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Discussion Starter · #1 ·
I bought a 1991 S10 Blazer a few months ago and found that the ABS unit was unplugged at all three connections. I plugged it back in and it threw the codes 21, 25, 31, 35, 63, and 66. I looked into the problem and ohm tested all wheel speed sensors at the 8 pin connector (mind you I have 4 wheel abs) and my rear left wheel speed sensor had no reading, while the other three were between 1400 and 1900 ohms (within specifications of 1k to 2k ohms). Is my EHCU bad?

Code 63 could either be brake line to ground, or the system was bled with the ignition on, which I've never done.
Code 66 says to repair other codes before looking at this one, but it reads as a poor power or ground connection at EHCU 2-way connector, and if code 65 is present instead of 66, then to attempt to clear it, but if it doesn't clear, to suspect an EHCU failure.

I am going to check my wheel speed sensor where it connects into the harness to see if it is just wiring, but what should I do about codes 63 and 66? Should I somehow connect a wire to the ABS unit and ground it?


Also, How do I clear codes?
 

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94 4x4,01 Blazer
2001 Blazer 4dr 4wd LT
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1,627 Posts
search on here for ABS cold solder joints- sounds like your ABS computer needs some TLC- and you might need that sensor too.
 

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Been there Done it
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ABS codes will come right back. It's a safety issue. At least from the manufacturers point of view. Common problem on the early units was a bad ground on the EHCU. IIRC they ground to the frame around the PS pump area. Or was it the front rad support?
Your biggest problem is the 4 wheel sensor system. Hard to find replacement parts for any of it. Again IIRC, GM went to the 3 sensor system when they went to the 4L60E in 93 by using the VSS for the rear input and eliminating the 4th brake wiring and fluid lines. All later trucks pump both rear brakes simultaneously. Works fine since they aren't doing the much of the braking and you aren't steering them.
 

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Discussion Starter · #5 ·
ABS codes will come right back. It's a safety issue. At least from the manufacturers point of view. Common problem on the early units was a bad ground on the EHCU. IIRC they ground to the frame around the PS pump area. Or was it the front rad support?
Your biggest problem is the 4 wheel sensor system. Hard to find replacement parts for any of it. Again IIRC, GM went to the 3 sensor system when they went to the 4L60E in 93 by using the VSS for the rear input and eliminating the 4th brake wiring and fluid lines. All later trucks pump both
I have a junkyard nearby that may have the correct computer in good condition. Do you think I could rig up a ground wire for the EHCU and ground it that way?
I have attached some pictures of codes from the Haynes Repair Manual. I’m going to check the speed sensor and clean the 8 pin connector and check for looseness. Before I do anything else.
Font Line Parallel Paper Document
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Font Screenshot Rectangle Parallel Number
Font Material property Screenshot Rectangle Parallel
 

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Discussion Starter · #6 ·
Well…I went and cleared the codes once I found out how to, and the only code that immediately came back was 31, for an intermittent problem on the right rear wheel speed sensor. I took it for a drive and code 32 showed up. It says there is no signal from the right rear WSS and to take the wheel off and check. Anyways, my EHCU may be in “perfect” condition…
I followed the wiring back to the speed sensor connector and did an ohm test. There is no closed circuit in this sensor. I’m gonna go replace it and clear codes again, and yes, I’ll use a feeler gauge to check the clearance between the sensor and the ring.
 
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