GM Astro/Safari 1985-1996 Repair Guide

General Information

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See Figures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 and 14





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Fig. Fig. 1: RWAL brake system diagram

 


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Fig. Fig. 2: RWAL wiring diagram

 


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Fig. Fig. 3: RWAL connector pinouts

 


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Fig. Fig. 4: 4WAL hydraulic system-1996 shown

 


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Fig. Fig. 5: 4WAL Component locations-except 1996 models

 


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Fig. Fig. 6: 4WAL Component locations-1996 models

 


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Fig. Fig. 7: Three sensor 4WAL brake system diagram-Except 1996 models

 


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Fig. Fig. 8: Four sensor 4WAL brake system diagram-Except 1996 models

 


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Fig. Fig. 9: Three sensor 4WAL brake system wiring diagram-Except 1996 models

 


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Fig. Fig. 10: Four sensor 4WAL brake system wiring diagram-Except 1996 models

 


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Fig. Fig. 11: 4WAL connector pinouts-Except 1996 models

 


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Fig. Fig. 12: 4WAL brake system diagram-1996 models

 


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Fig. Fig. 13: 4WAL brake system wiring diagram-1996 models

 


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Fig. Fig. 14: 4WAL brake system connector pinouts-1996 models

 

There are two basic types of anti-lock systems available for this vehicle; a Rear Wheel Anti-Lock (RWAL) brake system and 4 Wheel Anti-Lock (4WAL) brake system. The 4WAL system has two variations; a 3 sensor system and a 4 sensor system. The 2WD vehicles will be equipped with the 3 sensor system, but the AWD vehicles can be equipped with either. The systems are easily identified by looking at the rear wheels for a sensor harness. If there is a sensor harness and thus, rear wheel sensors, it is the 4 sensor system. If the vehicle is not equipped with a harness, it is the 3 sensor system. The 4 sensor system takes it speed references from each of the wheels. The 3 sensor system takes its speed references from each of the front wheels and the vehicle speed sensor located in the transmission (2WD) or the transfer case (AWD).

The RWAL system components consist of the Vehicle Speed Sensor (VSS), the Electronic Control Unit (ECU), the isolation/dump valve and the Vehicle Speed Sensor Buffer (also known as the Digital Ratio Adapter). The ECU also receives signals from various brake switches.

The 4WAL system components consist of the Electro-Hydraulic Control Unit (ECHU) valve (also known as the Brake Pressure Modulator Valve or BPMV), the wheel speed sensors, Vehicle Speed Sensor (VSS) on 3 sensor systems and the VSS Buffer.

 
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