I have a 1991 F150 Custom with the 5.0, 2wd, auto trans. My check engine light came on. I flashed the codes, key on, engine off and got 11 and 15. I flashed with engine on and got 33 and 77. Does the code 15 indicate the PCM needs to be replaced? Any help would be greatly appreciated. I gave the codes via video to a mechanic and he said it was the AIC. I cleaned it, still same codes.

Thanks in advance.

 

Code 11 indicates a system pass.
The code 15 indicates a Keep alive memory test failure
The keep alive memory is interrupted when power is lost to the computer. check all connections.
Sometimes the multiple pin plug that goes to the computer could have corrosion on some of the pins.

Code 33 indicates an EGR problem where opening has not been detected. Could be EGR valve or signal to open EGR valve or sensor on top of EGR valve is defective.
If nothing has been disconnected or eliminated , the sensor on top of the valve was the most common problem there.

Code 77 indicated an operator error , WOT not detected

Different steps may be required before any tests are run. The better thing to do is to erase all codes and see if any return.

 

Thanks. I will check the computer plug connections for corrosion.

As for the 77, I did floor the gas after the single flash. I didn't understand why I got that code, unless it was an issue with the PCM. The truck runs great, just getting the engine light.

This was my dad's truck snd it sat for 15 years. I got it up and going about a year ago, and it runs great.

Thanks again,

Jon

 

I wouldn't jump to any conclusion and hurry to replace a working computer. Most of the time we rule out everything else before contemplating a computer replacement.

 

I removed the plug on the PCM and scrubbed it with a tooth brush. I did not see any corrosion on the pins and used a very light coat electrical grease in the pins. I probably wiped to much off before plugging it back in. I got the same codes.

It has been sitting with the negative terminal off since yesterday afternoon. I hope to reconnect it and go for a ride this afternoon and see if the light comes back on. I spoke to a guy that has a OBD 1 reader, but he doesn't know how to use it. I figured I would give it a shot if the light comes back on and I get the same codes.

Thanks again for your help.