I have a 2006 2LT 2.4 automatic 96000 miles. This problem has been occurring intermittently for several days:

traction control light comes on and transmission shifts hard
- or -
traction control light comes on and no hard shifting and no other observable symptoms.

Sometimes the traction control light goes off after a shutdown and restart, but sometimes it does not. It does seem to clear after the car sits overnight. I think it comes on only when the engine is warmed up, but I'm not 100% sure about that.

My mechanic pulled codes today and got P0856. A web search found the following references for P0856:
P0856 Traction Control Request Circuit
P0856 Traction Control Input Signal
P0856 - Powertrain Indicated Traction Control Malfunction

Any idea how to start working towards a solution?
Thanks.

 

Glad you grabbed the code - after a quick search here, this looks like the first report on this site with that specific code.

I had a quick look on the web - and didn't see much at all - at least nothing specifically for hhr. My first thought was checking the hubs - like this suggestion for a Grand prix - 05 Grand Prix GXP P0856 code - LS1TECH

 

OK - thanks for the link. I'll take a look at the wiring at the hubs.

 

I have not had this code myself but from what I have read it's mostly comes up with a open wire to the controller or the controller it's self. They also recommend to check the controller grounds.

 

Uh, the mechanic just told you the code and gave you no other input? He is the hands on expert here we are on the internets.
A 2006 with Traction Control? Maybe my memory is slipped.

 

I'll check out the controller wiring and the controller when I get the hubs looked at and post what I find.


BTW - The mechanic retrieved the code for me as a quick favor - his shop is very busy and I didn't ask him to research it for me.

 

If it does have traction control a scantool would be able to get the ABS codes and find out exactly which hub is suspect.

 

Yes - the car has ABS.

Quick update - I got an Advance Auto scancode this afternoon. The only return was "ABS disabled."

I'm hoping to get the car into a shop tomorrow to check the hubs and ECM. In the meantime, I'd like to do a diy visual check of the ECM wiring and grounds. I don't know which underhood component it is or how to access it. Can anyone point me in the right direction?
Thanks again.

 

The scanners code readers that retail stores use do not typically have the ability to read the ABS system. That is the difference between a "code reader" and a "scantool".

The only real wires to check are the wires coming out of the hubs, they all connect to "the computer". And chase the wires.


I suspect that your hubs are worn out.

 

The traction control works by reading the speed of each front wheel and cutting back the power if one wheel turns too much faster than the other. It reads the speed by a pulse as the reluctor teeth pass in close proximity to the sensor. If the hub bearing gets a little loose, the space between the reluctor and sensor gets too big to read the speed correctly causing the intermittent problem. Sometimes rust or mud on the reluctor can interfere with the sensor but at nearly 100k miles, it is likely that the hubs could need to be replaced if they haven't been already.