SES code 1661

[Ryan96WS6]

Here's the situation. Car recently out of a tune up, 2 weeks ago or about 200 miles. Tune up was because it was due at 114k miles and a slower 1/4 and drop in gas mileage. After tune up car ran better than ever before.
Untill 2 days ago. Misfires at idle and throughout the rpm most noticeable lower RPM in a high gear. Gets worse as car warms up.
Read codes at Auto Zone:
P300 obviously
P1661 According to their computer: Output circuit check signal low
Their definition: is MIL control circuit fault
Explanation: ECM detected the actual and commanded state of the driver module did not match
Probable causes: Open or short circuit condition in the driver circuit or failed or missing bulb

My question is does any of that make sense to anyone or lead you in any direction?

What I have done:
Tune up included Plugs, wires, waterpump, opti, cap/rotor.
All plugs seem to be securely connected, they are greased, don't arc in a dark area, and metal boots are gone.
ICM checked ok at Auto Zone, replaced ignition coil
Cleaned MAF

Thanks for the input

[BrdWAtti2d]

Ok if this makes sense to you it's a fault in the fault detection circuit of the PCM. In others words the computer sees a problem detecting a problem. Could just be a random code, then again it could be a PCM on the way out.

[Ryan96WS6]

Is there a way to check the PCM. I got a different PCM in a mail in tune exchange when it was tuned a year ago.
Also, the failed or missing bulb. What could that be refering to? The SES light on my car is actually burned out, and has been for a couple years. I don't imagine it is referring to that.

[BrdWAtti2d]

Yea actually it could be. The PCM has detected some kind of fault in the fault detection system. Naturally because it's a fault in the system that detects faults the PCM isn't able to say exactly what the fault is. Was it a stored code or new?

[Ryan96WS6]

Stored or new I don't know. I don't have a scanner I just go to the parts store, and I haven't had to in years. I was wondering if it is or could even be related to the misfire condition.

[BrdWAtti2d]

No, honestly the code has probably been in the system since the blub burnt out. Replace the blub and see if it goes away. Unless the PCM itself is going south, I doubt it's the source of your miss.

[Rob B (shoebox)]

Is there a way to check the PCM. I got a different PCM in a mail in tune exchange when it was tuned a year ago.
Also, the failed or missing bulb. What could that be refering to? The SES light on my car is actually burned out, and has been for a couple years. I don't imagine it is referring to that.

More than likely that is exactly what it is referring to.

[Injuneer]

According to the GM tech center code site, specific to your car:

P1661 = Malfunction Indicator Lamp Circuit Malfunction

Makes complete sense. I don't think they could make it any clearer than that. The SES light is not working. The PCM tries to turn on the light, and the voltage the PCM sees on the circuit does not match the commanded state. Bad wire, socket or bulb.

[Ryan96WS6]

I appreciate the input. Now I know P1661 has nothing to do with the misfire. Once I get that taken care I am dying to get to the track to see if I can improve my time.