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Circuit Test B1

NOTE: Perform this test only when service code 24, 28, 54, 58, 64, or 68 is received in QUICK TEST. 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.
Fig 1: VAT Sensor Circuit
G54772
VANE AIR TEMPERATURE (VAT) SENSOR SPECIFICATIONS

Temperature: °F (°C) Volts K Ohms
50 (10) 3.46 3.77
68 (20) 3.07 2.50
86 (30) 2.65 1.70
104 (40) 2.23 1.18
122 (50) 1.84 0.83
140 (60) 1.49 0.60
158 (70) 1.19 0.44
176 (80) 0.95 0.33
194 (90) 0.76 0.25
212 (100) 0.56 0.19
230 (110) 0.46 0.14
248 (120) 0.38 0.11
  1. Code 24 or 28: Check Ambient Temperature. Codes 24 and 28 indicate that the VAT sensor is out of Self-Test range. Correct range for measurement is .35-3.5 volts. Possible causes are; low ambient temperature, Faulty VAF meter, faulty ECA, faulty wiring or connector. Ensure ambient air temperature is at least 50°F (10°C). If not, repeat QUICK TEST. If temperature is at least 50°F (10°C), 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 harness connector between VREF and SIG RTN. If reading is less than 4 volts or more than 6 volts, go to CIRCUIT TEST A3 , step 1). If reading is between 4 and 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 and SIG RTN. If resistance is 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, repair or replace VAF meter and repeat QUICK TEST.
  4. Code 54 or 58: Induce Opposite Code. Service Code 54 and 58 indicate VAT sensor signal is greater than the Self-Test maximum of 3.5 volts (temperature is too low). Possible causes are a lack of continuity between the VAF harness connector and the ECA, a faulty VAF, or a faulty ECA. 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 SIG and SIG RTN at VAF meter connector. Perform KOEO SELF-TEST. If Code 64 or 68 is displayed, replace VAF meter. Remove jumper wire, connect airflow meter, and repeat QUICK TEST. If code 64 or 68 is not displayed, remove jumper wire and go to next step.
  5. Checking VAT Signal and Signal 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, at the breakout box and VAT SIG at VAF meter 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 more, repair open circuit. Remove breakout box, connect wiring to ECA and airflow meter. Repeat QUICK TEST.
  6. Code 64 or 68: Opposite Code Test. Service Code 64 or 68 indicates VAT sensor signal is less than Self-Test minimum value of 0.35 volts. Possible causes of this fault is, VAT signal shorted to signal return, ground, or VREF. A faulty VAF meter or a faulty ECA. Turn key off and wait 10 seconds. Disconnect harness from airflow meter. Inspect for and repair any damaged wiring. Perform KOEO SELF-TEST. If Code 54 or 58 is displayed, replace VAF meter and connect harness. Repeat QUICK TEST. If Code 54 or 58 is not displayed, go to next step.
  7. Checking VREF at TPS. 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 SIG RTN at connector. If reading is less than 4 volts or more than 6 volts, go to CIRCUIT TEST A3 , step 1). If reading is between 4 and 6 volts, connect TPS and go to next step.
  8. Checking VAT Signal For Shorts. 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 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 54 or 58. A Continuous Memory Code 54 or 58 indicates that the VAT signal was greater than the Self-Test maximum of 4.5 volts. The code was set during normal driving conditions. Possible causes for this fault: faulty harness or connectors, ECA or VAF meter. Enter KOEO 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 a fault is not 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 cowl, a small section at a time. Also check harness from cowl 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 ECA 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, clear codes and repeat QUICK TEST.
  12. Continuous Codes 64 or 68. A Code 64 or 68 indicates that the VAT signal was less than the Self-Test minimum of 0.3 volt. The code was set during normal driving conditions. Possible causes for this fault: faulty harness or connectors, ECA or VAF meter. Enter KOEO 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 VAF meter and repeat QUICK TEST. If no fault is indicated, go back and repeat steps 10) and 11).
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