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Username Post: 1991chevy truck flashing brake light on dash        (Topic#235446)
Forum Newbie
Posts: 2

Reg: 02-11-10
02-11-10 01:02 PM - Post#1860771    

I've got a '91 chevy truck, 4x4, 350 automatic. The brake light on the dash is flashing 1 - 3 anybody have an idea? It's not the check engine light.


Subject Matter Expert - Senior Member
Posts: 3923
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
02-11-10 04:56 PM - Post#1860915    
    In response to ghunkele

It sounds like an RWAL code 4

Code 4 = Grounded or closed RABS or RWAL valve switch.

RWAL stands for REAR WHEEL ANTILOCK. RWAL was standard equipment starting in 1988 on full size trucks.

1988 and newer trucks of that body style that do not have 4 wheel ABS have RWAL.

The RWAL system can store trouble codes, but it is only capable of storing one code at a time.

If the light is blinking the manual states you should still check the codes by turning the key on (engine not running) and put a jumper wire between terminal A and H of the ALDL. Count the brake light flashes.

You can retrieve RWAL codes without a scan tool.

If the instrument panel light is on, to retrieve RWAL codes connect a jumper wire between terminal H and terminal A of the ALDL connector with the key on (engine not running). Watch the dash brake lamp and count the blinks. Sometimes RWAL system send out a phantom blink before the code blinks start. It can take up to 20 seconds for the code to start coming out.

GM RWAL code 4 testing:
NOTE: the Isolation/Dump valve is out by the master cylinder. It is an aluminum block with two round things and has brake lines going to it.
Key OFF, unplug the Isolation/Dump valve, test the resistance between terminal C of the Isolation/Dump valve and the body of the valve. This tests the switch. Also test the resistance between terminal C and terminal D of the Isolation/Dump Valve. Both tests should measure greater then 50,000 ohms. If they measure less than this the Isolation/ Dump valve is bad.

If it tests ok, with the connecter still unplugged, turn the key on, measure the voltage between terminal C and terminal D of the wire harness that connects to the Isolation/Dump valve. It should be 4 volts or more. If it reads 0 volts replace the RWAL ECU (flat black plastic box by the master cylinder). If it tested 4 volts or more, and it sets a code 4 again, after clearing the code, replace the Isolation/Dump valve.

Clearing codes
You can clear the code by removing the power to the RWAL module for 10 seconds. Multiple circuits send power to the RWAL module and the fuses may be labeled STOP/hazard and BRAKE. Removing a fuse labeled RWAL may not clear the code. GM information on which fuse/fuses to pull is not very reliable.

I see it’s your first post. Welcome to the message board.

You can do a search here in 88-98 full size truck forum on RWAL and my username and you should be able to find many threads on RWAL.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.

Forum Newbie
Posts: 2

Reg: 02-11-10
02-12-10 04:47 AM - Post#1861167    
    In response to Chevytech

thanks, I'll check it out

spastik monkey 
Forum Newbie
Posts: 9

Reg: 04-14-13
04-14-13 12:59 PM - Post#2335593    
    In response to ghunkele

What happens when you jumper the terminals and the brake light doesn't flash?

Frequent Contributor
Posts: 1921

Loc: Los Angeles
Reg: 08-07-07
04-14-13 10:38 PM - Post#2335751    
    In response to spastik monkey

What happens when you ask this in the Trucks section?

Jim B.


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