I posted this in Scan and Tune a while back, and got no help, so now I'm trying here. I keep getting the following codes, and it's to the point now that I don't even drive the car anymore!

28-TCS C1278 Service Active Handling, Service Traction Control.

Ok, no big deal, the traction control may or may not work. Thing is, this code seems to cause this code:

10-PCM P1221

This trips the check engine light, which puts me in reduced power mode. I go in, clear out the PCM code, and the check engine light goes out. I try to clear out the TCS code, and the traction control light goes out for a second, then comes right back on with the same code! If I blip the throttle, the damn PCM code comes back, and I'm in reduced power mode again!! If I play with it for 5-10 minutes, I can get the PCM code to stay off for a few minutes, then I start to drive it. The TCS light is still on, but no PCM code. I can go out and hammer on the car, and all is fine. Then, for NO APPEARANT REASON, the damn check engine light comes on, the PCM code comes back, and I'm in reduced power mode. It happens when I'm driving normal, when I'm stopped at a light, when I'm accelerating, when I'm slowing for a turn, etc. Point is, it's not like full throttle causes it. I can hammer through the gears with no problem. Then, I'll just be driving along like normal and bang, there it is.

I've replaced the TAC module, but no luck. I've checked my wiring connections, no luck. I've taken out the battery, let it sit, and re-installed it, and no luck. I'm at my wits end. I'm sure it has something to do with either a lose connection to a sensor somewhere. Sometimes hitting some bumps in the road, or slowing and turning the car seems to cause it, like the movement of the engine is causing a short somewhere.

If anyone has had a similar problem, please point me in the right direction. I haven't enjoyed my car in months, and the summer is coming to an end!!!

 

I recently had the exact same problem. I believe I was getting the same code (1278) as you but I can't remember. I had the throttle position sensor replaced. This part includes a new accelrator pedal and the three sensors that control the throttle. I beleive this is different than the TAC module. Hope this helps.

 

Greg

I feel for you!! I had the E X A C T same issue. I bet you know what it feels like to be limping along on I-95 at 6 MPH and there are UGO's and Neons passing you by beeping the horn at you! ARGGGGGGGGGG!!!

This is what I recommend! "I went to Bowling Green KY with this issue and talked to the C5 Help Desk engineers.
They were GOD's and gave me some EXCELLENT advice. Following their advice seems to have cleared up my "REDUCED ENGINE POWER" woes!"
There are 13 common chassis grounds. "I am going to include a couple of pictures of one type of ground that is the key trouble point for a lot of C5 owners! The other type are just eyelets. The connector type in the pictures are KNOWN problem areas. The Tech's told me that they have seen numerous ground connectors that have been corroded, some that have not been properly crimped from the factory and a lot that are loose or have corrosion between the chassis and the ground lug.

I recommend spraying "EACH" ground lug with PB Blaster or WD-40 penetrating oil and letting them sit over night. Then remove each ground connection and clean the lug and chassis ground area. (**NOTE**) The lugs and the nuts will be difficult if not impossible to remove without wringing off the lug! I broke off two! Not to worry as you can grind area off flat, drill a hole and install a self tapping metal screw to get you back in the ground zone. The Tech recommended that I "CUT OFF" the ground lugs that are pictured in the attachments and put all of the ground wires in in each connector in a soldered on ground lug connection. I cleaned "ALL" of grounds but I have not cut off the connectors yet. My repair efforts have so far been successful!
I also tugged on each ground wire in the problem prone connectors to make sure that it was properly connected. I believe that is what fixed my problem.

I also replaced my TAC module and my BCM. The BCM was causing other issues because of corrosion on the circuit board inside of the silver box. Have you ever have or do you have wet or damp passenger carpets and wet or damp carpet jute under layment? Please check for water and dampness. If there is or ever has been water in the passengers foot well area there is a possibility that your BCM could be giving you issues. If you have corrosion or moisture on your BCM, it will cause all sorts of very weird problems!

If you do not have a Factory Manual for your car, I can fax you a diagram of all of the ground points. Better yet, digital pictures to the rescue!

Please write back and let me know about the water/dampness question.

Before we go too deep into the EBTCM (which can be a bitch) and the wheel sensor wiring I would like you to give the ground wiring a try. Please let me know if you have a FRONT mounted or REAR mounted EBTCM.

With that info I will be able to give you the exact ground lug to try to clean and examine first!

Check out the pics and let me know if you have questions. The picture of the eyelet ground lug behind the rear wheel with the screwing it to the frame is one of the lug that busted off. The self tapping metel screw worked VERY well!

PLEASE write, or call if you need any further assistance!
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The first place I'd look is the splices where your throttle position harness was lengthened for your supercharger, I had a bad connection and got the same results as your getting.

 

P1221 is the throttle position sensor 1-2 performance. It could be a bad TAC module, bad wiring or the throttle position sensor 2.

Since you have replaced the TAC module already then you can probably rule that out. A wiring problem is somewhat uncommon but you can double check the connections on the TAC module as well as the throttle body and look for damaged wires anywhere along the harness. Most likely the problem is the sensor, which is located in the throttle body assembly.

P1221 causes the reduced power mode and could also be causing the C1278 code as a lot of TAC codes can cause other TAC codes to set as well.

 

1 vette I worked on had that code, some teeth were missing from the gear in the throttle actuator, this allowed the butterfly to move and be out of position. It took me a little while to find, because it wouldnt do it all the time. I had the air bridge off one time and caught it moving funny. Also you dont have a velocity stack in the throttle body do you?

 

Well, on the excellent advice and tech support of Bill Curlee, I undid, cleaned up, and re-attached about 5 or 6 chassis ground points. This seems to have done the trick. I did get a code once, on the second start up, but I cleared it, restarted the car, and it hasn't come back since. I drove it hard that night, and had no problems. I've started it every morning since and have had no codes. Due to the weather here I'm not driving it, but where I used to get codes on start up, I'm not getting them now. Weather permitting, I'll drive it on Sunday and really beat on it and see what happends. I'm cautiously optomistic that the problem is solved.

I can't thank Bill Curlle enough for all his help. He made himself available by phone damn near 24/7. He is a true asset to the C5 community. Thanks again Bill!

 

How did you clean them? I would like to try this. Thanks

 

I just followed Bill's advice in his post, which I'll cut and paste here:

I recommend spraying "EACH" ground lug with PB Blaster or WD-40 penetrating oil and letting them sit over night. Then remove each ground connection and clean the lug and chassis ground area. (**NOTE**) The lugs and the nuts will be difficult if not impossible to remove without wringing off the lug! I broke off two! Not to worry as you can grind area off flat, drill a hole and install a self tapping metal screw to get you back in the ground zone. The Tech recommended that I "CUT OFF" the ground lugs that are pictured in the attachments and put all of the ground wires in in each connector in a soldered on ground lug connection. I cleaned "ALL" of grounds but I have not cut off the connectors yet. My repair efforts have so far been successful!
I also tugged on each ground wire in the problem prone connectors to make sure that it was properly connected. I believe that is what fixed my problem.

 

Greg

How's your car running? The damp weather that we have been having will let you know if you solved your problem or only made a temporary repair. Drop me a line and let me know what's up.

BC