Codes pulled issues with ABS, traction control and low power

[BKB]

Hi, have a 1992 LT1 trying to get back on the road for a friend. Had issues when starting the car the ABS would cycle in park about 3 times. Then noticed if you keep your foot on the pedal stopped ABS again would cycle. Finally it set off the ABS and traction control lights and i pulled a C12 (OK) a H21 and a H35. I cant seem to find clear discriptions of H21 or H35 any help? Car is low on power so im also looking into other issues. Main issue is ABS and what to look into. I dont have any old scan tools so just using the paper clip.

Thanks
Brian

 

[toptechx6]

I'll assume you are pulling the ABS codes using the method in the link below?

C4 Corvette Diagnostic Code Recovery Techniques

My 93 FSM shows code 21 to be the RF wheel speed sensor and code 35 is the LR wheel speed sensor.
In case you were reading ECM codes by mistake, 21 is related to the throttle position sensor which might explain the lack of power issue, there is no ECM code 35.
Turning off the ABS using the dash switch should eliminate the ABS system as a cause of the low power issue.
Keep in mind the codes do NOT mean the sensors mentioned are bad, only that the controller sees a voltage on that circuit that is out of range. The proper method of diagnosis is to use the flow chart in the Factory Service Manual, if you don't have one make it a priority, it is worth the price. Don't waste your money on Haynes or Chilton.
The FSM flow chart does specify use of the Tech 1 scan tool and a dealer breakout box for ABS troubleshooting, but careful use of a multimeter can sort out most problems.
Only a few expensive aftermarket scan tools can access ABS data, your best bet is to find a used Tech 1 on Ebay, good luck.

 

[BKB]

Yes that is the way i jumped the ALDL. Thank you very much. Going to go test the wheel speed sensors now and see what i find.

 

[Hib Halverson]

First, let me correct one thing I read up above...you can't turn off ABS in a C4. You can pull the ABS fuse but there's no switch to use. You can, however, disable traction control using a switch on the dash.

It's not stated in the first post whether the two history codes, 21 and 35, are from the chassis computer or the engine module, but let's assume they are from the chassis module. The H means they're both history codes for circuit faults which means there's been a problem with those codes at sometime in the last 49 key ups but the problem is not occurring now. That the two codes are for both front wheel sensors points at a wiring and/or connections problem somewhere in the system.

To get started solving those codes, you need the Factory Service Manual for a 93 and you need to read a technical article elsewhere on this web site at:
Corvette Action Center | Tech | Stop to Match the Go - All About C4 Antilock Brakes and Traction Control

Also, you may need a scan tester but, as stated above, a lot of the ABS troublshooting can be done without one.

 

[BKB]

I shorted A & G on the ALDL to get the codes i posted. I am still replacing vacuum hoses, plugs and wires right now. Finding all kinds of problems, car does have 180k miles on it. I will be doing an alignment on the car soon so i will be able to look into the wheel sensors and wiring after lunch. I am also picking up the service manuals for the car, owner just found them. Thanks for all the help.

Brian

 

[toptechx6]

First, let me correct one thing I read up above...you can't turn off ABS in a C4. You can pull the ABS fuse but there's no switch to use. You can, however, disable traction control using a switch on the dash.

It's not stated in the first post whether the two history codes, 21 and 35, are from the chassis computer or the engine module, but let's assume they are from the chassis module. The H means they're both history codes for circuit faults which means there's been a problem with those codes at sometime in the last 49 key ups but the problem is not occurring now. That the two codes are for both front wheel sensors points at a wiring and/or connections problem somewhere in the system.

To get started solving those codes, you need the Factory Service Manual for a 93 and you need to read a technical article elsewhere on this web site at:
Corvette Action Center | Tech | Stop to Match the Go - All About C4 Antilock Brakes and Traction Control

Also, you may need a scan tester but, as stated above, a lot of the ABS troublshooting can be done without one.

Thanks for catching my mistake Hib, of course you are correct. My mind was trying to find a correlation between the ABS light and power loss issues and I typed ABS when I meant ASR.

 

[Hib Halverson]

Too many acronyms which start with "A"

 

[Schrade]

Your car, or a friend's car? What's the history of the car?

If unknown, clear ALL DTC's detailed here.

Low power could be retarded timing from ASR fault, or transmission in fault mode from another DTC.

Clear codes, run to closed loop (FULLY warmed up), and confirm DTC's.

 

[gmjunkie]

Have you Checked and Cleaned every Ground Wire/Ground Strap under Hood,on Engine and Chassis??confused:confused
If Not,Hop to it and go from there!:W:W:W
Otherwise,Your just P*ss'n in the wind!

High Resistance,or Non Existent Grounds make Electronics Do Weird Sh*t!:L