Honda Prelude Si 1993 - 1993 ENGINE PERFORMANCE Self-Diagnostics

Honda Prelude Si 1993 - INTRODUCTION

If no faults were found while performing BASIC TESTING , proceed with self-diagnostics. If no Diagnostic Trouble Codes (DTCs) or only pass codes are present after entering self-diagnostics, proceed to TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).

Honda Prelude Si 1993 - SELF-DIAGNOSTIC SYSTEM Hard Failures

Hard failures cause Malfunction Indicator Light (MIL) to illuminate and remain on until problem is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined by retrieving DTCs and using TROUBLE CODE CHARTS. See RETRIEVING CODES . If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, the vehicle runs but driveability will not be optimum.

Honda Prelude Si 1993 - Intermittent Failures

Intermittent failures may cause Malfunction Indicator light (MIL) to flicker or illuminate and go out after the intermittent fault goes away. The corresponding DTC will be retained in ECM memory. If related fault does not reoccur within 50 starter operations, related DTC will be erased from control unit memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Honda Prelude Si 1993 - MALFUNCTION INDICATOR LIGHT (MIL)

All models are equipped with an MIL. As a bulb check, light illuminates when ignition is on and engine is not running. MIL also illuminates when a system failure has been detected and a corresponding DTC has been set in ECM memory. Not all trouble codes will activate MIL. If MIL is on and no DTCs are in memory, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Honda Prelude Si 1993 - RETRIEVING CODES

With ignition off, insert jumper wire in service check connector terminals, located near center console on Prelude. See Fig. 1 . Turn ignition switch to ON position. Diagnostic Trouble Codes (DTCs) will be indicated by a series of long and short flashes on MIL. The number of long flashes indicates the number in the 10s column. The number of short flashes indicates the number in the 1s column. For example, 4 long flashes followed by 3 short flashes would indicate DTC 43.

See TROUBLE CODE DEFINITION table and proceed to appropriate TROUBLE CODE CHART for testing. All voltage tests should be performed with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless specifically stated differently in testing procedure.

Fig. 1: Honda Prelude Si 1993 - Component Locations - Locating Service Check Connectors, Prelude

Honda Prelude Si 1993 - DIAGNOSTIC TROUBLE CODE DEFINITION

Honda Prelude Si 1993 DIAGNOSTIC TROUBLE CODE IDENTIFICATION

Code ⁽¹⁾

System Affected

Probable Cause

No Code

ECM

No Signal To ECM

Heated Oxygen Sensor (HO2S)

Problem In HO2S Circuit

MAP Sensor

Electrical Problem In MAP Sensor

Crank Angle Sensor (CKP)

Open Or Shorted Signal Circuit

MAP Sensor

Mechanical Problem In MAP Sensor

Engine Coolant Temperature (ECT) Sensor

Open Or Shorted Signal Circuit

Throttle Position (TP) Sensor

Open Or Shorted Signal Circuit

Crank Angle Sensor (TDC)

Open Or Shorted Signal Circuit

Crank Angle Sensor (CYP)

Open Or Shorted Signal Circuit

Intake Air Temperature(IAT)

Problem With Sensor

EGR System

No EGR Action

Barometric Pressure (BARO) Sensor

Problem With PA Circuit

Idle Air Control(IAC) Valve

Open Or Shorted Signal Circuit

Ignition Output Signal

Electrical Problem In Signal Circuit

Fuel Injector

Problem In Fuel Injector Circuit

Vehicle Speed Sensor (VSS)

Open Or Shorted Signal Circuit

Electrical Load Detector (ELD)

Problem With ELD Circuit

Knock Sensor (Prelude)

Problem With Knock Sensor Circuit

A/T FI Signal A

Problem In A/T Control Unit And ECM Circuit

A/T FI Signal B

Problem In A/T Control Unit And ECM Circuit

Heated Oxygen Sensor (HO2S) Heater

Problem With HO2S Circuit

Fuel Supply System

Problem With HO2S Circuit Or Fuel System

⁽¹⁾

If codes other than these are indicated, repeat self-diagnosis. If code(s) reappear, substitute a known good ECM, and recheck codes. If code(s) clear, replace ECM.

Honda Prelude Si 1993 - ECM RESET PROCEDURE/CLEARING CODES

NOTE:

Some models have an anti-theft code built into the radio circuit. Clearing codes cancels clock and radio settings; make note of settings before beginning reset procedure. After ECM reset, the radio will not function until code is entered.

To reset ECM, remove BACK UP fuse (CLOCK/RADIO fuse on Prelude) from underhood fuse/relay block. Leave fuse out for 10 seconds to reset ECM.

Honda Prelude Si 1993 - ECM LOCATION

ECM is located under carpet in passenger-side footwell. See Fig. 1 .

Honda Prelude Si 1993 - SUMMARY

If no hard trouble codes (or only pass codes) are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedure.

Honda Prelude Si 1993 - DIAGNOSTIC TROUBLE CODE CHARTS

NOTE:

In the following diagnostic trouble code charts, illustrations and schematics are courtesy of American Honda Motor Co., Inc.

Honda Prelude Si 1993 - Using Diagnostic Trouble Code Charts

To use DIAGNOSTIC TROUBLE CODE CHARTS, see RETRIEVING CODES under SELF-DIAGNOSTIC SYSTEM. After codes have been recorded, proceed to appropriate DIAGNOSTIC TROUBLE CODE CHART.

When directed by chart to install ECM test harness, turn ignition off. Connect ECM Test Harness (07LAJ-PT3010A ) between ECM and connector. See Fig. 2 . Follow code chart directions.