Do you think I'm throwing a C0040 RF wheel speed sensor due to different tire sizes front and back?
The reason I'm asking is because it only throws my AH/TC/ABS at approximately 70mph every key cycle! Under 70mph the car works as its supposed to.
I'm running factory size 285/35/19 firestones on the rear and BFgoodrich g force KDW up frOnt one size wider than factory 245/40/18.
I checked my wheel speed sensor plugs and harness an also replaced the front right wheel speed sensor and hub assembly.
I went ahead and ordered factory sized firestones for the front and I'll see what happens.

In the mean time... Who has some insight on what the h@$$ is going on?!!

 

Those pig tail harnesses are notorious.
Closely inspect the pins and add die-electric grease.

Steel brake lines also seem to cause this issue.

There are lots of threads and hunting for a cure for the problem you are having.

If both fronts are the same tire and the tire height is the same, I'd vote that a wider tire is not the issue.

Did the problem not exist until you changed tires?
Or has the problem occured just recently after many miles following the tire change?

 

I don't think a difference in tire sizes will make your car throw codes. I put 325/30-19's on my 05 on stock rims and didn't throw any codes. You may have a bad sensor.

 

I bought the car two months ago and it had the issue. It had 295/35/19 BFG's on the back but they were slick So i put new firestones on. I will check the pig tails again when I do the new front tires.

 

I forgot to mention that I ran jumper harnesses across the front to eliminate the sensors out of the equation. I plugged in the RF sensor to the LF harness and vise versa. IT STILL THREW A RF CODE

 

That points I the pig tail on the RF again doesn't it? ^^

 

My question is, if it's not a bad sensor and not the tire size, why does it only happen at 70+mph?

 

A wider front tire shouldn't matter.

 

Yes, it could cause a problem. The wider tire is also taller unless you decrease aspect ratio on the wider tire. Could it be that the diameter difference isn't noticable to the computer until the car speed reaches 70 MPH?

A 275/35/18 is aprx. the same diameter as a 245/40/18.

 

Can you list what size you are currently using on the front. The size you listed in your original post is the OEM size. As noted it is possible for this code to be associated with a wheel or tire change if you don't come close to maintaining the OEM stagger and rolling diameter differences.

 

255/40/18 front currently


And 285/35/19 rear

 

that front tire is only .31" taller than stock, and the diff in rolling diameter between front and back is only .15"........ i don't think thats your code prob.

 

Wolfdogs, I'm getting different numbers than you are. I'm showing a difference in diameter of .9" front to rear and a tire to tire difference of .300"

The OEM stagger is 1.2" with your new size tire you have dropped that to .9" (generally right around 1.1" wouldn't cause the problem). My recollection is that the EBCM has an allowance of 5% to accomodate tire wear. In making the change you have also changed the revolutions per mile. Above 70+ may be the sweet spot to aggrivate the wheel speed sensor calculations. Under normal circumstances with stock tires, your front tire would rotate 33 more revolutions than the rear in a mile. With your new size it is only rotating 24 times in that same mile.

 

I think he's borderline of what the computer will accept in the front/rear bias.

 

Even if the rear tire was smaller in diameter that will not cause the C0040 code. If it did he would be getting the LF wheel code as well. The diagnostics done to date indicate there is a problem in the harness going from the EBCM to the RF Wheel sensor connector. The EBCM doesn't know he swapped the wiring around so it is still calling out the RF Sensor. That automatically eliminates the wheel speed sensor and the connector on the sensor end of the circuit. It does leave the EBCM connector and the wires going from the EBCM to the RF Wheel speed sensor. It is less likely there is an issue with the continuity of the wires than there is with the connectors and their pins so the connectors should be looked at first. While the connectors on both ends of the wire harness are disconnected that is the time to check continuity through the wire. While checking continuity the wiring should be flexed back and forth to see whether or not the ohm meter detects and intermittent open or short in the wiring. You do this to see if an intermittent might be the reason why the code doesn't show up until 70 mph. So far this is just basic fault finding, look at things and make sure they are clean/making good contact, are not damaged followed by using DVM to check resistance.

The C0040 code is followed by two other characters that help isolate the fault. The OP hasn't posted that fault detail although it may be his scanner can't see those characters. Those characters indicate whether the fault is an open circuit, an open circuit or a high resistance circuit, a short to ground, a short to voltage, an erratic signal or a low amplitude (weak) signal. The DVM can be used to check for all but the erratic signal. The diagnostic procedure posted in another thread ( http://forums.corvetteforum.com/c6-t...ed-advice.html ) tells what to check and the values that should be seen at each check point.



Another reason why the code may not show up until 70 mph is a high resistance circuit due to the connectors/pins or a wire that has been damaged (crushed/pinched/partially cut through). Damage can increase the resistance in a wire. The diagnostic includes checking the wiring to make sure the resistance of those circuits is less than 2 ohms. We are talking small signal levels in these circuits and as rotational speed of the sensor increases the signal level tends to drop off to some degree. The level may be sufficient for operation in a high resistance circuit at speeds less than 70 mph but not sufficient once the car goes beyond that speed. Switching the front wheels to the rear and the rear wheels to the front so the larger diameter wheels are on the front will reduce the rotational speed of the sensor for a given car speed and theoretically raise the speed at which the fault occurs.

If the wheel speed signal is erratic that could be due to an intermittent connection or to electrical interference from spark plugs or another electronic circuit that has been added under the hood or has been moved from its proper position.

Bill

 

Ugh... I'm so tired of this mess.. My skills are pretty much maxed out here. I don't know how to test resistance and continuity...

The dealership here is as dumb as me so does anyone know a good shop in the central Texas area (Killeen, Austin, Waco) that can help me out? I want to learn this stuff I just don't have anyone around that's more experienced.

 

FT 245/40/18 = 25.72" tire height (stock)

RR 285/35/19 - 26.86" tire height (stock)

new FT 255/40/18 = 26.04"

5% for wear would mean the ECM is ok with the front tire being 24.43" tall (shorter) as it wears, but does that mean that the ECM is also ok with the front tire being 27.01" tall (taller)? That would put the operational range of 24.43"-27.01" if the 5% rulse is correct.

The OP new tire is only .31" taller, the ECM may not be ok with a tire being taller than the stock specs.

 

resistance is easy, put your meter on Ohm mode and stick the red probe in one side of the sensor and the black probe in the other. Meter should tell you what the resistance of the sensor is at that point.

Continuity is another function as well that the meter should be able to handle.

 

I'm also having an intermittent brake switch issue. C0227. So I'm ready to have a professional chase it down rather than me. Anyone heard of Corvette Warehouse in Austin? Apparently they do service

 

To check the continuity of a wire you need to put the leads from the DVM (set in ohms mode) at each end of the wire. One lead to an end. The meter will tell you if there is a circuit by measuring the resistance. Continuity is basically a very low resistance that approaches zero. An open circuit is the highest resistance you can get and it is equal to infinity. One measurement can provide you the information you are looking for on these circuits. If the resistance across the wires going from the EBCM to the wheel speed sensor is less than 2 ohms you have continuity if it is more than 2 ohms but not infinite you have a high resistance circuit if it reads infinity you have an open circuit. If you set the meter to read volts and then leave the red lead attached to the wire with the black lead moved to a good ground (frame/engine) turn on the ignition and get a voltage reading then you know the wire is shorted to a voltage somewhere. Now switch it back to read ohms. If it reads anything less than infinity you know it is shorted to ground. Pretty simple stuff. Don't give up on this stuff. If you are smart enough to hold any job above Ammo Humper (requirements:strong back/weak mind) then you can do this.

Electrical circuits are analogous to plumbing circuits. Volts are analogous to pressure, Current is analogous to the amount of water that can flow through a given size of pipe and Resistance is how much that piece of pipe impedes the flow of water through it. If you have a 1/2 inch pipe that can flow X number of gallons per hour at 40 psi and you double the pressure to 80 psi the amount of water going through the pipe doubles to 2X.

Bill