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Subaru wrx check engine light, new computer

Mechanic says the ck engine light may be due to a bad computer or old software. If they “flash” the new software and it doesn’t take, then i need to replace the computer. That’s expensive. What’s the risk of just driving with the light on? Its a 2002 wagon with less than 90k miles. It seems to run just fine. What happens if the computer goes out?

Take it to autozone or advance and get the code read for free. Report back with the code. It will be in P0300 type format.

P0304, P0302, P0301. Means misfire in the cylinder but the dealer thinks it is fake since they don’t feel it and it happens on a cold start not while running. That’s why they suggest the computer.

If the car has no driveability problems and you don’t need to pass an emissions test, drive on…If a misfire is occurring it’s pretty easy to detect…A cold start misfire could be dirty injectors…Try some Techron or 44K. Wait until you have about 1/8 tank of gas before you use these products for best results…Or determine the sensor that is sending the misfire signal to the computer and change that…I would not buy a new ECM unless the shop guaranteed it would cure the problem…

It’s a bit unclear but you state “it happens on a cold start no while running”? What happens?
CEL on or blinking? Stays on or goes out? Any stumble at all when cold?

This guy had the same problem with his 2002 WRX, and reprogramming fixed it:

I would not replace the computer as long as the car seems to be running OK. If there’s no actual misfire, there’s no possible damage to the car. If there’s a serious misfire you could damage the cat, but you would notice a misfire that bad.

Keep trying the reprogram until someone gets it right.

to ok4450- light came on & stays on. had it cleared out and it came back about a week later. normally drive 5 miles morning & night so it sits all day. This time drove 2 miles, stopped for 2 hrs, when started it again the light came on and stays on. I live in a warmer climate, 80 degree + that day. I can’t tell any difference in sound or feel of the engine. Responds well to gas & brake.

Sounds like a software problem, not a real misfire.

to caddyman know anything about “flashing” the computer. sounded like out of date software. but the “if it doesn’t take then we have to replace the computer” made me worry about having it “flashed”.

You could try the reflash but before replacing the computer you might consider things such as spark plugs and so on.
Aged plugs can cause a misfire and the perception is often that a misfire always causes bucking or rough running. That is not always the case. Some are much more subtle.

A few more questions. Does the car still have the original spark plugs and has the valve lash ever been inspected and adjusted as needed?

Have the dealer do the reprogramming. It should not result in needing a new computer.

to ok4450- platinum spark plugs (4) replace 2K miles ago. Don’t know what valve lash is. if dealer inspects as part of 90K mi service then yes it was inspected.

to jessmed1- reprograming link sounds hopeful. Everyone has told me only the dealer should do computer stuff since they are the only ones with access to all the software. know anything about reprogramming going bad?

Subaru says it is “possible” to damage the computer by reprogramming. But I assume that is only if the tech does it incorrectly. Someone else may know more about the risk of reprogramming than I do.

Reprogramming the ECM is like upgrading the BIOS in a laptop…It’s a pretty straight-forward process. This may or may not cure your problem but it should not damage the ECM in your car…it sounds like your dealership has little faith in their diagnostic and service procedures. At least they warn you upfront…Is trying another dealership an option?