ABS/Brake DTC after head gasket job

[egduramax]

I started throwing an ABS/Brake Service Brake System Code after finishing a Head gasket replacement. I don't think anything is related but it is odd that it happened immediately after. Symptoms:
1. When starting/idling, not driving, no code/alert.
2. After driving between 1 and 5 miles, the ABS/Brake light come on the console and the panel reads "Service Brake System".
3. Brakes work fine
4. Antilock does not work.
5. My speedometer is over 10% off. Yes I programmed in my oversized tires. When the Hypertech reads the system settings, it reads back the correct size (24.5").

I checked the wheel speed sensors. Both measure 1015 ohms resistance and around 300 mv when I hand spin the wheels.

Not sure what else to check. Any help appreciated.
Thanks,
Craig

 

[chevyburnout1]

Best bet would be to get what code the ABS module is setting. Or we're just throwing guesses/parts at it.

 

[egduramax]

The DTC is C0245.

 

[egduramax]

Does the speedometer get its input from the wheel speed sensors or another source?

 

[Chevy1925]

Does the speedometer get its input from the wheel speed sensors or another source?

it gets its source from the back of the tcase if 4wd or back of trans if 2wd.

 

[IOWA LLY]

That code is for a mismatch between Wheel speed sensors. You have 3. One for each front wheel. And on for the rear axle. The one for the rear axle is in the transfer case, or the tail housing of the transmission if 2wd.

Since your speedometer is way off I'm going guess that the problem is coming from the rear speed sensor.

Personally I would start adjusting Tire size with your hypertech until the speedometer reads accurately and see if that cures your issue.

If you had a good scan tool you could monitor all 3 wheel speed sensors while driving and get a better idea what's going on.

Sent from my SM-N920V using Tapatalk

 

[egduramax]

That's a very helpful reply. Thanks. I was always wondering what the deal was with the rear. Thanks again. I'll let you know what I find.

 

[egduramax]

I replaced the rear WSS. No change. The speedometer is 13% off which happens to be the ratio of diameter change from stock to my tires. It seems like the ECU is accepting the tire change but the EBCM is not. Does that make any sense?

 

[IOWA LLY]

Set your speedometer calibration back to stock.....

 

[egduramax]

Well returning the tire size back to factory (31) eliminated the ABS/Brake alarm. Now what?

 

[egduramax]

Okay, now I'm really confused. I went for a drive and now my speedometer is within 4%! Very odd result. What's your wise counsel Iowa lly?

 

[IOWA LLY]

The hypertech is adjusting the speedometer calibration in the ecm.

There is another calibration in the abs module. To big of a difference between those 2 and it will cause an issue.

Now that you have the calibration back to stock, and everything is working correctly you can use your hypertech to adjust the speedometer to read accurately. I don't understand your first post though, you said you had it set for your tire size "24.5". Is that right? Or did you mean to type 34.5"?

Sent from my SM-N920V using Tapatalk

 

[Bonestock]

For some reason I have not ever neen able to set tire size to 34.5 without abs and brake indicators going off. Keep it below 34.4 and it should be good.

 

[IOWA LLY]

For some reason I have not ever neen able to set tire size to 34.5 without abs and brake indicators going off. Keep it below 34.4 and it should be good.

The abs module needs to be reprogrammed if to match the ECM. This can be done with a tech 2.

 

[egduramax]

Thanks Iowa lly. Yes, I meant to type 34.5. I'll reprogram and let you know how it goes.

 

[Bonestock]

Can a snap on versus or modis with current software program the abs or do you have to have a Tech 2?