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ABS Brakes

Troubleshooting The '86-'91 ABS Brake System

Andy Bolig May 1, 2001

Step By Step

This is the main part we’ll be focusing on. Other than the fuses, most of the trouble areas will be found here. The control module and hydraulic modulator are located in a small compartment behind the driver seat.

If you get the dreaded ABS light, first check the fuses. There will be a 10-amp brake fuse and a 10-amp fuse for the gauges. If they’re OK, proceed to the modulator assembly. Since our car was a convertible, we had to remove the speaker assembly to get to the module.

The most common problem with the ABS system is this relay (PN 1636973). There are several tests you can do to check whether it’s working properly. The pins have numbers to identify them, and we’ll be referring to these numbers and the corresponding wire colors to do the troubleshooting.

To check this relay, turn on the key and use a test light to make sure there is voltage at pin numbers 15 (pink/black wire), 30 (orange/black wire), and 87 (orange wire). If there is voltage at each of these connections, the relay is working properly.

If the relay has no voltage, check the connector that leads to the relay to make sure it has a good connection.

Also check the ground on this relay by testing pin number 31 (black wire) for voltage. This is the ground for the relay, so there should be no voltage. If the test light illuminates, you have a bad ground on this wire. Check the ground connection further down the wire (shown) to see if it has proper contact. If the test light illuminates on both sides of the connector, your ground problem is further down the line.

If the module relay checks out, this relay will be the next to check. There are two of them. One operates the pump motor, and the other operates the solenoid. Both relays are located on top of the pump. Because they connect directly to the top of the pump, check these relays by simply exchanging each with a new relay.

Or you could remove the control module connector and check pin position 9 for voltage after the relay.

If you run all of these tests and still haven’t found the problem, check the high-amperage circuit to see if it has power.

ABS brakes are a complex but valuable asset to the Corvette driver. As with many complex systems, they require some attention from time to time. The system is designed to give the driver notice that it's working properly. A whirring sound accompanied by a pulsation of the brake pedal are typical signs that the system is working as it should. If these events aren't noticed, there's a systematic solution to troubleshooting the ABS that can be done in the driveway by the most novice of mechanics. Follow along as we diagnose ABS.

If you have an intermittent problem with your ABS, check your module relay by tapping it to see if it's sticking. As complex as this system is, Chris Petris reports that he has had to replace only one module in all his years of working on Corvettes. He says the reason for the failure is the car was repeatedly jump-started, and he believes the cables may have been crossed at some time. With that in mind, these tests should identify any problem you'd typically find with your ABS brakes.

Considering that the purchase price of a test light and the necessary relays is cheaper than the cost of a technician to find the problem, it makes perfect sense to arm yourself with this information and strengthen your wallet, as well as your ABS.


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