How to Check Engine Light 2nd Gen 4runner

Discover how to diagnose and reset the check engine light on your 2nd generation Toyota 4Runner. This guide walks you through manual code reading, using OBD1 scanners, and understanding common issues—no mechanic required.

Key Takeaways

• Manual Code Reading: You can read diagnostic trouble codes (DTCs) without a scanner by using the 4Runner’s built-in ECU blink method.
• OBD1 System: The 2nd gen 4Runner uses OBD1, which requires specific tools or jumper wires—not modern OBD2 scanners.
• Common Causes: Frequent triggers include faulty oxygen sensors, loose gas caps, vacuum leaks, and ignition coil issues.
• Resetting the Light: After repairs, you can reset the light by disconnecting the battery or using a compatible OBD1 scanner.
• Preventive Maintenance: Regular tune-ups and using quality fuel help prevent false or recurring engine light alerts.
• DIY-Friendly: Most 2nd gen 4Runner owners can perform basic diagnostics at home with minimal tools.
• 2026 Relevance: Even in 2026, these older models remain reliable—and knowing how to handle the check engine light saves time and money.

How to Check Engine Light on a 2nd Gen 4Runner: A Complete 2026 Guide

If you own a second-generation Toyota 4Runner—produced from 1990 to 1995—you’re driving a rugged, dependable SUV that’s stood the test of time. Even in 2026, these vehicles remain popular among off-roaders, collectors, and daily drivers who value simplicity and durability. But like any older vehicle, they can develop issues, and one of the most common signs something might be off is the dreaded check engine light.

Unlike modern cars with advanced onboard diagnostics, the 2nd gen 4Runner uses an older system called OBD1 (On-Board Diagnostics, version 1). This means you can’t just plug in a standard OBD2 scanner and get instant results. But don’t worry—you don’t need to rush to a mechanic every time that little orange light flickers on. With a few simple tools and a bit of know-how, you can read the diagnostic trouble codes (DTCs), understand what they mean, and even reset the light yourself.

In this guide, we’ll walk you through everything you need to know about checking and diagnosing the check engine light on your 2nd gen 4Runner. Whether you’re a seasoned DIYer or a first-time 4Runner owner, this step-by-step tutorial will empower you to take control of your vehicle’s health—saving you time, money, and unnecessary stress.

By the end of this guide, you’ll be able to:

• Locate the diagnostic port in your 4Runner
• Read trouble codes manually using the ECU blink method
• Use an OBD1 scanner if you have one
• Interpret common codes and their meanings
• Troubleshoot and fix typical issues
• Reset the check engine light safely

Let’s get started.

Understanding the 2nd Gen 4Runner’s Check Engine Light System

Before diving into the how-to steps, it’s important to understand how the check engine light works in your 2nd gen 4Runner. Unlike newer vehicles with OBD2 systems that provide standardized, universal codes, the 2nd gen 4Runner uses Toyota’s proprietary OBD1 system. This system was designed in the late 1980s and early 1990s, so it’s less sophisticated but still effective for diagnosing basic engine and emissions issues.

When the check engine light comes on, it means the vehicle’s Engine Control Unit (ECU) has detected a problem with one or more of the engine’s systems. The ECU stores a diagnostic trouble code (DTC) that corresponds to the specific issue. These codes can range from minor (like a loose gas cap) to more serious (like a failing oxygen sensor or ignition coil).

The good news? You don’t need expensive equipment to read these codes. Toyota built a simple, manual method into the 4Runner that allows you to retrieve the codes using just a paperclip or jumper wire and your eyes. This method involves shorting two terminals in the diagnostic port, which triggers the ECU to flash the check engine light in a specific pattern. Each flash sequence corresponds to a number, and by counting the flashes, you can determine the code.

In 2026, while OBD2 scanners dominate the market, OBD1 tools are still available—though less common. If you plan to work on older Toyotas regularly, investing in an OBD1 scanner compatible with Toyota vehicles (like the Actron CP9145 or a generic OBD1-to-OBD2 adapter) can make diagnostics faster and more accurate. But for most owners, the manual method is sufficient and cost-effective.

Tools You’ll Need

Before you begin, gather the following tools. Most are inexpensive and easy to find:

• Paperclip or jumper wire: A standard metal paperclip or a short piece of 14–16 gauge wire with stripped ends. This is used to short the diagnostic terminals.
• Screwdriver (Phillips or flathead): To access the diagnostic port if it’s covered.
• Flashlight: To see the diagnostic port clearly, especially in low light.
• Notepad and pen: To record the trouble codes as you read them.
• OBD1 scanner (optional): If you have one, it can simplify the process and provide more detailed information.
• Multimeter (optional): Useful for testing sensors and electrical connections during troubleshooting.

Most of these items are likely already in your garage or toolbox. The paperclip method is especially handy because it requires no power source or special equipment—just a bit of patience.

Step 1: Locate the Diagnostic Port

The first step in checking the check engine light is finding the diagnostic port. In the 2nd gen 4Runner, this port is located under the hood, near the driver’s side firewall. It’s a small, rectangular connector with multiple pins—typically 12 or 16, depending on the model year and engine type.

To find it:

1. Open the hood and look along the firewall (the metal wall separating the engine bay from the cabin).
2. On the driver’s side, near the brake booster or master cylinder, you’ll see a small black or gray plastic connector.
3. It’s usually labeled “DIAGNOSTIC” or “DLC” (Data Link Connector), though the label may be faded.

If you can’t find it, consult your owner’s manual or look for a small cover that can be pried off with a screwdriver. Some models have the port tucked behind a rubber grommet or plastic shield.

Once located, clean the area gently with a dry cloth to remove dust or debris. This ensures a good connection when you insert the jumper wire.

Step 2: Prepare the Vehicle for Diagnostics

Before reading the codes, make sure your 4Runner is in the correct state:

• Turn off the engine: The vehicle should be off, but the key should be in the “ON” position (ignition on, engine off). This powers the ECU without starting the engine.
• Ensure all accessories are off: Turn off the radio, lights, A/C, and any other electrical systems to avoid interference.
• Check the battery: A weak battery can cause false codes or prevent the ECU from responding. If your battery is old or showing signs of weakness, charge or replace it before proceeding.

This setup mimics the conditions under which the ECU normally operates during a diagnostic cycle.

Step 3: Short the Diagnostic Terminals

Now it’s time to trigger the ECU to display the trouble codes. This is done by shorting two specific pins in the diagnostic port.

Identify the Correct Pins

In most 2nd gen 4Runners, you’ll need to short the TE1 and E1 terminals. These are typically located in the top row of the diagnostic connector:

• TE1: Test Engine 1 – used to initiate diagnostic mode.
• E1: Ground – provides a reference point for the signal.

The exact pin layout can vary slightly by model year and engine (2.4L 22RE or 3.0L 3VZE), so it’s a good idea to double-check a wiring diagram if you’re unsure. However, in most cases, TE1 is the second pin from the left on the top row, and E1 is the second pin from the right on the bottom row.

Insert the Jumper Wire

Take your paperclip or jumper wire and straighten it out. Carefully insert one end into the TE1 pin and the other into the E1 pin. Make sure the metal ends are fully seated and not touching any other pins.

Important: Do not force the wire. The pins are small, and bending them can damage the connector. If resistance is felt, double-check the pin positions.

Once the wire is in place, the ECU will enter diagnostic mode. You’ll know it’s working when the check engine light begins to flash.

Step 4: Read the Trouble Codes

With the jumper wire connected and the key in the “ON” position, watch the check engine light on your dashboard. It will begin to flash in a specific pattern that corresponds to the stored trouble codes.

Understanding the Flash Pattern

The flashes follow a simple numeric code system:

• A long flash (about 1.5 seconds) represents a “10.”
• A short flash (about 0.5 seconds) represents a “1.”
• There is a pause between digits and a longer pause between codes.

For example:

• Two long flashes followed by three short flashes = Code 23
• One long flash, pause, four short flashes = Code 14

Write down each code as it appears. The ECU will cycle through all stored codes, then repeat the sequence. Once you’ve recorded all codes, you can remove the jumper wire.

Common 2nd Gen 4Runner Trouble Codes

Here are some of the most frequently encountered codes and what they mean:

• Code 12: No RPM signal – often caused by a faulty crankshaft position sensor or wiring issue.
• Code 14: Ignition signal – typically points to a bad ignition coil or distributor.
• Code 21: Oxygen sensor (Bank 1) – indicates a faulty O2 sensor or exhaust leak.
• Code 22: Coolant temperature sensor – sensor may be out of range or disconnected.
• Code 25: Air/fuel ratio too rich – could be a clogged fuel injector or faulty MAF sensor.
• Code 31: Air pump system – common on models with smog pumps; often a stuck valve or clogged hose.
• Code 41: Throttle position sensor – sensor may be misadjusted or failing.
• Code 43: Starter signal – ECU not receiving signal from starter; check ignition switch or wiring.

Note that some codes may appear even if the issue has been resolved. The ECU stores “pending” codes until they are cleared or confirmed.

Step 5: Troubleshoot and Fix the Issue

Once you’ve identified the trouble code, it’s time to diagnose and fix the problem. Here’s how to approach common issues:

Code 12 – No RPM Signal

This code often appears when the ECU doesn’t detect engine rotation. Check the crankshaft position sensor (located near the harmonic balancer) for damage or loose wiring. Clean the sensor and connector, and ensure the gap between the sensor and reluctor wheel is correct (usually 0.5–1.5mm).

Code 14 – Ignition Signal

A bad ignition coil or distributor can cause this code. Test the coil’s primary and secondary resistance with a multimeter. If out of spec, replace it. Also, inspect the distributor cap and rotor for wear or carbon tracking.

Code 21 – Oxygen Sensor

The O2 sensor monitors exhaust gases and helps the ECU adjust the air/fuel mixture. A faulty sensor can reduce fuel economy and increase emissions. Replace the sensor if it’s old or showing erratic readings. Use a Toyota-specific sensor for best results.

Code 22 – Coolant Temperature Sensor

This sensor tells the ECU how hot the engine is. If it’s faulty, the engine may run rich or lean. Test the sensor’s resistance at different temperatures and compare it to the factory specs. Replace if necessary.

Code 41 – Throttle Position Sensor

The TPS tells the ECU how far the throttle is open. If it’s misadjusted or failing, you may experience poor acceleration or stalling. Adjust the sensor according to the service manual, or replace it if damaged.

Code 43 – Starter Signal

This code appears when the ECU doesn’t receive a signal from the starter during cranking. Check the ignition switch, starter relay, and wiring harness for continuity and proper voltage.

Step 6: Reset the Check Engine Light

After repairing the issue, you’ll want to clear the trouble codes and turn off the check engine light. There are two main methods:

Method 1: Disconnect the Battery

• Turn off the ignition and remove the key.
• Disconnect the negative terminal of the battery using a wrench.
• Wait at least 10–15 minutes to ensure the ECU fully resets.
• Reconnect the battery and start the engine.

This method clears the ECU’s memory, including stored codes. However, it also resets radio presets, clock, and other settings.

Method 2: Use an OBD1 Scanner

If you have an OBD1 scanner, you can clear the codes electronically without disconnecting the battery. Simply connect the scanner, select “Clear Codes,” and follow the prompts.

Method 3: Drive Cycle Reset (Sometimes Works)

In some cases, the ECU will clear the code automatically after a certain number of error-free drive cycles (typically 40–80 warm-up cycles). However, this is unreliable and not recommended as a primary method.

Preventive Maintenance Tips

To reduce the chances of the check engine light coming on in the future, follow these maintenance tips:

• Use quality fuel: Stick to top-tier gasoline to prevent carbon buildup and sensor contamination.
• Replace spark plugs and wires regularly: Follow the 30,000–60,000 mile interval depending on driving conditions.
• Check the gas cap: A loose or damaged cap can trigger a vapor leak code (though not always stored in OBD1).
• Inspect vacuum hoses: Cracked or disconnected hoses can cause lean codes and poor performance.
• Clean the MAF sensor: Use MAF cleaner spray to remove dirt and oil buildup.
• Monitor engine temperature: Overheating can damage sensors and trigger false codes.

Regular maintenance not only prevents check engine light issues but also extends the life of your 4Runner.

Troubleshooting Common Problems

Even with proper diagnostics, you may encounter issues. Here are some common problems and solutions:

The Check Engine Light Doesn’t Flash

• Ensure the key is in the “ON” position (engine off).
• Double-check the jumper wire connection—TE1 and E1 must be properly shorted.
• Test the battery voltage—low voltage can prevent the ECU from responding.
• Inspect the diagnostic port for corrosion or damage.

Codes Keep Coming Back

• The issue may not be fully resolved. Recheck your repair.
• Intermittent faults (like loose wiring) may require further inspection.
• Some sensors degrade over time and may need replacement even if they test okay.

Multiple Codes Appear

• Start with the lowest number code—it’s often the root cause.
• Some codes are secondary effects (e.g., a bad O2 sensor can trigger a fuel trim code).
• Address one issue at a time and retest.

Conclusion

Checking the check engine light on a 2nd gen 4Runner doesn’t have to be intimidating. With the right knowledge and a few simple tools, you can diagnose issues, understand what’s going on under the hood, and take action—all without visiting a mechanic. Whether you use the manual blink method or an OBD1 scanner, the process is straightforward and empowering.

Even in 2026, these classic SUVs continue to deliver reliable performance, and knowing how to handle the check engine light ensures you get the most out of your 4Runner. Regular maintenance, prompt repairs, and a little DIY spirit will keep your ride running strong for years to come.

So the next time that little orange light flickers on, don’t panic. Grab a paperclip, follow this guide, and take control of your vehicle’s health. Your 2nd gen 4Runner deserves it.