Experiencing a check engine light in your 97 Honda Civic EX can be unsettling. Understanding what those lights and OBD2 codes mean is crucial for any car owner. This guide is specifically designed to help you, the 97 Honda Civic EX owner, navigate the world of OBD2 codes, diagnose potential issues, and potentially save money by understanding your vehicle’s diagnostic messages.
Before the standardization of OBD-II (On-Board Diagnostics II), deciphering Check Engine Light (CEL) or Malfunction Indicator Light (MIL) codes was a complex task, often requiring dealership visits or specialized tools. Thankfully, with OBD2, things became significantly easier. Many believe that diagnosing a 1996 or later vehicle necessitates a trip to a professional mechanic or the use of an expensive OBD-II scan tool. However, for your 97 Honda Civic EX, this isn’t entirely true. You can actually access your OBD2 codes yourself with a simple paperclip!
Let’s dive into how you can retrieve these codes and what they signify for your 97 Honda Civic EX.
Decoding Your 97 Honda Civic EX OBD2 Codes Manually
Yes, you read that right. For your 97 Honda Civic EX, you can retrieve the OBD2 codes without a scan tool. The OBD-II connector is conveniently located under the driver’s side dashboard. By using a paperclip, as illustrated in the images below, you can initiate the process to read these codes.
This method works because the OBD-II system on your 97 Honda Civic EX, while standardized, still retains the capability for basic code retrieval without specialized equipment. But to fully appreciate this, let’s understand what OBD-II is all about.
Understanding OBD-II Systems
OBD-II is more than just a diagnostic port; it’s a standardized system that revolutionized vehicle diagnostics. Think of it as an international language for cars to communicate about their health. Before OBD-II, each car manufacturer had proprietary systems, making diagnostics complicated and often brand-specific.
OBD-II, detailed in the SAE On-Board Diagnostics for Light and Medium Duty Vehicles Standards Manual, standardized several key aspects:
- Diagnostic Trouble Codes (DTCs): A universal set of codes to identify problems.
- Data Port Connector: A standardized connector shape and location, typically within three feet of the driver and easily accessible.
Prior to OBD-II, accessing diagnostic information was often cumbersome. Methods included complex key-turning sequences and interpreting “Morse code” like blinks from the check engine light. On older Hondas, mechanics had to locate the Engine Control Module (ECM) and count LED blinks to decipher codes – a time-consuming and error-prone process.
OBD-II simplified this drastically. Now, all codes follow a consistent format, and the access point is always in the same general location, making diagnostics much more user-friendly.
Deciphering Common OBD2 Misconceptions
A common misconception is that a Check Engine Light always indicates a loss of engine power. This isn’t necessarily true. OBD-II primarily uses the CEL/MIL to signal issues that directly affect vehicle emissions. For example, a faulty oxygen sensor downstream of the catalytic converter will trigger the MIL, even though this sensor doesn’t directly control fuel, spark, or boost. The ECM interprets this as a catalytic converter inefficiency issue.
While many faults trigger the MIL immediately, some require recurring instances. It’s also possible to experience a performance issue without the MIL being illuminated, highlighting that the system isn’t foolproof.
Limp Home Mode: An OBD-II Safety Feature
One of the significant benefits of OBD-II is its contribution to vehicle reliability through “limp home” mode. In older vehicles, a disconnected Mass Air Flow (MAF) sensor could lead to engine stalling or uncontrolled fuel delivery. OBD-II equipped vehicles, like your 97 Honda Civic EX, are smarter. If the MAF sensor is disconnected, the computer uses data from other sensors like RPM, throttle position, and MAP sensor to keep the engine running in a reduced power “limp home” mode.
OBD-II systems also incorporate logic checks. For instance, if the coolant temperature sensor readings become erratic (e.g., suddenly dropping from 200°F to -30°F), the ECM recognizes a sensor malfunction and defaults to a safe value (e.g., 176°F) for fuel and spark calculations.
Another clever feature protects the catalytic converter. If excessive misfires are detected in a cylinder, raw fuel entering the exhaust can overheat and damage the catalytic converter. OBD-II systems can detect this and temporarily disable the fuel injector to the affected cylinder.
Aftermarket Modifications and OBD2 Systems
While generally robust, OBD-II systems can be sensitive to aftermarket modifications, particularly those that interfere with sensor data. Simple bolt-on modifications like exhaust systems usually don’t cause issues. However, some aftermarket downpipes might trigger a Check Engine Light if they don’t maintain sufficient heat for the catalytic converter to function optimally. The general rule is to avoid directly altering sensor data when dealing with OBD-II systems.
Understanding Diagnostic Trouble Codes (DTCs)
DTCs are the language of OBD-II. They are five-digit alphanumeric codes. Let’s break down the structure:
- First Character (Letter): Indicates the system group (e.g., P for Powertrain, B for Body, C for Chassis, U for Network).
- Second Character (Number): 0 for generic OBD-II code, 1 or 2 for manufacturer-specific code.
- Third Character (Number): Indicates the subsystem (e.g., 1 for Fuel and Air Metering, 2 for Fuel and Air Metering – Injector Circuit, 3 for Ignition System or Misfire, etc.).
- Last Two Characters (Numbers): Specific fault number.
“Generic” DTCs are standardized across all vehicles, ensuring a baseline level of diagnostic consistency. For example, P0115, a generic code, refers to “Engine Coolant Temperature Circuit Malfunction.” However, there can be numerous related codes, such as P0116 “Engine Coolant Temperature Circuit Range/Performance Problem,” illustrating the system’s detail.
A single sensor malfunction can sometimes trigger multiple DTCs. A faulty oxygen sensor might result in codes P0130, P0131, and P0133. Often, replacing the sensor resolves all related codes.
Limp Mode Triggers: Sensor Failures
Several sensor malfunctions can trigger limp home mode in your 97 Honda Civic EX. Here are some key sensors and their generic DTCs associated with limp mode:
- Mass Air Flow (MAF), Mass Air Sensor (MAS), Vane Air Flow (VAF), Manifold Absolute Pressure (MAP) Sensor: ECM uses throttle position and RPM for basic fuel delivery; disables idle control. Generic DTC: P0100
- Intake Air Temperature (IAT) Sensor: ECM assumes a constant air temperature of 25°C/77°F. Generic DTC: P0110
- Throttle Position Sensor (TPS): Disables temporary fuel enrichment during acceleration, potentially causing hesitation. Generic DTC: P0120
- Engine Coolant Temperature (ECT) Sensor: ECM assumes a coolant temperature of 80°C/176°F. Generic DTC: P0115
- Camshaft Position (CMP) Sensor: On 4-cylinder engines, runs injectors in a 1-3-4-2 firing order with irregular timing; fuel supply shuts off after four seconds if no signal. Generic DTC: P0340
- Barometric Pressure Sensor (BARO): Assumes sea-level atmospheric pressure (101 kPa/30 inches Hg). Generic DTC: P0105
- Crankshaft Knock Sensor (CKF): Switches ignition timing to a low-octane profile; turbo cars may reduce boost. Generic DTC: P0325
- Cylinder Misfire: Fuel supply to the misfiring cylinder is shut off. Generic DTC: P0300
- Exhaust Gas Oxygen (EGO) Sensor – Front: EGO sensor is disregarded for fuel trim correction; ECM relies on lookup tables. Generic DTC: P0130
- Exhaust Gas Oxygen (EGO) Sensor – Rear: While not causing power loss, it illuminates the MIL. The rear sensor monitors catalytic converter efficiency. Generic DTC: P0130
- Turbocharger Wastegate Actuator: If boost pressure is excessive, fuel is cut until boost decreases. Generic DTC: P0243
Information above within this section is courtesy of Overboost.com
97 Honda Civic EX OBD2 and CEL Code List
Here’s a comprehensive list of OBD2 codes and corresponding CEL codes specific to your 97 Honda Civic EX. This table combines both OBD-II standard codes and the older CEL codes for your convenience.
OBD-II Codes & CEL Equivalents for 97 Honda Civic EX
| MIL (CEL) Code | OBDII Code | Description of Code |
|---|---|---|
| P0106 | MAP Circuit Range Or Performance | |
| P0107 | MAP Circuit Low Input | |
| 3 | P0107 | MAP Circuit Low Input |
| P0108 | MAP Circuit High Input | |
| 3 | P0108 | MAP Circuit High Input |
| P0111 | IAT Sensor Circuit Range/Performance | |
| 10 | P0111 | IAT Sensor Circuit Range/Performance |
| P0112 | IAT Sensor Circuit Low Input | |
| 10 | P0112 | IAT Sensor Circuit Low Input |
| P0113 | IAT Sensor Circuit High Input | |
| 10 | P0113 | IAT Sensor Circuit High Input |
| P0116 | ECT Circuit Range Or Performance | |
| 86 | P0116 | ECT Circuit Range Or Performance |
| P0117 | ECT Circuit Low Input | |
| 6 | P0117 | ECT Circuit Low Input |
| P0118 | ECT Circuit High Input | |
| 6 | P0118 | ECT Circuit High Input |
| P0122 | TP Sensor Circuit Low Input | |
| 7 | P0122 | TP Sensor Circuit Low Input |
| P0123 | TP Sensor Circuit High Input | |
| 7 | P0123 | TP Sensor Circuit High Input |
| 1 | P0131 | Primary HO2S Circuit Low Voltage (Sensor 1) |
| 1 | P0132 | Primary HO2S Circuit High Voltage (Sensor 1) |
| 61 | P0133 | Primary HO2S Circuit Slow Response (Sensor 1) |
| 41 | P0135 | Front HO2S Heater Circuit Fault (Sensor 1) |
| 63 | P0137 | Secondary HO2S Circuit Low Voltage (Sensor 2) |
| 63 | P0138 | Secondary HO2S Circuit High Voltage (Sensor 2) |
| 63 | P0139 | Secondary HO2S Circuit Slow Response (Sensor 2) |
| 65 | P0141 | Secondary HO2S Heater Circuit Fault (Sensor 2) |
| 45 | P0171 | System Too Lean |
| 45 | P0172 | System Too Rich |
| — | P0300 | Random Misfire |
| P0300 | Random Misfire | |
| 71 | P0301 | Misfire Cyl. 1 Or Random Misfire |
| 72 | P0302 | Misfire Cyl. 2 Or Random Misfire |
| 73 | P0303 | Misfire Cyl. 3 Or Random Misfire |
| 74 | P0304 | Misfire Cyl. 4 Or Random Misfire |
| 75 | P0305 | Misfire Cyl. 5 Or Random Misfire |
| 76 | P0306 | Misfire Cyl. 6 Or Random Misfire |
| 23 | P0325 | KS Circuit Malfunction |
| 4 | P0335 | CKP Sensor Circuit Low Input |
| 4 | P0336 | CKP Sensor Range/Performance |
| 80 | P0401 | EGR Insufficient Flow Detected |
| 67 | P0420 | Catalyst System Efficiency Below Threshold |
| 92 | P0441 | EVAP Emission Control System Improper Purge Flow |
| 91 | P0451 | Fuel Tank Pressure Sensor Range/Performance |
| 91 | P0452 | Fuel Tank Pressure Sensor Circuit Low Input |
| 91 | P0453 | Fuel Tank Pressure Sensor Circuit High Input |
| 17 | P0500 | VSS Circuit Malfunction (M/T) |
| 17 | P0501 | VSS Circuit Range/Performance (A/T) |
| 14 | P0505 | ICS Malfunction |
| 34 | P0560 | Powertrain Control Module (PCM) Backup Voltage Circuit Low Voltage |
| 70 | P0700, P0715, P0720, P0725, P0730, P0740, P0753, P0758, P0763, P0780 | A/T Concerns |
| 13 | P1106 | BARO Circuit Range/Performance |
| 13 | P1107 | BARO Circuit Low Input |
| 13 | P1108 | BARO Circuit High Input |
| 7 | P1121 | Throttle Position Lower Than Expected |
| 7 | P1122 | Throttle Position Higher Than Expected |
| 5 | P1128 | MAP Lower Than Expected |
| 5 | P1129 | MAP Higher Than Expected |
| 61 | P1149 | Primary HO2S (Sensor 1) Circuit Range/Performance Problem |
| 48 | P1162 | Primary HO2S (No. 1) Circuit Malfunction |
| 61 | P1163 | Primary HO2S (No. 1) Circuit Slow Response |
| 61 | P1164 | Primary HO2S (No. 1) Circuit Range/Performance |
| 61 | P1165 | Primary HO2S (No. 1) Circuit Range/Performance |
| 41 | P1166 | Primary HO2S (No. 1) Heater System Electrical |
| 41 | P1167 | Primary HO2S (No. 1) Heater System |
| 48 | P1168 | Primary HO2S (No. 1) LABEL Low Input |
| 48 | P1169 | Primary HO2S (No. 1) LABEL High Input |
| 21 | P1253 | VTEC System Malfunction |
| 22 | P1257, P1258, P1259 | VTEC System Malfunction |
| 20 | P1297 | Electrical Load Detector Circuit Low Input |
| 20 | P1298 | Electrical Load Detector Circuit High Input |
| 71–74 | P1300 | Multiple Cylinder Misfire Detected |
| P1300 | Multiple Cylinder Misfire Detected | |
| 54 | P1336 | CSF Sensor Intermittent Interruption |
| 54 | P1337 | CSF Sensor No Signal |
| 8 | P1359 | CKP/TDC Sensor Connector Disconnection |
| 8 | P1361 | TDC Sensor Intermittent Interruption |
| 8 | P1362 | TDC Sensor No Signal |
| 58 | P1366 | TDC Sensor No. 2 Intermittent Interruption |
| 58 | P1367 | TDC Sensor No 2 Signal |
| 9 | P1381 | Cylinder Position Sensor Intermittent Interruption |
| 9 | P1382 | Cylinder Position Sensor No Signal |
| 90 | P1456 | EVAP Emission Control System Leak Detected (Fuel Tank System) |
| 90 | P1457 | EVAP Emission Control System Leak Detected (Control Canister System) |
| 92 | P1459 | EVAP Emission Purge Flow Switch Malfunction |
| — | P1486 | Thermostat Range/Performance Problem |
| P1486 | Thermostat Range/Performance Problem | |
| 12 | P1491 | EGR Valve Lift Insufficient Detected |
| 12 | P1498 | EGR Valve Lift Sensor High Voltage |
| 14 | P1508 | IAC Valve Circuit Failure |
| 14 | P1509 | IAC Valve Circuit Failure |
| 14 | P1519 | Idle Air Control Valve Circuit Failure |
| — | P1607 | ECM/PCM Internal Circuit Failure A |
| 30 | P1655 | SEAF/SEFA/TMA/TMB Signal Line Failure |
| 70 | P1660 | A/T FI Signal A Circuit Failure |
| — | P1676 | FPTDR Signal Line Failure |
| — | P1678 | FPTDR Signal Line Failure |
| 30 | P1681 | A/T FI Signal A Low Input |
| 30 | P1682 | A/T FI Signal A High Input |
| 31 | P1686 | A/T FI Signal B Low Input |
| 31 | P1687 | A/T FI Signal B High Input |
| 70 | P1705, P1706, P1738, P1739, P1753, P1758, P1768, P1773, P1785, P1786, P1790, P1791, P1792, P1793, P1794 | A/T Concerns |
| 70 | P1870, P1873, P1879, P1885, P1886, P1888, P1890, P1891 | A/T Concerns |
Code information compiled from various internet sources.
CEL Code Definitions for 97 Honda Civic EX
For quick reference, here are the definitions of the CEL codes specifically for your 97 Honda Civic EX:
| CODE | DEFINITION |
|---|---|
| 1 | Oxygen Sensor “A” (Primary) defective circuit or unplugged / defective sensor |
| 2 | Oxygen Sensor “B” defective circuit or unplugged / defective sensor |
| 3 | MAP Sensor (Manifold Absolute Pressure) defective circuit or unplugged / defective sensor |
| 4 | CKP Sensor (Crankshaft Position Sensor) defective circuit or unplugged / defective sensor |
| 5 | MAP Sensor (Manifold Absolute Pressure) mechanical problem / disconnected piping * not 94-95 |
| 6 | ECT Sensor (Engine Coolant Temperature) defective circuit or unplugged / defective sensor |
| 7 | TP Sensor (Throttle Position) defective circuit or unplugged / defective sensor |
| 8 | TDC Sensor (Top Dead Center) defective circuit or unplugged / defective sensor |
| 9 | CYP Sensor (Cylinder) defective circuit or unplugged / defective sensor * invalid code for throttle body injection Hondas ** invalid code for V6 engines |
| 10 | IAT Sensor (Intake Air Temperature) defective circuit or unplugged / defective sensor |
| 12 | EGR Lift Sensor (Exhaust Gas Recirculation) defective circuit or unplugged / defective sensor * invalid code for non-equipped EGR valve vehicles |
| 13 | BARO Sensor (Atmospheric Pressure) defective circuit or unplugged / defective sensor |
| 14 | IAC Valve (Idle Air Control) defective circuit or unplugged / defective sensor |
| 15 | Ignition Output Signal missing or defective ignition output signal |
| 16 | Fuel Injector System defective circuit or unplugged / defective fuel injector |
| 17 | VSS (Vehicle Speed Sensor) defective circuit or unplugged / defective sensor |
| 19 | Automatic Transmission Lock Up Control Solenoid Valve defective circuit or unplugged / defective solenoid valve |
| 20 | Electrical Load Detector defective circuit or unplugged / defective sensor |
| 21 | VTEC Solenoid Valve defective circuit or unplugged / defective solenoid valve * invalid code for non-VTEC engine ** invalid for V6 engine |
| 22 | VTEC Oil Pressure Switch defective circuit or unplugged / defective oil pressure switch * invalid code for non-VTEC engine |
| 23 | KS (Knock Sensor) defective circuit or unplugged / defective sensor * invalid code for V6 engine |
| 30 | Automatic Transmission Signal: “A” / SEAF / SEFA / TMA or TMB defective circuit or unplugged / defective sensor * invalid code for 1996 |
| 31 | Automatic Transmission Signal “B” defective circuit or unplugged / defective sensor |
| 41 | Primary Oxygen Sensor – Heater circuit malfunction |
| 43 | Fuel Supply System defective or malfunctioning fuel supply system |
| 45 | System Too Lean or Too Rich malfunction in the fuel monitoring systems |
| 48 | LAF Sensor (Lean Air Fuel) defective circuit or unplugged / defective sensor |
| 54 | CKF Sensor (Crankshaft Speed Fluctuation) defective circuit or unplugged / defective sensor |
| 61 | Oxygen Sensor, Heated – Sensor 1 (Primary) high voltage, low voltage, or slow response |
| 63 | Oxygen Sensor, Heated – Sensor 2 (Secondary) high voltage, low voltage, or slow response |
| 65 | Oxygen Sensor Heater (Secondary) malfunctioning or defective oxygen sensor heater |
| 67 | Catalyst system Efficiency Below Threshold malfunctioning or defective catalyst system |
| 70 | Automatic Transmission malfunction with the automatic transmission controls |
| 71 | Cylinder 1 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire |
| 72 | Cylinder 2 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire |
| 73 | Cylinder 3 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire |
| 74 | Cylinder 4 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire |
| 80 | Exhaust Gas Recirculation insufficient flow detected |
| 86 | ECT Sensor (Engine Coolant Temperature) circuit range / performance problem |
| 90 | Evaporative Emission Control System leak detected in the fuel tank area |
| 91 | Fuel Tank Pressure Sensor low input |
| 92 | Evaporative Emission Control System insufficient purge flow |
Code definitions compiled from various internet sources.
Conclusion
Understanding the OBD2 codes for your 97 Honda Civic EX empowers you to take a more active role in your car’s maintenance. While this guide provides a starting point, remember that diagnosing car problems can be complex. If you are unsure about a code or the repair process, it’s always best to consult a qualified mechanic. However, with this knowledge, you are now better equipped to understand your 97 Honda Civic EX and address those pesky check engine lights!
For further information, you can explore resources like http://www.obd-codes.com/trouble_codes/.
