages can wreak havoc with vehicle electronics too. Check/clean your battery terminals, have your charging system tested for voltage and AC ripple, and look for bad grounds around the PCM and elsewhere first.

Moisture causes things to short out. @oblivion is giving great advice and that is where I would start too. Cleaning battery and ground connections. The tranny feeds the speed to the ECM which feeds the cluster. The temp sensors also feed the ECM. Since this is moisture sensitive, I’m still with @oblivion.

Doesn’t this car have a PCM (powertrain control module) and a BCM (body control module) and isn’t the PCM located somewhere in the engine compartment, like right behind the battery? I think the first thing I would do is remove the connectors from the PCM on a dry day and let them air out. They may have some trapped moisture in them.

Then I would put some silicone grease around the outside of the male part of the connector so that it is trapped between the inside and outside walls of the connector. I would not put it on the pins themselves. Then reassemble. This might work but you won’t know until you drive it in a freezing rain again.


I was wondering if you figured anything out with the overheating issue? My 06 impala had a similar experience with the temp gauge going to the top and a warning about the overheating. It also has the reduced engine power. fluid level is fine but does blow cold air at idle, heat only when driving.


That might be an air bubble in the cooling system @jacob_a_meister .

The temp going up is very likely air bubbles the cooling system. The other issue, there is a sensor behind the power steering pump (I believe crankshaft potosition sensor). Trace the 2 wires from connector to as far under the plenum as possible and you will most likely find a break or heat damage in the wires. I’m Almost certain that’s going to be your issue if you haven’t solved the problem yet. It is getting a very low or almost no connection and causing the speedometer to bounce around which in turn is forcing the tranny to shift erratically and causing your car to stall. The reason it doesn’t do it all the time is because you probably have worn motor mounts (top and bottom) and as you’re driving, the wires move around and get a better signal or lose connection. This issue will not throw a D.T.C. so your check engine light will not illuminate.

The person who started this 5 years ago never returned . They either fixed the problem or traded the thing off.

I have a 2008 Chevy Impala & am experiencing the same problem. I start my car, put it in reverse to back up, then the power to the accelerator dies & it acts like it’s in neutral. That’s when I get the error message about max speed 107 mph and my speed gauge begins bouncing around. I turn it off & back on (which so far it does fine) & I’m able to drive it as normal-except the speed gauge continues to fluctuate for a period of time after this happens. It’s mid June in Kansas so it’s not related to cold weather. It’s been several years without an update to this issue, anyone have any ideas?

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