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Engine Controls - System/component Tests: Diagnosis Honda Prelude IV

Testing & Diagnostics ~420 words

Voltage Test

  1. Connect test harness between ECM and main wiring harness. (Схема №4) Unplug connector "B" from main harness, but not from ECM. Turn ignition on. Measure voltage between terminals A26 and B5. (Схема №3)
  2. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, substitute known-good ECM and retest system. If voltage is now about 5 volts, replace ECM. If voltage is still not about 5 ohms, check and repair wiring between A/C switch and ECM. See «WIRING DIAGRAMS»(/honda/prelude/iv-1992-1996/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article in this section.
  3. Turn ignition off. Reconnect main harness. Turn ignition on. Momentarily connect ECM terminals A15 and A26 together. If A/C clutch does not click, go to next step. If clutch clicks, start engine and turn A/C on. If A/C operates, A/C signal exists. If A/C does not operate, go to step 5).
  4. Using jumper, connect Red/Blue wire from A/C compressor control unit to chassis ground. See «WIRING DIAGRAMS»(/honda/prelude/iv-1992-1996/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article in this section. If A/C clutch clicks, repair open circuit between ECM and A/C compressor control unit. If clutch does not click, repair A/C system. See the «A/C-HEATER SYSTEM - MANUAL»(ref-26371) article.
  5. With engine running and A/C on, measure voltage between terminals A26 and B5. If voltage is less than one volt, substitute a known-good ECM. If A/C now functions, replace ECM. If voltage is greater than one volt, repair open circuit between ECM and A/C switch. See «WIRING DIAGRAMS»(/honda/prelude/iv-1992-1996/remont/wiring-diagrams-engine-performance/#wiring-diagrams) article in this section.

Resistance Test

Start engine and warm it to normal operating temperature. Unplug sensor connector. Sensor is located on front of engine, near distributor. Measure resistance between sensor terminals. If resistance is not 200-400 ohms, replace sensor.

Unplug sensor connector. Sensor is located at top of engine, on left side. Measure resistance between sensor terminals. Resistance should be as specified. See INTAKE AIR TEMPERATURE (IAT) SENSOR RESISTANCE table. If resistance is not within specification, replace sensor.

Temperature - °F (°C)Ohms
4 (-20)15,000-18,000
68 (20)1000-4000
176 (80)200-400

INTAKE AIR TEMPERATURE (IAT) SENSOR RESISTANCE

  1. Connect test harness between ECM and main harness. (Схема №4) Turn ignition on. Measure voltage between terminals D17 and D21. (Схема №3)
  2. If voltage is about 3 volts, go to Vacuum Test. If voltage is not about 3 volts, check wiring between sensor and ECM for continuity or shorts. If wiring is okay, replace MAP sensor.

Vacuum Test

Connect vacuum pump to MAP sensor. The MAP sensor is located at top center of firewall. Apply vacuum. If MAP sensor does not hold vacuum, replace sensor.

See also:
• WIRING DIAGRAMS

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