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Test B1 - Vat Sensor

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
G120718
VANE AIR TEMPERATURE (VAT) SENSOR SPECIFICATIONS

Temperature: °F (°C) Volts Ohms
50 (10) 3.46 3770
68 (20) 3.07 2500
86 (30) 2.65 1700
104 (40) 2.23 1180
122 (50) 1.84 830
140 (60) 1.49 600
158 (70) 1.19 440
176 (80) 0.95 330
194 (90) 0.76 250
212 (100) 0.56 190
230 (110) 0.46 140
248 (120) 0.38 110
  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. Check For VREF at TPS. Turn key off and wait 10 seconds. Disconnect TPS. Set DVOM on 20-volt scale. Turn key on, leaving engine off. Measure voltage at TPS harness connector between VREF and SIG RTN. If reading is not 4-6 volts, go to TEST A3 - REF  . VOLTAGE, step 1). If voltage is 4-6 volts, connect TPS and go to next step.
  3. Checking VAT Sensor. Ensure ambient temperature is greater than 50°F. Turn key off and wait 10 seconds. Disconnect harness from vane meter. Set DVOM on 200K-ohm scale. Measure resistance at VAT sensor between VAT SIG and SIG RTN. See Fig 1 . If resistance is 125 ohms at 240°F (116°C) to 3700 ohms at 50°F (10°C), replace ECA. Connect vane meter and repeat QUICK TEST. If reading is out of range, remove vane meter. Spray carburetor cleaner on a clean cloth and pass cloth through meter to remove oil film buildup. DO NOT  spray inside vane meter. Reinstall vane meter. Repeat quick test. If code is still present, replace vane meter and repeat QUICK TEST.
  4. Code 54 or 58: Induce Opposite Code. 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 vane meter harness connector and ECA, a faulty vane meter, or a faulty ECA. Turn key off and wait 10 seconds. Disconnect harness from vane meter. Inspect and repair any damaged wiring. Install a jumper wire between VAT SIG and SIG RTN at vane meter harness connector. Perform KOEO SELF-TEST. If Code 64 or 68 is displayed, replace vane meter, remove jumper wire, reconnect vane meter, and repeat QUICK TEST. If code 64 or 68 is not displayed, remove jumper wire and go to next step.
  5. Checking Continuity of VAT Signal and Signal Return. Turn key off and wait 10 seconds. Disconnect vane meter and keep jumper wire removed. 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 vane meter harness connector. Also measure resistance between test pin No. 46 and SIG RTN at vane meter harness connector. If both readings are less than 5 ohms, replace ECA. Remove breakout box and connect wiring to ECA and vane meter. Repeat QUICK TEST. If either reading is 5 ohms or more, repair open circuit. Remove breakout box, connect wiring to ECA and vane 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 (Temperature is too High). Possible causes are, VAT signal output shorted to SIG RTN, ground, or VREF. A faulty vane meter or ECA. Turn key off and wait 10 seconds. Disconnect harness from vane meter. Inspect for and repair any damaged wiring. Perform KOEO SELF-TEST. If Code 54 or 58 is displayed, replace vane meter and reconnect 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. Disconnect TPS. Set DVOM on 20-volt scale. Turn key on, leaving engine off. Measure voltage between VREF and SIG RTN at TPS harness connector. If reading is not 4-6 volts, go to TEST A3 - REF  . VOLTAGE, step 1). If reading is 4-6 volts, connect TPS and go to next step.
  8. Checking VAT Signal For Shorts. Turn key off and wait 10 seconds. Disconnect vane meter. Disconnect ECA 60-pin connector. Inspect and repair as necessary. Install breakout box, with ECA disconnected. Set DVOM on 200K-ohm scale. Measure resistance between test pin No. 25 and test pins No. 40, 46, and 60 of breakout box. If any reading is less than 10K ohms, repair shorts in circuit(s). Remove breakout box, connect ECA and vane meter. Repeat QUICK TEST. If all readings are greater than 10K ohms, replace ECA. Remove breakout box and connect ECA. Repeat QUICK TEST.
  9. Continuous Code 54 or 58: VAT Sensor Check. 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 are, faulty harness or connectors, ECA or vane meter. Enter KOEO CONTINUOUS MONITOR (WIGGLE) TEST. Observe VOM or diagnostic tester for indication of fault while lightly tapping vane meter and then by wiggling connector. If fault is indicated, inspect connector and terminals and repair or replace as necessary. If connector and terminals are good, replace vane meter and repeat QUICK TEST. If a fault is not indicated, go to next step.
  10. EEC-IV Harness Check. While in CONTINUOUS MONITOR (WIGGLE) TEST, wiggle and bend EEC-IV harness from VAT sensor to instrument panel, a small section at a time. Also check harness from instrument panel 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. Checking ECA Harness and Connectors. 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 or replace 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 Memory Codes 64 or 68: VAT Sensor Check. A Code 64 or 68 indicates VAT signal was less than 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 vane meter and repeat QUICK TEST. If no fault is indicated, repeat steps 10) and 11).
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