As a classic truck enthusiast and owner, understanding your 1990 Chevy Silverado’s onboard diagnostics is crucial for maintenance and repair. While modern vehicles use OBD2 systems, your 1990 Silverado utilizes an earlier OBD-I system. This guide will walk you through how to check trouble codes on your 90 Chevy Silverado using its OBD-I system, ensuring you can diagnose issues effectively.
The 1990 Chevy Silverado, like other models from 1988 to 1995, uses an OBD-I system. Unlike the standardized OBD2 system that became common later, OBD-I is manufacturer-specific and often simpler. Accessing the diagnostic information on your Silverado requires a simple procedure and no specialized tools. You’ll only need a paper clip or a small wire to retrieve the diagnostic codes.
Here’s how to check the trouble codes on your 1990 Chevy Silverado OBD-I system:
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Locate the DLC Connector: The Diagnostic Link Connector (DLC), also known as the Assembly Line Diagnostic Link (ALDL), is typically located under the driver’s side dashboard.
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Prepare to Jumper Terminals A and B: With the ignition switch turned off, use your paper clip or wire to bridge the A and B terminals on the DLC connector. These terminals are usually located at the top right of the connector.
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Turn Ignition On: Turn the ignition switch to the “ON” position, but do not start the engine. Observe the “Service Engine Soon” light on your dashboard.
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Reading the Trouble Codes: The “Service Engine Soon” light will begin to flash, indicating trouble codes. Code 12 is the system’s starting point and is normal. It’s represented by a flash, pause, flash flash. Each code will be displayed three times before moving to the next code in numerical order. The sequence repeats once all codes have been displayed, starting again with code 12.
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Understanding Code 12: Code 12 simply indicates that the diagnostic system is functioning and is not a fault indicator.
It’s important to remember that a trouble code is merely a starting point for diagnosis. It signals a potential area of concern but doesn’t definitively mean a specific sensor or component is faulty. For example, a code might indicate an oxygen sensor issue, but the real problem could be a vacuum leak or another related system affecting the sensor’s readings.
Common OBD-I Trouble Codes for 90 Chevy Silverado Gasoline Engines:
Here’s a list of common OBD-I codes you might encounter on your 1990 Chevy Silverado with a gasoline engine:
- 13 – O2 Sensor Circuit Open
- 14 – ECT/CTS Sensor Circuit Low (High Temperature)
- 15 – ECT/CTS Sensor Circuit High (Low Temperature)
- 16 – VSS Buffer Fault
- 21 – TPS Circuit High (Signal Voltage High)
- 22 – TPS Circuit Low (Signal Voltage Low)
- 24 – VSS Circuit Low
- 28 – TR Pressure Switch Assembly
- 32 – EGR Valve Error
- 33 – MAP Sensor Circuit High (Low Vacuum)
- 34 – MAP Sensor Circuit Low (High Vacuum)
- 35 – IAC Error
- 36 – Idle Speed Control Actuator Error (if equipped)
- 42 – IC Error
- 43 – KS Error
- 44 – Lean Exhaust
- 45 – Rich Exhaust
- 51 – PROM Error
- 53 – System Voltage High
- 54 – Fuel Pump Relay Circuit Low Voltage
- 55 – ECM/PCM Error
To clear codes after addressing the issue, you can disconnect the battery for about 20 seconds. Codes will also automatically clear after 50 engine starts if the problem does not reoccur.
Understanding and utilizing the OBD-I system in your 1990 Chevy Silverado is a valuable skill for any owner. By following these steps and understanding the common codes, you can take a proactive approach to vehicle maintenance and ensure your classic Chevy truck stays running smoothly. Remember to consult a repair manual or a professional mechanic for in-depth troubleshooting and repairs based on the codes you retrieve.
