1987 How to Read Check Engine Light Codes

Reading check engine light codes in 1987 vehicles is simpler than you think—no fancy tools required. This guide walks you through the manual method using your car’s diagnostic port and the flashing check engine light to decode issues fast.

Key Takeaways

• Understanding 1987 how to read check engine light codes: Provides essential knowledge

Understanding the 1987 Check Engine Light System

If you’re driving a 1987 vehicle and the check engine light suddenly comes on, don’t panic. Unlike today’s cars packed with advanced computers and Bluetooth scanners, 1987 models use a much simpler system called OBD-I—On-Board Diagnostics, Generation One. This early version of vehicle diagnostics was designed to monitor emissions and basic engine functions, and while it’s not as sophisticated as modern OBD-II systems, it’s surprisingly effective when you know how to use it.

The check engine light in your 1987 car isn’t just a warning—it’s a direct line to your vehicle’s internal diagnostics. When the engine control module (ECM) detects a problem, it stores a trouble code and triggers the light to alert you. The best part? You don’t need a $200 scanner or a trip to the mechanic to read these codes. With just a paperclip and a few minutes of your time, you can decode what your car is trying to tell you.

Back in 1987, automakers were still standardizing diagnostic systems. GM, Ford, and Chrysler each had their own approach, but they all shared a common goal: help drivers and technicians identify problems quickly. The check engine light was the universal signal, and the method of retrieving codes was designed to be accessible—even to the average car owner. This means you can take control of your vehicle’s health without relying on expensive tools or dealership visits.

Why the 1987 System Is Different

Unlike modern vehicles that use a universal OBD-II port and standardized codes, 1987 cars vary by manufacturer. GM vehicles, for example, often use a specific diagnostic connector under the dash, while Ford models might require a different grounding method. Chrysler vehicles from this era sometimes use a combination of key cycles and light flashes. This variation means you’ll need to know your car’s make and model to follow the correct procedure.

Despite these differences, the core principle remains the same: the ECM stores trouble codes and communicates them through the check engine light. When you initiate the diagnostic mode, the light will flash a sequence that corresponds to a specific code. For instance, two long flashes followed by three short flashes might mean code 23. Each digit is represented by the number of flashes—long flashes for tens, short for ones.

Another key difference is that 1987 systems don’t continuously monitor all components. They focus mainly on emissions-related parts like the oxygen sensor, exhaust gas recirculation (EGR) valve, and fuel delivery system. This means the check engine light is more likely to come on due to a sensor issue or vacuum leak than a major mechanical failure. Still, it’s important to address these codes promptly—ignoring them can lead to reduced fuel efficiency, increased emissions, or even engine damage over time.

The Role of the ECM in 1987 Vehicles

The engine control module (ECM) in a 1987 vehicle is the brain behind the check engine light. It constantly monitors input from various sensors and compares the data to expected values. If something falls outside the normal range—like a faulty oxygen sensor sending incorrect readings—the ECM logs a trouble code and turns on the check engine light.

The ECM in these older vehicles is relatively simple compared to today’s systems. It doesn’t have the processing power to run complex algorithms or monitor hundreds of parameters. Instead, it focuses on a handful of critical functions: air-fuel ratio, ignition timing, and emissions control. When one of these systems malfunctions, the ECM responds by storing a code and illuminating the light.

One thing to keep in mind is that the ECM in 1987 cars doesn’t “learn” like modern systems. It doesn’t adapt to driving habits or adjust fuel maps dynamically. This means that once a problem is fixed, the ECM may still store the code until it’s manually cleared. That’s why it’s important to clear the codes after repairs—otherwise, the light might stay on even if the issue is resolved.

Tools You Need to Read 1987 Check Engine Light Codes

The beauty of reading check engine light codes in a 1987 vehicle is that you don’t need expensive equipment. In fact, the only tool you really need is a simple paperclip or a short piece of wire. That’s right—no scanner, no smartphone app, no subscription service. Just a basic jumper wire to connect two terminals in the diagnostic port.

For most 1987 GM vehicles, you’ll find the diagnostic connector under the dashboard on the driver’s side. It’s usually a small, rectangular plug with several pins. To read the codes, you’ll need to ground the “ALDL” (Assembly Line Diagnostic Link) connector by connecting the terminal labeled “GND” or “Ground” to the “Diagnostic” terminal. A straightened paperclip works perfectly for this.

Ford vehicles from 1987 often use a similar method, but the connector may be located under the hood near the battery or on the firewall. You’ll typically need to ground a specific pin to enter diagnostic mode. Chrysler models might require turning the ignition key on and off in a specific sequence to trigger the light flashes.

In addition to a jumper wire, it’s helpful to have a flashlight, especially if the diagnostic port is in a hard-to-reach spot. A notepad and pen are also useful for recording the flash sequences. And don’t forget a code reference guide—either printed or saved on your phone—so you can look up what each code means.

Alternative Tools and Tips

While a paperclip is the most common tool, some enthusiasts prefer using a dedicated OBD-I jumper wire with labeled pins. These are inexpensive and make the process even easier, especially if you’re working on multiple vehicles. You can find them online or at auto parts stores that cater to classic cars.

Another helpful tip is to wear safety glasses and gloves, especially if you’re working under the dashboard or near the engine. Even though the system is low-voltage, it’s always better to be safe. Also, make sure the vehicle is in park (or neutral for manual transmissions) and the parking brake is engaged before you start.

If you’re having trouble locating the diagnostic port, consult your owner’s manual or a repair guide specific to your make and model. Many classic car forums also have detailed photos and instructions for different vehicles. Don’t hesitate to ask for help—there’s a whole community of vintage car lovers who’ve been through this before.

Step-by-Step Guide to Reading Codes on a 1987 GM Vehicle

Let’s walk through the process of reading check engine light codes on a 1987 GM vehicle, such as a Chevrolet Camaro, Pontiac Firebird, or Oldsmobile Cutlass. This method works for most GM cars and trucks from that era, but always double-check your specific model.

Locate the ALDL Connector

The first step is to find the ALDL (Assembly Line Diagnostic Link) connector. In most 1987 GM vehicles, it’s located under the dashboard on the driver’s side, near the steering column. It’s a small, rectangular plug with six to ten pins. Look for a label that says “ALDL” or “Diagnostic.”

Once you’ve found it, inspect the pins. You’re looking for two specific terminals: one labeled “GND” (Ground) and another labeled “Diagnostic” or “A.” These are usually at opposite ends of the connector. If you’re unsure, refer to a wiring diagram for your vehicle.

Ground the Diagnostic Terminal

Take your paperclip or jumper wire and straighten it out. Insert one end into the “GND” terminal and the other into the “Diagnostic” terminal. This creates a circuit that tells the ECM to enter diagnostic mode.

Make sure the ignition is off when you insert the jumper. Once it’s in place, turn the ignition to the “ON” position—but don’t start the engine. The check engine light should begin to flash.

Read the Flash Sequence

Now, watch the check engine light carefully. It will flash a series of long and short pulses that represent the trouble codes. Each code is displayed as two digits. For example:

– One long flash, then three short flashes = Code 13
– Two long flashes, then five short flashes = Code 25

The flashes are separated by a brief pause. A long flash represents a “10,” and a short flash represents a “1.” So, two long flashes and three short flashes mean 20 + 3 = Code 23.

After the first code is displayed, there’s a longer pause before the next one begins. The ECM will cycle through all stored codes, then repeat the sequence. Write down each code as it appears.

Look Up the Code Meaning

Once you’ve recorded the codes, it’s time to find out what they mean. Code 13, for example, typically indicates a problem with the oxygen sensor circuit. Code 25 might point to a faulty coolant temperature sensor.

Use a 1987 GM-specific code chart to interpret the numbers. These are widely available online or in repair manuals. Some common codes include:

– Code 12: No distributor reference signal (often appears at startup and is normal)
– Code 14: Coolant temperature sensor low input
– Code 15: Coolant temperature sensor high input
– Code 21: Throttle position sensor high input
– Code 22: Throttle position sensor low input
– Code 33: Manifold absolute pressure (MAP) sensor high input
– Code 34: MAP sensor low input
– Code 42: Electronic spark timing (EST) circuit fault
– Code 44: Oxygen sensor lean indication
– Code 54: Fuel pump circuit low voltage

Remember, Code 12 is often displayed when you first turn on the ignition and is usually not a cause for concern. It confirms the system is working. But if other codes appear, they need attention.

Reading Codes on 1987 Ford and Chrysler Vehicles

While GM vehicles use the ALDL method, Ford and Chrysler have their own ways of retrieving check engine light codes. The process is similar—grounding a terminal or using a key sequence—but the details vary.

Ford Vehicles (EEC-IV System)

Most 1987 Ford vehicles use the EEC-IV (Electronic Engine Control, Fourth Generation) system. To read codes, you’ll need to locate the Self-Test Connector, usually found under the hood near the battery or on the driver’s side fender.

This connector has several pins, but you’ll focus on two: the “Signal Return” (SIG RTN) and “Self-Test Input” (STI). Use a jumper wire to connect these two pins.

With the ignition off, insert the jumper. Then turn the ignition to “ON.” The check engine light will begin to flash codes in a similar pattern to GM vehicles—long and short flashes representing digits.

Ford codes are also two-digit numbers. For example, one long flash and four short flashes = Code 14. Common Ford codes include:

– Code 11: System pass (no faults)
– Code 12: RPM too low during self-test
– Code 14: Ignition pickup fault
– Code 18: PIP circuit fault
– Code 21: Coolant temperature sensor out of range
– Code 41: Oxygen sensor indicates lean
– Code 51: Oxygen sensor circuit open
– Code 61: Oxygen sensor indicates rich

After reading the codes, remove the jumper and turn off the ignition.

Chrysler Vehicles (OBD-I System)

Chrysler vehicles from 1987 use a slightly different method. Instead of a jumper wire, you’ll use the ignition key to enter diagnostic mode.

Turn the ignition key to “ON” and “OFF” three times within five seconds, ending in the “ON” position. The check engine light will then flash the trouble codes.

Like other manufacturers, Chrysler uses two-digit codes. For example, two long flashes and three short flashes = Code 23. Common Chrysler codes include:

– Code 11: No ignition reference signal
– Code 12: Battery disconnected recently
– Code 13: MAP sensor voltage too high
– Code 14: MAP sensor voltage too low
– Code 15: No vehicle speed sensor signal
– Code 17: Engine coolant temperature below thermostat regulating temperature
– Code 21: Oxygen sensor circuit fault
– Code 22: Coolant temperature sensor out of range
– Code 23: Throttle position sensor voltage too low
– Code 24: Throttle position sensor voltage too high

After the codes are displayed, the system will repeat them. Write them down and refer to a Chrysler-specific code chart.

Common 1987 Check Engine Light Codes and What They Mean

Now that you know how to retrieve codes, let’s look at some of the most common issues that trigger the check engine light in 1987 vehicles. These problems are often related to emissions, sensors, or electrical connections.

Oxygen Sensor Faults (Codes 13, 44, 54, 41, 51)

The oxygen sensor monitors the amount of oxygen in the exhaust and helps the ECM adjust the air-fuel mixture. If it fails or sends incorrect data, the engine may run rich (too much fuel) or lean (too little fuel).

Symptoms include poor fuel economy, rough idle, or increased emissions. Replacing the oxygen sensor is usually straightforward and inexpensive. Make sure to use a sensor compatible with your vehicle’s year and engine.

Coolant Temperature Sensor Issues (Codes 14, 15, 21, 22)

The coolant temperature sensor tells the ECM how hot the engine is. If it malfunctions, the engine may not warm up properly or may run too rich or lean.

A faulty sensor can cause hard starting, poor performance, or overheating. Check the sensor’s resistance with a multimeter or replace it if it’s old or corroded.

Throttle Position Sensor Problems (Codes 21, 22, 23, 24)

The throttle position sensor (TPS) monitors the position of the throttle plate. If it fails, the ECM can’t accurately control fuel delivery or ignition timing.

Symptoms include hesitation, surging, or stalling. The TPS is usually located on the throttle body and can be adjusted or replaced.

MAP Sensor Faults (Codes 33, 34, 13, 14)

The manifold absolute pressure (MAP) sensor measures engine load by detecting vacuum in the intake manifold. A faulty MAP sensor can cause poor acceleration, rough idle, or stalling.

Check for vacuum leaks, damaged hoses, or a dirty sensor. Cleaning or replacing the MAP sensor often resolves the issue.

Ignition and Timing Issues (Codes 42, 18, 11)

Problems with the ignition system—such as a faulty distributor, pickup coil, or electronic spark timing—can trigger codes related to spark delivery.

These issues may cause misfires, hard starting, or reduced power. Inspect the distributor cap, rotor, and ignition wires for wear or damage.

How to Clear Check Engine Light Codes After Repair

Once you’ve diagnosed and fixed the problem, you’ll want to clear the trouble codes so the check engine light turns off. There are a few ways to do this, depending on your vehicle.

Method 1: Disconnect the Battery

The simplest way to clear codes is to disconnect the negative battery cable for about 10–15 minutes. This resets the ECM and erases stored codes.

Make sure to turn off all electrical accessories before disconnecting the battery. After reconnecting, start the engine and check if the light remains off.

Method 2: Use the Diagnostic Port

On some 1987 vehicles, you can clear codes by grounding the diagnostic terminal for a specific amount of time. For example, on GM vehicles, leave the jumper wire in place for 10–30 seconds after the codes are displayed.

Consult your vehicle’s service manual for the exact procedure. This method is less disruptive than disconnecting the battery and preserves radio presets and clock settings.

Method 3: Drive Cycle Reset

In some cases, the ECM will clear codes automatically after a certain number of error-free drive cycles. This means driving the vehicle under normal conditions without triggering the fault again.

While this method works, it’s slower and less reliable. It’s better to manually clear the codes after repairs to ensure the light turns off immediately.

Tips for Maintaining Your 1987 Vehicle’s Diagnostic System

Keeping your 1987 vehicle in good condition helps prevent check engine light issues. Here are some tips to maintain the diagnostic system and overall engine health.

Regular Sensor Checks

Inspect key sensors like the oxygen sensor, coolant temperature sensor, and MAP sensor during routine maintenance. Clean or replace them as needed.

Check for Vacuum Leaks

Vacuum leaks are a common cause of check engine light codes. Inspect hoses for cracks, loose connections, or dry rot. Replace damaged hoses promptly.

Use Quality Fuel and Oil

Poor-quality fuel or oil can affect sensor performance and engine operation. Stick to reputable brands and follow the recommended maintenance schedule.

Keep the ECM Clean and Dry

The ECM is usually located under the dashboard or in the engine bay. Make sure it’s protected from moisture, dirt, and extreme temperatures.

Document Your Repairs

Keep a log of any codes you’ve read, repairs you’ve made, and parts you’ve replaced. This helps track recurring issues and simplifies future troubleshooting.

Conclusion

Reading check engine light codes in a 1987 vehicle is a valuable skill that saves time and money. With just a paperclip and a few minutes, you can decode what your car is telling you and address issues before they become serious.

Whether you drive a GM, Ford, or Chrysler, the process is straightforward once you know the steps. Locate the diagnostic port, ground the correct terminal, and watch the light flash. Then, use a code chart to interpret the results and take action.

Remember, the check engine light is your car’s way of asking for help. By learning how to read its messages, you’re taking control of your vehicle’s health and ensuring it runs smoothly for years to come.

Frequently Asked Questions

Can I read 1987 check engine light codes without a scanner?

Yes, you can read codes manually using a paperclip or jumper wire to ground specific terminals in the diagnostic port. No scanner is needed for OBD-I systems.

What does Code 12 mean on a 1987 GM vehicle?

Code 12 indicates no distributor reference signal and often appears at startup. It’s usually normal and not a cause for concern.

How do I clear codes on a 1987 Ford?

Disconnect the negative battery cable for 10–15 minutes, or use the Self-Test Connector to reset the system after repairs.

Why is my check engine light still on after fixing the problem?

The ECM may still store the code until it’s manually cleared. Use the battery disconnect method or diagnostic port to reset the system.

Are 1987 check engine light codes the same across all brands?

No, GM, Ford, and Chrysler each have their own code sets and procedures. Always use a manufacturer-specific code chart.

Can a vacuum leak cause the check engine light to come on?

Yes, vacuum leaks can trigger codes related to the MAP sensor or oxygen sensor, leading to a illuminated check engine light.