Kadorja

Car is a 2008 w/ procharger, long tubes and alcohol injection. Barely over 6k miles.

Alright so when my dad owned the Vette he rarely got a reduced engine power and service traction control message on the dash. When it first popped up he got a new throttle body and I believe accelerator pedal installed which didn't fix the issue. He said it was about a year and a half with no issues but he did get the message two or three times the 4 years he's had the car. Also as a side note the whole time he owned it he never drove her in the rain and he usually washed her down with towels and not a hose.

So now that I've had the car for only a week I've seen the message a total of three times. Twice of which where earlier today. I did wash the car with a hose but I didn't spray the engine bay down and she had ran fine all day yesterday in the hot weather.

I just want to see what I can look at and check before I try to send in the cash for my dads extended warranty (which may not transfer since he did his own oil changes) and stop by a dealership to see what their advice is. The car was rolling down the driveway in neutral when the code came on earlier today. I disconnected and reconnected the battery but before I did that I tried to read any codes but the car never had a check engine light and no codes where able to be pulled. I plan on checking all of the TB connectors and whatever else I can get my hands on. Should I clean them out with compressed air and put a little dielectric grease on them? I'm going to check for nicks and cuts as well.

It's just a pain in the butt to go from 650hp to next to nothing in a second. I pulled onto base as happy as can be and next thing I know I'm full throttle just trying to get up to 35mph. Of course I was so angry at the message I flew up on a curb when I parked her and scratched the metal bumper pieces. Thankfully no fiberglass or paint was touched.

Anyone have any idea of what else to look for?

filmjay

Was a speed sensor for me, I believe. I swapped hubs and axles a year or so ago and haven't had the issue since.

Kadorja

Good to know. I wasn't sure if the TCS was actually an issue with it or not. Hopefully the Vette tech is at the dealership tomorrow. And hopefully my supercharger doesn't eat my new belt I installed. Guess I'll know by tomorrow.

Kadorja

Well this is getting really annoying. I couldn't make it to the dealership today because I had to get my CCW Permit and the Vette tech was out for lunch before I could stop by. The reduced engine power kicked in multiple times the past few days. Sometimes it's driving at speed and other times it's after a full days worth of driving and beating her up and just pulling into the driveway.

I've started her up and the power mode pops up and sometimes just shutting her down clears it but other times I have to disconnect the battery. There just seems to be no rhyme or reason to it at all. Also I've tried it with TCS and Stability Management on and off. No luck.

carlrx7

buddy had same issue, wheel hub fixed it.

Bill Dearborn

Not sure how a wheel hub fixes a problem like this. If the hub is loose or has a bad sensor ABS, TC and AH will all be flashing. Hubs are common to all 3 functions of the EBCM so when they fail the whole thing fails. Traction Control has two parts torque reduction and brake application. If the rear wheels/wheel are spinning to much or just one is spinning the EBCM will send a torque reduction request to the ECM and the ECM responds by reducing torque and telling the EBCM that it reduced torque. If the wheels are still spinning the EBCM then can apply the rear brakes to control wheel spin.

If the ECM detects an engine code/codes that indicate that it can't control engine speed properly it sets the reduced power mode and sends a message to the EBCM that it can't perform its part in Traction Control and the EBCM sets a code of its own and lights the Service TC message. Fixing the engine problem causes the Reduced Power Mode and the Service TC message to go away.

Get a code reader that can read OBD II and ABS codes so you can see what is going on.

These are the codes you will see and the diagnostic procedure related to them:
DTC C0240 or P0856
Diagnostic Instructions
• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor
DTC C0240: PCM Traction Control not Allowed
DTC P0586:: Traction Control Torque Request Circuit

Circuit/System Description
The electronic brake control module (EBCM) and the engine control module (ECM) simultaneously control the traction control. The EBCM sends a serial data message to the ECM requesting torque reduction. When certain ECM DTCs are set, the ECM will not be able to perform the torque reduction for traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.

Conditions for Running the DTC
• The ignition is ON.
• Ignition voltage is greater than 8 volts.
Conditions for Setting the DTC
The ECM diagnoses a condition preventing the engine control portion of the traction control function and sends a serial data message to the EBCM indicating that torque reduction is not allowed. The ECM will typically set a DTC and the EBCM will set this DTC.

Action Taken When the DTC Sets
• The EBCM disables the TCS for the duration of the ignition cycle.
• The Traction Off indicator turns ON.
• The DIC displays the Service Traction Control message.
• The ABS remains functional.

Conditions for Clearing the DTC
• The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
• The electronic brake control module (EBCM) automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Code P0068 or P0121 will generate a reduce power message. They are both related to the throttle position/control circuits.

DTC P0120, P0122, P0123, P0220, P0222, P0223, or P2135 are throttle position codes and will also generate a reduced power mode.

When you get the message you should pull over and without turning the engine off read the codes. That way you get to see all the codes as they exist. Some of them go away when you turn the engine off.

Bill

Kadorja

I've tried reading the codes before but the reader we have at the house doesn't check ABS codes. I've had one instance where the check engine light came on but other than that it just tosses out the reduced power mode. I want to try to get it to a dealership when it does go into reduced power mode to see what they can find. Hopefully they can pull all the recent codes that I cant see.

filmjay

I had a faulty VSS (vehicle speed sensor) code in EFI Live. I'd had the issue before and couldn't figure it out, but I just so happened to be logging in EFIL when it happened and caught it.
I'll check and see if I still have the log, but we're talking about well over a year ago.

Kadorja

Had an appointment at the dealership at 0830 this morning. Got there and they said they wouldn't get to the car until at least the afternoon. I said screw it I'll bring it back later.

Just getting annoyed by the whole thing. Never went off this weekend even after I threw a belt. I gotta set up another appointment with them next week once I can get my roommates car for the week. That way I can just leave it with them so they can drive it possibly and see what happens.

How much is EFI live? I skimmed through their site but I'm at work and can't really check out prices or anything. Maybe I'll just do a datalog myself and see what happens.