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Test G - Map/BP Sensor

NOTE: Barometric pressure sensor output is digital and must be measured with MAP/BP tester.

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: Unusually high/low atmospheric barometer reading. Kinked or blocked vacuum lines. Engine condition (valves, vacuum leaks, valve timing, EGR valve, etc.).

  1. Code 22 Displayed, Engine Off. Turn key off. Disconnect MAP/BP sensor from harness. Connect MAP/BP tester between wiring harness and MAP/BP sensor. Connect banana plugs of tester into DVOM and set DVOM on 20-volt scale. Go to next step.
    Fig 1: Correct Hookup For MAP/BP Tester
    G11077
  2. With MAP/BP tester connected, turn key on. If only Green light on tester is lit, VREF is correct. Go to step 4). If "less than 4 volts" Red light or no lights come on, VREF is too low. If "more than 6 volts" Red light comes on, VREF is too high. If VREF is too high or too low, go to next step.
  3. With MAP/BP tester connected, turn key on. Disconnect MAP/BP sensor and repeat step 2). If only Green light comes on, VREF is correct. Replace MAP/BP sensor and repeat QUICK TEST . If "less than 4 volts" Red light or no lights come on, VREF is too low. If "more than 6 volts" Red light comes on, VREF is too high. If VREF is too high or too low, remove MAP/BP tester, connect sensor, then go to TEST C - REFERENCE VOLTAGE , step 1).
  4. With MAP/BP tester connected and key on, measure sensor output voltage. If voltage output is in correct range for altitude of vehicle being tested, go to next step. If output reading is outside range, go to step 6).
    NOTE: Measure several known good MAP/BP sensors on available vehicles. Mean voltage reading will be typical for your location on date of testing.
    MAP VOLTAGE OUTPUT

    Elevation (Ft.) Voltage Output (Volts)
    0 1.55-1.63
    1000 1.52-1.60
    2000 1.49-1.57
    3000 1.46-1.54
    4000 1.43-1.51
    5000 1.40-1.48
    6000 1.37-1.45
    7000 1.35-1.43
    MAP SENSOR FREQUENCY

    Manifold Vacuum (In. Hg) Frequency (Hz) kPa
    0 159 0.00
    3 150 10.2
    6 141 20.3
    9 133 30.5
    12 125 40.6
    15 117 50.8
    18 (curb idle) 109 61.0
    21 (curb idle) 102 71.1
    24 95 81.3
    27 88 91.5
    30 80 101.6
  5. Turn key off and wait 10 seconds. Disconnect MAP/BP sensor from harness. 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 MAP/BP signal at sensor connector and test pin 45. If reading is less than 5 ohms, replace ECA. Connect ECA and MAP/BP sensor and repeat QUICK TEST . If reading is 5 ohms or higher, repair opens in wiring. Remove breakout box, connect ECA and MAP/BP sensor. Repeat QUICK TEST .
  6. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA disconnected. Disconnect harness at MAP/BP sensor. Set DVOM on 200,000-ohm scale. Measure resistance between test pin 45 and test pins 26, 46, 40, and 60. If any reading is less than 10,000 ohms, repair shorts in wiring. Remove breakout box and connect ECA and MAP/BP sensor. Repeat QUICK TEST . If all readings are 10,000 ohms or higher, replace MAP/BP sensor. Remove breakout box and connect all wiring. Repeat QUICK TEST .
  7. Code 22 Displayed, Engine Running. Turn key off and wait 10 seconds. Disconnect vacuum line from MAP sensor. Hook vacuum pump to MAP sensor and apply 18 in. Hg. vacuum to sensor. If sensor does not hold vacuum, replace MAP sensor, connect vacuum line and repeat QUICK TEST . If MAP sensor does hold vacuum, go to next step.
  8. Turn key off and wait 10 seconds. Plug vacuum supply hose to MAP sensor. Start engine and hold in 1400-1600 RPM range. Slowly apply 15 in. Hg vacuum to MAP sensor. Perform ENGINE RUNNING SELF-TEST while holding RPM range. Ignore all other codes at this time. If code 22 is still displayed, replace MAP sensor. Connect vacuum hose and repeat QUICK TEST . If code 22 is not displayed, check vacuum hose to sensor and repair. If hose is good, service other codes as necessary, then check engine for low vacuum condition.
  9. Turn key off and wait 20 seconds. Plug vacuum supply hose to MAP sensor. Start engine and hold in 1400-1600 RPM range. Slowly apply 15 in. HG vacuum to MAP sensor. Perform ENGINE RUNNING SELF-TEST while holding RPM range. Ignore all other codes at this time. If code 22 is still displayed, replace MAP sensor. Connect vacuum hose and repeat QUICK TEST . If code 22 is not displayed, check vacuum hose to sensor and repair. If hose is good, service other codes as necessary. Check engine for low vacuum condition.
  10. Code 72 Displayed. Turn key off and wait 10 seconds. Install vacuum gauge with "T" in manifold vacuum line at MAP sensor. Perform ENGINE RUNNING SELF-TEST and observe vacuum reading before and during DYNAMIC RESPONSE CHECK portion of test. Record service codes. If vacuum decreased 10 in. Hg or more and code 72 is not displayed, disconnect vacuum gauge and service other codes as necessary. If vacuum decreased 10 in. Hg and code 72 is displayed, replace MAP sensor and repeat QUICK TEST . If vacuum decreased less than 10 in. Hg, go to next step.
  11. Check vacuum lines for correct routing, using vehicle emissions decal as a guide. Also check MAP sensor vacuum lines for kinks or blockage. If lines are good, EEC-IV system is okay. Check engine for cause of low vacuum. If vacuum lines are bad, repair as necessary and repeat step 10).
  12. Turn key off. Disconnect MAP/BP sensor from harness. Connect MAP/BP tester between wiring harness and MAP/BP sensor. Connect banana plugs of tester into DVOM and set DVOM on 20-volt scale. Go to next step.
  13. Turn key on and measure sensor output. Compare values to MAP VOLTAGE OUTPUT  table. If reading is out of range, replace MAP/BP sensor. Repeat QUICK TEST . If reading is within range, go to next step.
  14. Check MAP sensor vacuum lines for leaks, bad connections, kinks or blockage. If vacuum lines are okay, go to DIAGNOSIS BY SYMPTOM TEST . If vacuum lines are bad, repair as necessary and repeat QUICK TEST .
  15. CONTINUOUS Code 22 Displayed. Using CONTINUOUS MONITOR (WIGGLE) TEST , observe VOM or STAR tester LED for indication of fault while doing the following: connect vacuum pump to MAP sensor and slowly apply 25 in. Hg. Bleed vacuum slowly, tap MAP sensor lightly, and wiggle MAP connector. If fault is indicated, disconnect sensor. Inspect connector and terminals for damage. If connector and terminals are okay, replace MAP sensor and repeat QUICK TEST . If no fault is indicated, go to next step.
  16. Stay in CONTINUOUS MONITOR (WIGGLE) TEST . Observe VOM or STAR tester LED for indication of fault while shaking, bending or wiggling small sections of harness from sensor connector to firewall. Check harness from firewall to ECA in same manner. If fault is indicated, isolate fault in harness and repair as necessary. Repeat QUICK TEST . If no fault is indicated, go to next step.
  17. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect both connector and terminals for obvious damage. If connector and terminals are damaged, repair as necessary. Repeat QUICK TEST . If connector and terminals are okay, fault cannot be duplicated at this time. Continuous code 22 testing is complete.
Fig 2: MAP/BP Sensor Circuit
G11078
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