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Circuit Test B9

NOTE: Perform this test when Service Code 26, 56, 66, or 76 is displayed during QUICK TESTS or when directed here by other test procedures.
Fig 1: VAF Sensor Circuit
G54780

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: check for air leaks between VAF sensor and throttle body. Check for vacuum leaks. Check engine sealing at PCV, CANP, valve cover(s), and at dipstick seal.

  1. Code 26: VAF Movement Obstructed. Code 26 indicates VAF sensor signal is out of Self-Test range. Self-Test range is 0.17-0.50 volts with KOEO or 1.10-1.70 volts with KOER. Possible causes for this fault are a faulty vane meter, faulty ECA or wiring harness. Turn key off and wait 10 seconds. Remove air filter and check for contamination (oil residue or foreign matter). If Code 26 appears in KOEO SELF-TEST, replace or service VAF sensor. Install air cleaner and repeat QUICK TEST. If Code 26 is not displayed, go to next step.
  2. Checking VAF Sensor. With key off, check for air leaks allowing unmetered air into system between VAF sensor and throttle body. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box and connect ECA to box. Set DVOM on 20-volt scale. Turn key on, leaving engine off. Place new, unsharpened pencil through air inlet opening of VAF sensor. See VAF SENSOR CHECK illustration. Measure voltage between test pins No. 43 and 46. If reading is between 2.8 and 3.7 volts, VAF sensor is okay. Code 26 may be caused by incorrect engine speed or vacuum leak. Go to CIRCUIT TEST D4 , step 11) and ensure Code 26 has not been caused by canister purge function. Repair problem, remove breakout box and repeat QUICK TEST. If reading is not between 2.8 and 3.7 volts, inspect VAF connector pins and repeat QUICK TEST. Replace VAF if problem still exists.
    Fig 2: VAF Sensor Check
    G54781
  3. Code 56: Generate Code 66. Code 56 indicates that the VAF signal is greater than the Self-Test maximum of 4.89 volts. Possible causes for this fault are a faulty VAF, faulty ECA, VAF SIG circuit shorted to power or a faulty wiring harness. Turn key off and wait 10 seconds. Disconnect harness from VAF. Inspect for and repair any damaged wiring. Rerun KOEO SELF-TEST. If Code 66 is not displayed, go to step 5). If Code 66 is displayed, go to next step.
  4. Checking VAF Signal Return Voltage. Turn key off and wait 10 seconds. Leave harness disconnected from VAF sensor. Set DVOM on 20-volt scale. With KOEO measure voltage at VAF harness connector between VREF and SIG RTN. If reading is between 4 and 6 volts, replace VAF sensor. Connect harness and repeat QUICK TEST. If reading is less than 4 or more than 6 volts, go to CIRCUIT TEST A3 , step 1).
  5. Checking VAF Signal For Shorts to Power. Turn key off and wait 10 seconds. Leave VAF sensor disconnected. Disconnect 60-pin connector from ECA. 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. 43 and test pins No. 26 and 57. If either reading is less than 10K ohms, repair short in wiring. Remove breakout box. Connect ECA and VAF sensor and then repeat QUICK TEST. If both readings are 10K ohms or more, replace ECA. Remove breakout box. Connect ECA and VAF sensor. Repeat QUICK TEST.
  6. KOEO Code 66: Generate Code 56. Code 66 indicates that the VAF signal is less than the Self-Test minimum of 0.17 volt during the KOEO SELF-TEST. Possible causes for this fault are a faulty VAF, faulty ECA, VAF SIG circuit shorted to ground or a faulty wiring harness. Turn key off and wait 10 seconds. Disconnect harness from VAF sensor. Install jumper wire between VREF and VAF SIG at connector. Perform KOEO SELF-TEST. Ignore all codes except VAF codes at this time. If no codes are displayed, immediately remove jumper wire and go directly to step 9). If Code 56 is displayed, replace VAF sensor. Remove jumper wire, connect VAF sensor, and repeat QUICK TEST. If Code 56 is not displayed, remove jumper wire and go to next step.
  7. Checking VREF at VAF Sensor. Turn key off and wait 10 seconds. Leave VAF sensor disconnected. Turn key on, leaving engine off. Set DVOM on 20-volt scale. Measure voltage between VREF and SIG RTN return at VAF sensor harness 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, go to next step.
  8. Checking Continuity of VAF SIG. With key off and VAF sensor 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 VAF SIG at sensor connector and test pin No. 43. If reading is 5 ohms or more, repair open circuit. Remove breakout box, connect ECA and VAF sensor. Repeat QUICK TEST. If reading is less than 5 ohms, go to next step.
  9. Checking VAF Signal For Short to Ground. Turn key off and wait 10 seconds. Leave ECA and VAF sensor disconnected. Set DVOM on 200K-ohm scale. Measure resistance between VAF SIG and SIG RTN at harness connector. Also measure resistance between VAF SIG and negative battery terminal. If either reading is less than 10K ohms, repair shorts. Connect VAF sensor and repeat QUICK TEST. If both readings are 10K ohms or more, replace ECA. Remove breakout box, and connect ECA and VAF sensor. Repeat QUICK TEST.
    NOTE: A quick "Goose" test may not be sufficient to pass step 10). Be sure to move throttle to WOT. For additional information, see KOER SELF-TEST, DYNAMIC RESPONSE CHECK in front of this article.
  10. KOER Code 76 Displayed. Code 76 indicates that VAF output voltage did not change during the WOT "Goose" test. Possible causes for this fault are an obstructed air cleaner or duct, a faulty vane meter or a faulty ECA. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box and connect ECA. Set DVOM on 20-volt scale. Connect DVOM to test pin No. 43 and 46. Perform KOER SELF-TEST while observing DVOM. As soon as DYNAMIC RESPONSE CHECK signal is displayed, perform WOT. Reading on DVOM should increase by more than 2 volts from the reading before WOT. Observe service codes at end of test. If reading increased by more than 2 volts, go to next step. If not, check air cleaner duct for obstructions. If okay, replace VAF sensor.
  11. Checking Service Codes. Observe KOEO SELF-TEST service codes at end of step 10). If Code 76 is still displayed, replace ECA. Remove breakout box and repeat QUICK TEST. If Code 76 is not displayed, VAF sensor is okay. Service other codes as necessary.
  12. Continuous Memory Code 56. Code 56 indicates that the VAF sensor signal was greater than the Self-Test maximum value of 4.89 volts. The code was set during normal driving conditions. Possible causes for this fault are a faulty vane meter, Using KOEO CONTINUOUS MONITOR (WIGGLE) TEST, observe VOM or diagnostic tester for indication of fault while lightly tapping VAF sensor and wiggling connector. If a fault is indicated, disconnect connector. Inspect connector and terminals for damage. If connector and terminals are okay, replace VAF sensor and repeat QUICK TEST. If no fault is indicated, go to next step.
  13. Checking Harness. While in KOEO CONTINUOUS MONITOR (WIGGLE) TEST, shake, bend and wiggle small sections of EEC-IV harness from VAF sensor connector to firewall and from firewall to ECA. If fault is indicated, isolate and repair damaged wiring. Repeat QUICK TEST. If no fault is indicated, go to next step.
  14. Checking Harness Connectors. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect both connectors and terminals for obvious damage. If connectors and terminals are damaged, repair as necessary and repeat QUICK TEST. If connectors and terminals are okay, fault cannot be duplicated at this time. Clear codes and rerun QUICK TEST.
  15. KOER Code 66. KOER Code 66 indicates that the VAF sensor signal was less than the Self-Test minimum of 0.17 volts. The code was set during normal driving conditions. Possible causes for this fault are a faulty VAF harness or connector, faulty VAF sensor, or a fault ECA. Enter KOEO Continuous Monitor mode. Observe DVOM while tapping lightly on VAF sensor to simulate road shock. Wiggle VAF connector. If a fault is indicated repair wiring or connectors as necessary. If connectors and wiring are okay, replace VAF sensor. If a fault is not indicated, check harness and connectors as described in steps 13) and 14).
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