Honda vehicles manufactured before the widespread adoption of OBD2 (On-Board Diagnostics II) in 1996 utilize a different system for diagnosing engine problems. Understanding these pre-OBD2 codes is crucial for effectively troubleshooting and repairing these older Honda models. This guide provides a comprehensive list of Honda pre-OBD2 codes, covering both engine (CEL) and transmission (TCU) trouble codes.
Decoding Honda Engine (CEL) Codes
Pre-OBD2 Honda engine trouble codes are typically two-digit numeric codes. Here’s a breakdown of common codes:
- Code 1: O2A – Oxygen Sensor #1: Indicates a problem with the primary oxygen sensor, affecting fuel mixture and engine performance.
- Code 2: O2B – Oxygen Sensor #2: Signals an issue with the secondary oxygen sensor (if equipped), primarily used for catalytic converter monitoring.
- Code 3 & 5: MAP – Manifold Absolute Pressure Sensor: Points to a faulty MAP sensor, which measures intake manifold pressure to determine engine load.
- Code 4: CKP – Crank Position Sensor: A critical sensor for ignition timing and fuel injection. This code indicates a potential failure requiring immediate attention.
- Code 7: TPS – Throttle Position Sensor: This code signifies a problem with the TPS, which informs the ECU of throttle opening, impacting acceleration and fuel delivery.
- Code 10: IAT – Intake Air Temperature Sensor: A faulty IAT sensor can lead to incorrect air/fuel mixture calculations.
- Code 14: IAC (EACV) – Idle Air Control Valve: Issues with the IAC valve can cause rough idling, stalling, or high idle speeds.
- Code 21 & 22: VTEC Solenoid Valves: These codes relate to the Variable Valve Timing and Lift Electronic Control system, often indicating solenoid malfunction.
- Code 41: Primary Oxygen Sensor Heater: Suggests a problem with the heating element of the primary oxygen sensor.
- Code 43: Fuel Supply System: A general code indicating a problem within the fuel system. Further diagnosis is needed.
Understanding Honda Transmission (TCU) Codes
Honda pre-OBD2 TCU codes are also numeric, often indicating issues with various transmission components:
- Code 1 & 2: Lock-up Solenoid Circuit: These codes relate to the lock-up torque converter, potentially causing issues with fuel efficiency and shifting.
- Code 3: Throttle Position Sensor Circuit: Similar to the engine code, this indicates a problem with the TPS signal reaching the TCU.
- Code 4: Vehicle Speed Sensor: A faulty VSS can cause erratic shifting and speedometer malfunctions.
- Code 7 & 8: Shift Solenoid Circuit: Problems with shift solenoids can result in harsh or delayed shifting.
Utilizing the Codes for Diagnostics
These codes serve as a starting point for diagnosing problems. Consult a Honda repair manual specific to your vehicle’s year and model for detailed diagnostic procedures and troubleshooting steps. A code reader designed for pre-OBD2 Honda systems is necessary to retrieve these codes. Remember that these codes may not pinpoint the exact problem but rather guide you towards the affected system or component.
