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Diagnostic Aids

WARNING: This page is about a different car, the 1995 Lincoln Mark VIII. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test when instructed during QUICK TEST or if directed by other test procedures. To prevent replacement of good components, be aware the following non-EEC related areas may be at fault:

This test is only intended to diagnose:

  1. Check For Idle Air Codes

    Code 121 indicates TP sensor is inconsistent with MAF value. Code 124 indicates TP sensor value is higher than expected. Code 125 indicates TP sensor value is lower than expected. Turn ignition on. Repeat KOEO SELF-TEST  . If Code 411 or 412 is present, perform appropriate circuit test. See DIAGNOSTIC TROUBLE CODE REFERENCE CHARTS  . If Code 411 or 412 is not present, go to next step.

  2. Throttle Position (TP) Sensor: TP Sensor Integrity

    Turn ignition off. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV). Connect PCM to breakout box. Connect DVOM to test pins No. 46 and 47 at breakout box. Turn ignition on. Slowly apply throttle to WOT, and release to closed position. Voltage should change smoothly from 0.4-4.5 volts. See CIRCUIT TEST DH  for schematics and TP sensor specifications. If voltage change is incorrect or erratic, ensure TP sensor is properly installed. If TP sensor is properly installed, replace TP sensor. Remove breakout box, reconnect all components, and repeat QUICK TEST  . If voltage is okay and Code 121 is present, go to step 8). If voltage is okay and Code 121 is not present, go to next step.

  3. Check Idle

    Ensure idle is correct. If idle is correct, go to next step. If idle is incorrect, see IDLE SPEED in the ADJUSTMENTS article.

  4. Check Throttle Body

    Ensure idle is correct. Check throttle and/or cruise control linkage for binding and rough operation. Inspect throttle body for sludge build-up. Check engine vacuum hoses. Refer to Vehicle Emission Control Information (VECI) decal for proper vacuum hose routing. Check for air leak between IAC solenoid and MAF sensor. If problems are found, repair as necessary. Remove breakout box, reconnect all components, and repeat QUICK TEST  . If no problems are found, go to next step.

  5. Check MAP/BARO Sensor Output

    On vehicles without MAP/BARO go to next step. On vehicles with MAP/BARO, see DIAGNOSTIC AIDS  , then continue with this test. With tester connected and ignition on, measure sensor output voltage. If output voltage is within range for specified altitude, remove MAP/BARO tester and go to next step. See MAP SENSOR VOLTAGE OUTPUT  table for specification. If output voltage is not within range, replace MAP/BARO sensor. Remove breakout box, reconnect all components, and repeat QUICK TEST  .
    MAP SENSOR VOLTAGE OUTPUT

    Elevation (Feet) 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

  6. Check IAT Sensor

    Ensure ambient temperature is more than 50°F (10°C) before performing this test. Also, check and repair any air leaks in front of IAT sensor. Turn ignition off. Connect breakout box to PCM. Set DVOM to 20-volt scale. Connect DVOM to test pins No. 25 and 46. Start engine, and let it idle. Observe voltage as engine warms up. See CIRCUIT TEST DA  for voltage specifications. If voltage decreases smoothly and stabilizes when engine reaches operating conditions, system is operating properly at this time. Testing is complete. If voltage does not decrease smoothly and stabilize after engine reaches operating conditions, replace IAT sensor and repeat QUICK TEST  .

  7. Continuous Memory Code 184 & 185: Inspect MAF Sensor

    Code 184 indicates MAF sensor signal is higher than expected. Code 185 indicates MAF sensor signal is lower than expected. Turn ignition off. Check for air leaks between Idle Air Control (IAC) solenoid and MAF sensor. Inspect MAF sensor for oil contamination caused by excessive blow-by or malfunctioning PCV. If problems are found, repair as necessary. Clear codes and repeat QUICK TEST  . If no problems are found, go to step 10).

  8. Check MAF Sensor Circuit Voltage

    Turn ignition off. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV). Connect PCM to breakout box. Start engine, and warm it to normal operating temperature. Measure voltage between test pin No. 50 and test pin No. 40 or 60 at breakout box. If voltage is not within specification, replace MAF sensor. Remove breakout box, reconnect all components, and repeat QUICK TEST  . For MAF sensor specifications, see the appropriate PIN VOLTAGE CHARTS article. If voltage is within acceptable range, system is operating normally at this time. Sometime during the last 80 warm-up cycles, MAF sensor signal was out of range.

  9. Continuous Memory Code 186 & 187: Visual Vacuum Checks

    Code 186 indicates pulse width is longer than expected (rich). Code 187 indicates pulse width is shorter than expected (lean). Inspect air cleaner and air inlet duct. Replace or repair an necessary. Check for unmetered air leaks between MAF sensor and IAC solenoid. Check all engine vacuum hoses for damage, blockage and improper routing. Repair a necessary, and repeat QUICK TEST  . If all checks are okay, go to next step.

  10. Check Fuel Pressure

    Turn ignition off. Install fuel pressure gauge. Ensure vacuum hose is connected to fuel pressure regulator (if applicable). Start engine, and run it at idle. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, repair as necessary. See FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

  11. Verify Fuel Pressure Retention Ability

    Turn ignition on. If fuel pressure remains at specification for 60 seconds, go to next step. If fuel pressure does not remain at specification, repair fuel delivery system as necessary. See FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article.

  12. Cylinder Balance Test

    Perform KOER SELF-TEST  . After last code, wait 5-10 seconds, and then goose throttle lightly (not wide open throttle). This will activate cylinder balance test. If Code 90 is present after test, go back to step 7). If Code 90 is not present after test, go to CIRCUIT TEST H  , step 4).


If possible, measure several known good MAP/BARO sensors. Average voltage reading will be typical for location and day of testing. Also, refer to CIRCUIT TEST DF  for MAP/BARO sensor output check. See Figure for connector terminal identification and MAP/BARO tester hookup.

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