Computer trips codes 77, 74 & 13

Mark Maxon

Registered User
I have limited access, so I will ask for your help? I have an SC that has a 2 year old engine and last week had the head gaskets replaced, It seems to be fine other than it idles like it has a cam.(rough) and it trips code 77, 74 & 13 an will not idle down. It acts like the throttle position sensor is not reporting? I have reset the computer several times and checked to see that it is plugged in and it seems to be. However is there something the guys (mechanics) did that may have damaged or knocked out of wack the Throttle position sensor when re-assembling the engine?

The shop that re-assembled it can't figure it out. It runs up fine with no miss.
sounds like a miss or rough idle, I checked all the injectors and plug wire to make sure they are connected.

I usually ask an SC buddy Sam Malone, but I lost his email address in a computer crash. If you could post or get several opinions it would be greatly appreciated.
 
77 is operator error during dynamic response test

74 R Brake On/Off (BOO) switch fault

13 O,R,C RPM at idle out of range / low


Sam Malone, is that the guy from Cheers? :)

Hmm, rough idles can be vac leaks, IAC valve, plug n wires. One time I had a horrible idle and driveability problem, it ended up being a rubber gasket inside the connector for the coil pack. I'd check all your connections, but if I were you I'd take the car back to those jokers at the auto shop and have them fix the problem they created ;)
 
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Mark,
Sent you a PM last evening. It sounds as though it could be your IAC. The other 2 codes are just test codes of items that didn't pass (which are generally operator initiated). Code 13 is the one that I would look into since it is the one that also deals with the rpm. And since you are having an idle issue...

The code description that I have for 13 is: lower rpm limit not reached...or along those lines, I'm not sure if it's "reached" or "met" or something that is nearly identical to that. Either way, it's saying that it isn't getting to it's low limit in the self diagnosis, which I would start looking at the IAC first.

(It could be your TPS, but there's codes specific to that...)


and yes, the guy from Cheers...
 
A little help here....

Code 77 is a dynamic response test that tells you to snap the throttle so to test the TP sensor and see WOT. (only seen on scanners)

Code 13 is for a lower RPM limit. The PCM looks to the programming to see if the car can idle down to the limit imposed by the PCM. If not, it will throw a code.

Code 74 is a brake switch test that means you did hit the brake during the test. Don't touch the brake pedal.

I would check the connections at tubes and such as this can cause an idle problem.

Don
 
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