OBD2 code help

My daughter brought her 2010 base Cobalt home today after having the CEL lit for a couple days last week. This was when it was around zero overnight; cold for us in MD. The CEL is off now when the engine is running. When I got the codes read, the CEL was on, but only when the ignition was in the run position, and the engine was not running. The stored codes are P0573 and P0717. P0573 indicates a cruise control error, but there is no cruise control on this car. It could also indicate a brake switch issue. We checked that the brake lights work, and they do.

P0717 indicates a transmission input speed sensor error. I can’t check the wiring on the transmission easily and I’d like to wait for a warmer day to do that.

How serious are either of these errors if not attended to immediately? Remember that there is no CEL when the engine is running for either condition. She drives a mile or two to work and a similar distance to shopping or the gym.

Check your owners manual. In general, a lit CEL means check into it; a flashing CEL means shut the engine off right away to avoid major damage.

The owner’s manual addresses CELs that flash or are on constantly when the car is running. This is neither of those conditions. I read the manual before posting.

The codes are not emissions related (brakes, transmission). The owner’s manual did say that emissions related codes would keep the CEL illuminated, but did not mention other stored codes. Obviously, transmission and brake codes are stored, too.

What you said is not entirely accurate

Any recognized fault that will cause emissions to exceed a certain threshold will illuminate the mil

A fault that causes the transmission to not shift into high gear, for example, would raise engine rpms, and thus increase emissions

My statements to you are in regards to an illuminated mil, not in response to the particular codes that OP actually has

Why doesn’t the CEL remain illuminated when the engine fires up?

BTW, both codes have the note “history” on the same screen. There is a separate screen that says the P0717 is “confirmed”, but that is not the case with the P0583. Does that mean the brake code wasn’t read when polled? I suppose the ISS sensor code was read when polled.

My understanding of OBD II , the CEL is supposed to light up with the key in “on” or “run” but the engine not started. That’s so you can tell that the bulb is working. It should go out after starting the engine. If the CEL lights when the engine is running, it means the computer has detected a problem and stored a code. If later, whatever problem it detected goes away, it turns off the CEL but the prior code remains in memory. That’s done to help the mechanic diagnose any problems that may later appear. At some point absent the computer noticing the problem again the old code is erased from memory.

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The check engine light should go out after two good trips for any emissions related fault. After that, to be erased from the computers memory may occur after 255 starts.

Rather than wait for the problem to reoccur I would first replace the input speed sensor, then possibly the brake switch. When I worked on Chrysler products in the 1990’s P0717 and P0718 faults were common, the retail price of these sensors was $19.18. If they used $100 sensors like some other manufactures do they wouldn’t have this problem but there is a lot of competition in the compact car market and cost plays a role.

Relax. It’s perfectly normal for the CEL to be on when the key is in ON and the engine is not running.

Since it goes off when the engine is running, I believe it’s operating normally. The codes may have gotten tripped when the engine stalled (ask your daughter if the car stalled) and still be stored, but not indicative of an actual problem. The fact that you’re showing Cruise Control codes and the car doesn’t have cruise control supports this theory.

I’d clear the codes and see if they return. If they don’t, I’d consider the codes to be false codes. An ECU won’t store fault codes when the engine is starting, but it can store false codes if the engine stalls.

I’m relaxed, but concerned that the codes indicate a transmission control module problem. I want to be prepared if this stuff occurs again. A sensor problem will show up later and won’t cause the car to stall. BTW, the CEL was on for two days before it went off. Maybe that was the reset cycle.

I sincerely hope that’s all it was.

It’s been a reliable car for us since I bought it in 2012.


Hope you can solve this little niggle w/o major complications. I like the look of that 2010 Cobalt. The 2010 looks better than the new model imho.

If the light went out and the codes are in history then don’t worry about it. It was a fluke. If the light comes back on then you can worry. The cruise control code is unimportant and the transmission code would have to be fixed but won’t stop the vehicle from running since it has other sensors the computer can use to compensate for the loss of the speed sensor…such as the TPS. With OBD II systems if one sensor goes out the computer compensated by using other input signals. There are exceptions. Like if the crank sensor goes out your car won’t start or if the MAF sensor goes bad then it may run but very poorly