Navigating the intricacies of your 1995 Chevrolet Suburban’s Anti-lock Braking System (ABS) can be challenging, especially when faced with the older OBD1 diagnostic system. While the desire to upgrade to the more modern OBD2 ABS might cross your mind, understanding and troubleshooting your existing OBD1 system is crucial. This guide provides a straightforward approach to reading your 1995 Suburban’s OBD1 ABS fault codes, empowering you to diagnose potential issues effectively.
Understanding OBD1 ABS on Your 1995 Suburban
The 1995 Suburban, like many vehicles of its era, utilizes an OBD1 (On-Board Diagnostics, first generation) system. Unlike the standardized OBD2 system that became commonplace later, OBD1 systems are manufacturer-specific and often require unique procedures to access diagnostic information. For your Suburban’s ABS, retrieving fault codes involves a manual process, but it’s readily achievable with a few simple steps.
Locating the ALDL Connector
The key to accessing your OBD1 ABS codes lies in the Assembly Line Diagnostic Link (ALDL) connector. This connector is typically located under the dashboard, often on the driver’s side. It’s a multi-pin connector, and for our purpose of reading ABS codes, we’ll be focusing on specific pins.
Reading OBD1 ABS Codes – Grounding Pin H
To initiate the diagnostic sequence and retrieve the ABS codes, you’ll need to ground pin H of the ALDL connector. Pin A is a ground pin, making it convenient to use as your grounding point. Here’s how to proceed:
- Locate Pins A and H on the ALDL connector. Refer to your Suburban’s service manual or online diagrams if needed to correctly identify these pins.
- Use a jumper wire to connect Pin A to Pin H. A simple piece of wire will suffice to create this temporary connection.
- Turn the ignition ON, but do not start the engine. This powers up the vehicle’s electrical system and the ABS control module.
- Observe the Anti-lock lamp on your dashboard. The lamp will initially illuminate for approximately four seconds.
- Count the blinks. After the initial four seconds, the Anti-lock lamp will begin to blink a series of codes. It will start with a “1-2” code, which is a system check and indicates proper operation of the diagnostic system, not a fault. Following the “1-2” code, any stored trouble codes will be blinked out as two-digit codes. For example, code 21 would be blinked as two blinks, then a short pause, then one blink.
Alt text: Diagram showing OBD1 ALDL connector with pins labeled, including pin A (ground) and pin H (ABS diagnostic pin).
Interpreting the Codes
Carefully record the blinked codes. Each code corresponds to a specific area or component within the ABS system. The following is a list of OBD1.5 ABS codes relevant to your 1995 Suburban:
OBD1.5 ABS Trouble Codes:
- CODE 21 – FRONT RIGHT SENSOR CIRCUIT OPEN/SHORTED
- CODE 22 – INTERMITTENT SIGNAL, FRONT RIGHT SENSOR
- CODE 23 – MISSING SIGNAL, FRONT RIGHT SENSOR
- CODE 25 – FRONT LEFT SENSOR CIRCUIT OPEN/SHORTED
- CODE 26 – INTERMITTENT SIGNAL, FRONT LEFT SENSOR
- CODE 27 – MISSING SIGNAL, FRONT LEFT SENSOR
- CODE 31 – REAR RIGHT SENSOR CIRCUIT OPEN/SHORTED
- CODE 32 – INTERMITTENT SIGNAL, RIGHT REAR SENSOR
- CODE 33 – MISSING SIGNAL, REAR RIGHT SENSOR
- CODE 35 – REAR LEFT SENSOR CIRCUIT OPEN/SHORTED
- CODE 36 – INTERMITTENT SIGNAL, REAR LEFT SENSOR
- CODE 37 – MISSING SIGNAL, REAR LEFT SENSOR
- CODE 41 – ELECTRICAL DISTURBANCE INLET VALVE (CIRCUIT – FRONT RIGHT)
- CODE 42 – ELECTRICAL DISTURBANCE OUTLET VALVE (CIRCUIT – FRONT RIGHT)
- CODE 44 – ELECTRICAL DISTURBANCE ISOLATION VALVE SV1 (CIRCUIT – FRONT LEFT) NOTE: TCS ONLY
- CODE 45 – ELECTRICAL DISTURBANCE INLET VALVE (CIRCUIT – FRONT LEFT)
- CODE 46 – ELECTRICAL DISTURBANCE OUTLET VALVE (CIRCUIT – FRONT LEFT)
- CODE 48 – ELECTRICAL DISTURBANCE ISOLATION VALVE SV2 (CIRCUIT -FRONT RIGHT) NOTE: TCS ONLY
- CODE 51 – ELECTRICAL DISTURBANCE INLET VALVE (CIRCUIT – REAR RIGHT)
- CODE 52 – ELECTRICAL DISTURBANCE OUTLET VALVE (CIRCUIT – REAR RIGHT)
- CODE 55 – ELECTRICAL DISTURBANCE INLET VALVE (CIRCUIT – REAR LEFT)
- CODE 56 – ELECTRICAL DISTURBANCE OUTLET VALVE (CIRCUIT – REAR LEFT)
- CODE 61 – PUMP MOTOR RUN FAULT
- CODE 62 – PUMP PRESSURE FAULT DURING ABS STOP
- CODE 71 – CHECKSUM ERROR
- CODE 72 – TRAVEL SWITCH INPUT NOT PROCESSABLE
- CODE 73 – FLUID LEVEL SWITCH INPUT NOT PROCESSABLE
- CODE 74 – PRESSURE SWITCH CIRCUIT NOTE: TCS ONLY
- CODE 75 – PCM REQUESTED TCS DISABLE NOTE: TCS ONLY
- CODE 76 – UART SDL CIRCUIT/SIGNAL
- CODE 77 – DELIVERED TORQUE PWM CIRCUIT/SIGNAL NOTE: TCS ONLY
This list covers a range of potential issues, from sensor malfunctions to valve and pump problems. Once you have your codes, you can begin to pinpoint the source of the ABS problem.
Clearing OBD1 ABS Codes
After addressing the fault indicated by the codes, you’ll want to clear the codes from the ABS system’s memory. OBD1 ABS codes will automatically clear after 100 ignition cycles if the fault is no longer present. However, you can manually clear most codes using the following procedure:
- With the ignition OFF, jump Pin H to Pin A again.
- Turn the Ignition ON.
- Wait approximately 4 seconds for the Anti-lock lamp to go out.
- Disconnect the ground link (remove jumper wire).
- Wait about 1 second.
- Re-establish the ground link (reconnect jumper wire).
- Wait 1 second.
- Remove the link again.
- Repeat steps 4-8 three times slowly within 10 seconds.
This sequence should clear most stored ABS codes.
Thinking About OBD2 Conversion?
While reading OBD1 codes is manageable, the appeal of converting to an OBD2 ABS system for your 1995 Suburban is understandable. OBD2 offers enhanced diagnostics and greater compatibility with modern scan tools. However, converting from OBD1 to OBD2 ABS is not a straightforward plug-and-play process. It typically involves significant modifications, including replacing the ABS control module, sensors, and potentially wiring harnesses.
Alt text: Image comparing OBD1 and OBD2 connectors side-by-side, highlighting the differences in pin configurations and system complexity.
Important Note: If you find yourself unable to extract codes using the method described, or if you are considering an OBD2 conversion, it is highly recommended to consult with a qualified automotive technician. Diagnosing ABS issues and undertaking system modifications require expertise to ensure safety and proper functionality.
Understanding your 1995 Suburban’s OBD1 ABS system is the first step in maintaining its braking performance. By following these steps, you can effectively read and clear ABS codes, and make informed decisions about any potential upgrades or repairs.
