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Diagnostic Trouble Codes - 1991
Ford

 111  System "pass"
 112  ACT sensor circuit grounded.
 113  ACT sensor circuit open.
 114  ACT sensor is out of Self-Test.
 116  ECT sensor is out of Self-Test.
 117  ECT sensor circuit grounded.
 118  ECT sensor circuit open.
 121  TP sensor is out of Self-Test.
 122  TP sensor input is less than Self-Test minimum.
 123  TP sensor input is greater than Self-Test maximum.
 124  TP sensor input voltage is greater than expected.
 125  TP sensor input voltage is less than expected.
 129  Insufficient MAF input.
 136  HEGO sensor circuit indicates system lean (Right HEGO).
 137  HEGO sensor circuit indicates system rich (Right HEGO).
 139  No HEGO switching (Front Side).
 144  No HEGO switching (Left Side).
 157  MAF sensor circuit open.
 158  MAF sensor shorted to power.
 159  MAF sensor is out of Self-Test.
 167  Insufficient TP input change.
 171  Lack of HEGO switching (Rear Side).
 172  HEGO sensor circuit indicates lean. (Rear Side).
 173  HEGO sensor circuit indicates rich. (Rear Side).
 175  Lack of HEGO switching (Front Side).
 176  HEGO sensor circuit indicates lean. (Front Side).
 177  HEGO sensor circuit indicates rich. (Front Side).
 179  Fuel system at part throttle lean adaptive limit, system rich (Rear Side).
 181  Fuel system at part throttle rich adaptive limit, system lean (Rear Side).
 182  Fuel system at idle lean adaptive limit, system rich (Rear Side).
 183  Fuel system at idle rich adaptive limit, system lean (Rear Side).
 184  MAF sensor input voltage is greater than expected, in range.
 185  MAF sensor input voltage is less than expected, in range.
 186  Closed loop injector pulse width longer than expected.
 187  Closed loop injector pulse width shorter than expected.
 188  Fuel system at part throttle lean adaptive limit, system rich (Front Side).
 189  Fuel system at part throttle rich adaptive limit, system lean (Front Side).
 191  Fuel system at idle lean adaptive limit, system rich (Front Side).
 192  Fuel system at idle rich adaptive limit, system lean (Front Side).
 211  PIP circuit failure.
 212  Loss of tachometer/IDM input.
 213  EEC SPOUT circuit open.
 214  CID circuit failure.
 326  PFE sensor circuit voltage lower than expected.
 327  PFE sensor circuit voltage below Self-Test minimum.
 332  Insufficient EGR flow.
 335  PFE sensor circuit voltage out of Self-Test range.
 336  PFE sensor circuit voltage higher than expected.
 337  PFE sensor circuit voltage above Self-Test maximum.
 411  Cannot control RPM during KOER low RPM check.
 412  Cannot control RPM during KOER high RPM check.
 452  Insufficient input from VSS.
 511  ROM test failure.
 512  KAM test failure.
 513  EEC internal voltage failure.
 519  PSPS circuit open.
 521  PSPS circuit did not change.
 522  Vehicle not in PARK or NEUTRAL during KOEO.
 536  Brake On/Off circuit failure/not activated during KOER.
 538  Insufficient RPM change during KOER Dynamic Response Test.
 542  Fuel pump circuit open, EEC processor to motor ground.
 543  Fuel pump circuit open, battery to EEC processor.
 556  Fuel pump circuit failure.
 558  Electronic Vacuum regulator circuit failure.
 563  High speed Electro Drive Fan circuit failure.
 564  Electro Drive Fan circuit failure.
 565  Canister purge (CANP) circuit failure.
 621  Shift solenoid #1 circuit failure.
 622  Shift solenoid #2 circuit failure.
 624  EPC solenoid or driver failure.
 625  EPC solenoid driver open in EEC processor.
 628  Lock-up solenoid circuit failure, excessive clutch slippage.
 629  Lock-up solenoid circuit failure.
 634  MLP sensor voltage out of Self-Test range.
 636  Transmission oil temperature sensor voltage out of Self-Test range.
 637  Transmission oil temperature sensor voltage above Self-Test maximum.
 638  Transmission oil temperature sensor voltage below Self-Test minimum.
 639  Insufficient input from turbine speed sensor.
 641  Shift solenoid #3 circuit failure.
 645  Incorrect gear ratio obtained for first gear.
 646  Incorrect gear ratio obtained for second gear.
 647  Incorrect gear ratio obtained for third gear.
 648  Incorrect gear ratio obtained for fourth gear.
 649  EPC range failure.
 651  EPC circuit failure.
 998  Hard faults present.

To extract DTCs from the computer for diagnostic purposes, the Self Test connector is used.

  1. Start engine and bring to normal operating temperature. If engine will not start or stalls after starting, proceed with next step.
  2. Turn the key "OFF", then wait ten seconds.
  3. Activate the self test by grounding the Self-Test Input (STI) connector.
  4. Turn the ignition key "ON".
  5. Record all codes received.
  6. Turn ignition "OFF".


Data Link Connector (DLC)
(Located Underhood)


Analog Voltmeter Connection

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