1990 Chevrolet G20 Has A Check Engine Light

Troubleshooting the Check Engine Light in Your 1990 Chevrolet G20: Common Causes and Solutions

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Reviewed by
Devin Cabugcal
Written by RepairPal Car Genius
Updated January 14, 2025
0%
40% chance it's the
Emissions System
0%
60% chance it's
Something else
The most common reasons a 1990 Chevrolet G20 has a check engine light are an emissions system component, a sensor, or a catalytic converter.
  • Emissions System: A faulty emissions system component, such as an oxygen sensor or EGR valve, can lead to increased emissions and trigger the check engine light.
Proper diagnosis will determine the exact cause of your symptom, saving you money on unnecessary repairs. The diagnostic experts at RepairPal Certified shops have the right tools and experience to solve any symptom.

How much does it cost to fix a 1990 Chevrolet G20 has a check engine light?

Common Repairs

The total repair cost will vary based on the condition of your vehicle and the number of repairs needed to fix your symptom. Proper diagnosis will save you money by finding the exact repairs needed to fix your car right the first time.

A faulty oxygen sensor is one of the most common causes of a check engine light. Symptoms may include a decrease in fuel mileage, hesitation or misfiring from the engine, rough idling or even stalling. A faulty sensor may cause the vehicle to fail an emissions test.

Any time there is an emissions fault the check engine light will be displayed. The purpose of the check engine light is to inform the driver that an emission related fault has been found, and that there are on-board diagnostic (OBD) trouble codes stored in the powertrain or engine control module. Additionally, since the emissions systems are so intertwined into engine control and transmission control systems, symptoms may include nearly any sort of drivability concerns. This may include harsh shifting, failure to shift, hesitation on acceleration, jerking, engine failure to start or run, loss of power, or any number of other drivability issues.

Due to the nature of electrical systems on modern vehicles, the range of problems these can cause are nearly limitless. However, there is a way to categorize them in two ways. Permanent and intermittent problems. Permanent problems appear and remain. This may be the vehicle will not start, the radio does not work, or the door chime will not turn off among many, many others. These problems are more straight-forward to diagnose since they present themselves at all time. This means there will always be a fault to find. Intermittent electrical problems, however, can be difficult or impossible to locate, since they appear then disappear without warning. The best case scenario for an intermittent issue is when replicating the problem is easily accomplished and understood. This allows a technician to make an issue semi-permanent, allowing them to find the fault. Other issues that come and go without warning and cannot be replicated on demand must occur when the technician is servicing the vehicle, otherwise there is no problem to correct. It is most important to understand that electrical system faults always require inspection, and can include the vehicle working in any manner, or not working at all.

Like we noted in the last section, general diagnosis symptoms are the most vague of the bunch. There are several diagnostic spectrums, electrical diagnosis, drivability diagnostics, engine diagnostics, transmission diagnostics, and the list could continue for about 5 or 10 more spectrums of diagnostics. The most important take-away here, is that general diagnostics are diagnostics that have no other spectrum in which they fit, or the problem is unknown. This means that any vehicle left outside of a repair facility with the keys and an authorization to perform diagnosis will be diagnosed under the general diagnosis spectrum.

When the Check Engine Light comes on, you may experience engine performance issues such as poor acceleration, rough idling, or an engine that won't start. In some cases, no abnormal symptoms will be experienced. Other systems like the transmission or ABS can cause the Check Engine Light to illuminate and lights for those systems can come on at the same time. Similar lights may say "Check Engine Soon", "Malfunction Indicator Light" or just "Check". In rare case the engine can overheat.

What are the initial diagnostic steps to take when a 1990 Chevrolet G20 has a check engine light?

When faced with a check engine light on your 1990 Chevrolet G20, it's essential to adopt a structured diagnostic approach to efficiently identify the underlying problem. Start with an initial inspection and diagnostic overview, which includes taking the vehicle for a test drive to assess its overall performance and conducting a basic tune-up to ensure all systems are functioning correctly. Next, check for trouble codes by grounding terminals A and B with the ignition in the "ON" position; this will allow you to retrieve any stored codes that can guide your troubleshooting efforts. Pay particular attention to common triggers related to emission issues, as these are frequent culprits for the check engine light activation. Additionally, turning the ignition switch on without starting the engine can help you observe the "Service Engine Soon" light, providing further insights into the specific issues detected by the onboard diagnostics system. By following these steps, you can effectively narrow down the potential causes of the check engine light and take informed actions towards resolving the issue.

What are the common problems that could cause the check engine light to illuminate in a 1990 Chevrolet G20?

When the check engine light comes on in a 1990 Chevrolet G20, it can be a source of frustration for DIYers looking to maintain their vehicle. One of the most frequent culprits is a faulty oxygen sensor, which plays a crucial role in monitoring exhaust gases and ensuring optimal fuel efficiency. Another common issue is a loose or damaged gas cap; this seemingly minor problem can lead to fuel vapor leaks, triggering the light. Additionally, problems with the catalytic converter, such as clogs or failures, can also cause the check engine light to illuminate, indicating a need for further inspection. Spark plug or ignition coil issues are other potential causes, as they can lead to misfires that affect engine performance. A malfunctioning mass airflow sensor can disrupt the air-fuel mixture, while an engine misfire, often stemming from bad spark plugs or fuel injectors, can also trigger the warning light. Lastly, dysfunction in the exhaust gas recirculation (EGR) valve can contribute to the problem. Addressing these issues promptly is essential to prevent further damage and maintain the vehicle's performance, making it advisable for DIYers to conduct thorough diagnostics or consult a mechanic if needed.

How urgent is it to address the check engine light on a 1990 Chevrolet G20?

Addressing the check engine light on a 1990 Chevrolet G20 is not just a matter of convenience; it is a critical step in maintaining the vehicle's overall health and safety. The check engine light serves as an early warning system, indicating that there may be underlying issues with the engine or emissions system. Ignoring this warning can lead to decreased performance and fuel efficiency, and in severe cases, it may result in significant engine damage that could require costly repairs. Moreover, neglecting the check engine light can compromise the safety and reliability of your vehicle, increasing the risk of breakdowns or accidents while driving. Therefore, it is essential to act promptly when the check engine light illuminates, as addressing the issue early can save you time, money, and ensure a safer driving experience.

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