Hard Failures
To prevent a false Diagnostic Trouble Code (DTC) from being stored in PCM memory, some malfunctions must be detected during 2 consecutive drive cycles. This applies to heated oxygen sensors (HO2S), fuel metering-related components, idle control system, Engine Coolant Temperature (ECT) sensor, Exhaust Gas Recirculation (EGR) system, Three-Way Catalytic (TWC) converter system, evaporative (EVAP) control system and other self-diagnostic functions. First occurrence of a detected malfunction is stored in PCM memory. If same malfunction is detected again after ignition switch is turned off and then back on, a hard failure DTC is stored and Malfunction Indicator Light (MIL) is turned on. MIL will remain on until detected malfunction is repaired. Malfunction can be determined by retrieving DTCs. See DIAGNOSTIC TROUBLE CODE IDENTIFICATION and RETRIEVING DIAGNOSTIC TROUBLE CODES .
Fail-Safe Function
If a sensor fails, PCM will substitute a preprogrammed value for sensor and continue engine operation. In this condition, engine will operate, but driveability will not be optimum.
Back-Up Function
When a malfunction is detected in PCM, fuel injection is controlled by an independent back-up system, permitting minimal driving.
Intermittent Failures
An intermittent failure means that a system may have had a malfunction, but is okay now. Intermittent failures may cause Malfunction Indicator Light (MIL) to flicker or illuminate and go out after intermittent fault goes away. Corresponding DTC will be retained in Powertrain Control Module (PCM) memory. Intermittent failures may be caused by sensor, connector or wiring-related problems. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
MALFUNCTION INDICATOR LIGHT
All models are equipped with a Malfunction Indicator Light (MIL). As a bulb check, light illuminates for about 2 seconds when ignition switch is turned to ON position and engine is not running. MIL also illuminates when a system failure has been detected and a corresponding DTC has been set in Powertrain Control Module (PCM) memory. Not all trouble codes will activate MIL. If MIL is on and no DTCs are in memory, problem may be intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
Malfunction Indicator Light (MIL)
On Civic, CR-V and Prelude, Diagnostic Trouble Codes (DTCs) can also be accessed by using MIL. Turn ignition switch to OFF position. On Civic, CR-V and Prelude, connect SCS Service Connector (07PAZ-0010100) to 2-pin service check connector. On Civic, service check connector is located under passenger-side of instrument panel. (Scheme 27) On CR-V, service check connector is located behind right side of center console. On Prelude, service check connector is located behind access cover on right side of center console.
On all models, turn ignition switch to ON position. Diagnostic Trouble Codes (DTCs) will be indicated by a series of long and short flashes on MIL. Number of long flashes indicate number in tens column. Number of short flashes indicate number in ones column. For example, 4 long flashes followed by 3 short flashes would indicate DTC 43. See DIAGNOSTIC TROUBLE CODE IDENTIFICATION and proceed to appropriate DTC testing in appropriate SELF-DIAGNOSTICS article.
Scheme 26
Scheme 27
FREEZE FRAME DATA
Freeze frame data indicates engine operating conditions when first malfunction, misfire or fuel trim malfunction was detected. Freeze frame data is read using a Honda PGM tester or OBD-II scan tool. Follow manufacturer's instructions.
SUBSTITUTING PCM
Note. When replacing PCM, program new PCM and both Black and Gray ignition keys using Honda PGM Tester and Immobilizer program card.
- This procedure allows swapping PCM without having to program test vehicle's ignition key on a vehicle equipped with immobilizer system. Cut a temporary ignition key for test vehicle from a non-immobilizer key blank. Remove PCM from test vehicle.
- Write test vehicle's VIN on removed PCM to avoid confusion. Install known-good PCM in to test vehicle. Tape head of ignition key belonging to known-good PCM to head of temporary key. This will allow known-good PCM to recognize immobilizer code and allow engine to start using temporary key. After completing test, destroy temporary key.
SUMMARY
If MIL does not illuminate, indicating a Diagnostic Trouble Code (DTC) has been set and there is a driveability malfunction, go to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures. Some troubleshooting steps may require resetting PCM and attempting to duplicate DTC. If malfunction is intermittent and DTC cannot be duplicated, discontinue troubleshooting procedures and go to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom. If DTC cannot be duplicated, continuing with troubleshooting procedures will cause confusion and could result in unnecessary component replacement.