Circuit Test D

Ambient air temperature must be at least 50°F (10°C) for test results to be valid. Avoid performing test in unusually hot or cold conditions.

1. Code 24 Displayed. Make sure ambient air temperature is at least 50°F (10°C). If not, repeat QUICK TEST  . If temperature is high enough, go to next step.
2. Turn key off and wait 10 seconds. Set DVOM on 20-volt scale. Disconnect Throttle Position Sensor (TPS). Turn key on, leaving engine off. Measure voltage at TPS connector between voltage reference (VREF) and signal return. If reading is less than 4.0 volts or higher than 6.0 volts, go to CIRCUIT TEST C  , step 1). If reading is between 4.0 and 6.0 volts, connect TPS and go to next step.
3. Turn key off and wait 10 seconds. Disconnect harness from airflow meter. Set DVOM on 200,000 ohm scale. Measure resistance at VAT sensor between VAT signal and signal return. If reading is from 125 ohms at 240°F (116°C) to 3700 ohms at 50°F (10°C), replace ECA. Connect airflow meter and repeat QUICK TEST  . If reading is out of range, replace airflow meter and repeat QUICK TEST  .
4. Code 54 Displayed. Turn key off and wait 10 seconds. Disconnect harness from airflow meter. Inspect for and repair any damaged wiring. Install a jumper wire between VAT signal and signal return at airflow meter connector. Perform KEY ON/ENGINE OFF SELF-TEST. If code 64 is displayed, replace airflow meter. Remove jumper wire, connect airflow meter, and repeat QUICK TEST  . If code 64 is not displayed, remove jumper wire and go to next step.
5. Turn key off and wait 10 seconds. With jumper wire removed, leave airflow meter disconnected. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Set DVOM on 200 ohm scale. Measure resistance between test pin No. 25 and VAT signal at connector. Also measure resistance between test pin No. 46 and signal return at connector. If both readings are less than 5 ohms, replace ECA. Remove breakout box and connect wiring to ECA and airflow meter. Repeat QUICK TEST  . If either reading is 5 ohms or higher, repair open circuit. Remove breakout box, connect wiring to ECA and airflow meter, then repeat QUICK TEST  .
6. Code 64 Displayed. Turn key off and wait 10 seconds. Disconnect harness from airflow meter. Inspect for and repair any damaged wiring. Perform KEY ON/ENGINE OFF SELF-TEST. If code 54 is displayed, replace airflow meter and connect harness. Repeat QUICK TEST  . If code 54 is not displayed, go to next step.
7. Turn key off and wait 10 seconds. Set DVOM on 20-volt scale. Disconnect TPS. Turn key on, leaving engine off. Measure voltage between VREF and signal return at connector. If reading is less than 4.0 volts or higher than 6.0 volts, go to CIRCUIT TEST C  , step 1). If reading is between 4.0 and 6.0 volts, connect TPS and go to next step.
8. Turn key off and wait 10 seconds. Leave airflow meter disconnected. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Set DVOM on 200,000 ohm scale. Measure resistance between test pin No. 25 and test pins No. 40, 46, and 60. If any reading is less than 10,000 ohms, repair shorts. Remove breakout box, connect ECA and airflow meter, then repeat QUICK TEST  . If all readings are 10,000 ohms or higher, replace ECA. Remove breakout box and connect ECA. Repeat QUICK TEST  .
9. Continuous Code 54 or 64 Displayed. Using CONTINUOUS MONITOR (WIGGLE) TEST  , observe VOM or STAR tester LED for indication of fault while tapping VAT sensor lightly and wiggling connector. If fault is indicated, inspect connector and terminals. If connector and terminals are good, replace VAT sensor and repeat QUICK TEST  . If no fault is indicated, go to next step.
10. While in CONTINUOUS MONITOR (WIGGLE) TEST  , wiggle and bend EEC-IV harness from VAT sensor to firewall, a small section at a time. Also check harness from firewall to ECA. If fault is indicated, isolate fault and repair as necessary. Repeat QUICK TEST  . If no fault is found, go to next step.
11. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect both connector and connector terminals for obvious damage. If connectors and terminals are not okay, repair as necessary and repeat QUICK TEST  . If connectors and terminals are okay, and you are unable to duplicate fault at this time, continuous code 54 or 64 testing is complete.

Fig 1: VAT Sensor Circuit