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Test II - Exhaust Heat Control (EHC)

  1. Use only VOM/DVOM, not STAR tester, for this step. Turn key OFF and wait 10 seconds. Set DVOM to 20 volt scale. Connect negative lead of DVOM to STO and positive lead to positive battery terminal. Jumper STI to signal return. Run KOEO Self-Test until end of continuous codes. DVOM should read 0 volts. Depress and release throttle while watching DVOM reading. If reading changes to high voltage, remain in Output State check and go to next step. If reading did not change to a high voltage, depress throttle to WOT position and release. If STO voltage does not go to high reading, go to Circuit Test NN, step 13). Leave equipment hooked up.
  2. Set DVOM set to 20 volt scale. Measure voltage between VPWR and EHC circuit at EHC solenoid. While observing DVOM, depress and release throttle several times to cycle EHC output ON and OFF. If DVOM reading shows EHC output cycling, go to next step. If EHC output does not show cycling on DVOM, remove jumper wire and go to step 5).
  3. Install vacuum pump to exhaust heat solenoid vacuum supply port and install vacuum gauge to output port. Apply 6 in. Hg, minimum. With vacuum applied, observe vacuum gauge while cycling outputs ON and OFF by depressing and releasing throttle. If vacuum output cycles ON and OFF, go to next step. If vacuum output does not cycle ON and OFF, replace solenoid and repeat QUICK TEST.
  4. With vacuum lines disconnected at EHC solenoid, start engine and check for vacuum. If vacuum is present, EEC-IV system is good, check EHC. If no vacuum is present, remove vacuum source blockage or repair vacuum leak and repeat QUICK TEST.
  5. Turn key OFF and wait 10 seconds. Set DVOM to 200 ohm scale. Disconnect EHC solenoid connector and measure solenoid resistance. If resistance is between 50-100 ohms, connect EHC solenoid and go to next step. If resistance is less than 50 ohms or greater than 100 ohms, replace HEC solenoid and repeat QUICK TEST.
  6. Turn key ON, leaving engine OFF. With DVOM on 20 volt scale, measure voltage at EHC solenoid harness connector between VPWR circuit and ground. If voltage reading is 10.5 volts or less, repair open circuit in harness and repeat QUICK TEST. If voltage reading is 10.5 volts or greater, go to next step.
  7. Turn key OFF and wait 10 seconds. Disconnect 60-pin ECA connector. Inspect for and repair any damaged wiring. Connect breakout box, leaving ECA disconnected. Set DVOM to 200 ohm scale. Measure resistance between test pin 55 and EHC circuit at harness connector. If resistance reading is 5 ohms or greater, repair open circuit in harness and repeat QUICK TEST. If resistance reading is less than 5 ohms, go to next step.
  8. Turn key OFF and wait 10 seconds. Leave breakout box connected and ECA disconnected. Disconnect EHC solenoid. Set DVOM to 200,000 ohm scale. Measure resistance between test pin 55 and test pins 40, 46, and 60. If resistance is less than 10,000 ohms, go to next step. If resistance is 10,000 ohms or greater, replace ECA and repeat QUICK TEST.
  9. Turn key OFF and wait 10 seconds. Leave breakout box connected and ECA and EHC solenoid disconnected. Set DVOM to 200,000 ohm scale. Measure resistance between test pin 55 and test pins 37 and 57. If resistance is 10,000 ohms or greater, replace ECA and repeat QUICK TEST. If resistance is less than 10,000 ohms, repair short to power and repeat QUICK TEST. If code is repeated, replace ECA.
Fig 1: EHC Circuit
G2577
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