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Code 21 & 23

Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
Check engine light went on briefly, twice. I took it for a drive and the light never came on again. Seemed to drive fine. It's been sitting for a while and I only take it out for short trips every few weeks. Anyways, I check the codes (first time doing this). When I grounded pin D&E there was a ticking that isn't present unless those two terminals are grounded. I tracked it to somewhere around the carb/air cleaner. I retrieved the codes (Code 12, 21, and 23), and started her up again. The ticking was present again for a couple seconds and then went away.

Anyways, I have the service manual. Should I worry about these? Reset the codes by unplugging the battery and see if they trip again? Does code 21 and 23 tripping together indicate something? Any advice? Oh, also I should note that the TPS has been replaced sometime in the past 7-10 years. Thanks.

-Tatortot
 
I would have to go searching to find out what the codes are...
If it is running fine,I would not worry about them....
 
Code 21 is TPS, and code 23 is Mix control solenoid (from memory). I'll reset and see what happens. Maybe running a little rough/rich (by smell), but like I said it sits a lot, and it was just idling in my garage. Thanks for the input.


-Tatortot
 
Reset the codes and see what happens, if the idle was recently adjusted that could cause either code.
 
Idle hasn't been tweaked recently.

Reset the codes and they tripped again. Started the car, warmed it up so I could take it off fast-idle. Soon after the Check Engine light went on then off 3 or 4 times, then stayed off.

I pulled the codes and this time only code 21 came up, HOWEVER, it never flashed code 12 first. Just two lights, a pause, then one more light over and over and over again. Doesn't this mean the ECM has gone bad? If it has, should I be in limp mode? Thanks.

-Tatortot
 
Okay, did some more messing around..... I unhooked the ECM from the connectors, and sprayed contact cleaner in there. Got it all buttoned back up, and no Check Engine light. HOWEVER, now I can't get code 12 to come up at all. What the heck does that mean? The repair manual has a whole test procedure to do. What would happen if the ECM went bad? Thanks.

-Tatortot

Oh, I should also add that the ECM apparently is a GM remanufactured unit. I've had the car since 1999, so it was replaced before then.
 
The ticking in the engine compartment is the mixture solenoid being activated 10 times a second. It is normal when you short the test plug and nothing to worry about.

I would clean and check the connectors again - The best electrical cleaner I have ever seen is Deoxit -- it can be found on the internet or in Radio shack stores -- far superior to the "electrical cleaner" you find in a parts store (but it is pricey). Those cleaners clean dirt from the connectors but do not do anything for corrosion -- Deoxit will bring the copper connectors back to new looking.

Not getting a 12 is a bad sign, follow the service manual. If necessary, new ECM's are available and not that expensive (under $100). Good luck and let us know how it is going.

As for what would happen if the ECM went bad -- THe carb defaults to full rich and the distributor timing will not be advanced resulting in bad gas mileage (10mpg or worse) and slugish acceleration -- other than that it keeps on running.
 
Alright, the oddities continue. Just took it out for a drive. She runs just fine. The tranny lockup jumps in and out (as it always has), so we know the computer is working. I jumped the ALDL again when I got back and still no code 12? How can it run fine, but have no code 12.... very confused. Gonna hit the books and see what to do next.

-Tatortot
 
Okay, hopefully my last update...

Went for a ride and it ran fine, as I said. Brought it home, jumped the ALDL, no code 12. Went inside, stared at the service manual, got angry. Went back to the garage, wiggled the ECM harness connectors. The upper one has the plastic lock-in broken off. Maybe something was loose? Jumped the ALDL again, and bam, normal code 12.

Took it around the block, broke the tires free, all is well. So I'm going to file this all under "if it ain't broke, don't fix it."

Still, I'm wondering why it would show a code 21 and NO code 12 before I messed with the ECM connectors. I suppose they could have jiggled loose on their own (the connector has been broken since I got the car 12 years ago), but why suddenly these problems after 12 years? Freakin' head-scratcher.

-Tatortot
 
Okay, hopefully my last update...

Went for a ride and it ran fine, as I said. Brought it home, jumped the ALDL, no code 12. Went inside, stared at the service manual, got angry. Went back to the garage, wiggled the ECM harness connectors. The upper one has the plastic lock-in broken off. Maybe something was loose? Jumped the ALDL again, and bam, normal code 12.

Took it around the block, broke the tires free, all is well. So I'm going to file this all under "if it ain't broke, don't fix it."

Still, I'm wondering why it would show a code 21 and NO code 12 before I messed with the ECM connectors. I suppose they could have jiggled loose on their own (the connector has been broken since I got the car 12 years ago), but *why suddenly these problems after 12 years? Freakin' head-scratcher.

-Tatortot
:w Tator
Well the simple answer to your question is.... You weren't ready to deal with the loose connector until you got a bit older :chuckle Sorry Tator but I just can't shake those old memories of Stingray6974 (Mike), bradfordford (Steve) and a couple others on our old chat line trying to talk you through some issues... ;LOL :happyanim: :rotfl
You got to admit, That would have been fun back then ;)

Take care son, and keep that 81 moving forward :dance :Steer :lou

Bud
aka Rare81
 
Ya kill me, Bud! I remember the chat well... I was trying to figure out why my 'vette had a high idle upon startup (don't laugh!)

You guys told me to "take off the air cleaner" and I responded with "where's that?" I could feel the :duh. And from that point on, I was known as "Tatortot."


-Tatortot
 
Glad everything is working -- I love when scary problems come with No-cost solutions.

So my question -- "Break the tires loose" Your kidding me -- My 81 can only get the slightest little squeal on a good day --have you done any mods (true dual exhast?)
 
Well, okay, a nice squeal accelerating from a stop going around a corner. Not the tire-shredding big-block torque of years past, no.

It has been slightly modified. K&N air filter, free flowing cat, quad mufflers, Edelbrock Performer intake, and who knows what else was done by previous owner(s).

-Tatortot
 

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