Test B1 - Vane Air Temperature (Vat) Sensor

Fig 1: VAT Sensor Circuit

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 28: Check Ambient Temperature  - Ensure ambient air temperature is at least 50°F (10°C). If not, repeat QUICK TEST  . If temperature is hot enough, go to next step.
2. Voltage Reference at TPS  - 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 volts or more than 6 volts, go to TEST A3  , step 1). If reading is between 4-6 volts, connect TPS and go to next step.
3. Checking VAT Sensor  - Turn key off and wait 10 seconds. Disconnect harness from airflow meter. Set DVOM on 200K-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 58: Testing Airflow Meter  - 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 (KOEO) SELF-TEST  . If code 68 is displayed, replace airflow meter. Remove jumper wire, connect airflow meter, and repeat QUICK TEST  . If code 68 is not displayed, remove jumper wire and go to next step.
5. Checking VAT Signal and Return  - 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 (No. 43 on 2.3L Turbo MPFI), at the breakout box and VAT signal at connector. Also, measure resistance between Test Pin No. 46 and signal return at the connector. If both readings are less than 5 ohms, replace ECA. Remove breakout box. Connect wiring to ECA and airflow meter. Repeat QUICK TEST  . If either reading is 5 ohms or more, repair open circuit. Remove breakout box, connect wiring to the ECA and airflow meter. Repeat QUICK TEST.
6. Code 68: Opposite Code Test  - Turn key off and wait 10 seconds. Disconnect harness from airflow meter. Inspect for and repair any damaged wiring. Perform KEY ON/ENGINE OFF (KOEO) SELF-TEST  . If code 58 is displayed, replace airflow meter and connect harness. Repeat QUICK TEST  . If code 58 is not displayed, go to next step.
7. Checking VREF at TPS  - Turn key off. 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 volts or more than 6 volts, go to TEST A3  , step 1). If reading is between 4-6 volts, connect TPS and go to next step.
8. Checking For Shorts at VAT Signal  - 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 200K-ohm scale. Measure resistance between Test Pin No. 25 (No. 43 on 2.3L Turbo MPFI engine) and Test Pins No. 40, 46, and 60. If any reading is less than 10K ohms, repair shorts. Remove breakout box, connect ECA and airflow meter. Repeat QUICK TEST  . If all readings are 10K ohms or more, replace ECA. Remove breakout box and connect ECA. Repeat QUICK TEST.
9. Continuous Code 58 or 68 Displayed  - Using CONTINUOUS MONITOR (WIGGLE) TEST  , observe VOM or diagnostic tester 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. Wiggle Testing Harness  - 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. Inspecting Connectors and Terminals  - 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 damaged, 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 58 or 68 testing is complete.