Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. See HOW TO USE CIRCUIT TESTS under CIRCUIT TESTS before performing this test. Fuel-contaminated engine oil may affect Codes 41/172, 91/136, 42/173 and 92/137. If fuel-contaminated engine oil is suspected, remove PCV valve from valve cover and repeat QUICK TEST . If problem is corrected, change engine oil and filter. Only use this test to diagnose:

HEGO sensor.
HEGO signal, ground circuit and sensor connection.
Vacuum systems.
Fuel injector and/or fuel injector circuitry.
ECA.
Electrical circuits (HEGO GND, HEGO, INJ 1-8, VPWR and SIG RTN).

To prevent replacement of good components, be aware following non-EEC areas may be cause of driveability concerns:

Ignition system.
Faulty evaporative emission system.
EGR system.
Air intake system.
Engine oil contamination.
Fuel system.
Intake or exhaust system leaks.
Engine cooling system.

CIRCUIT TEST H DTC

Service Code	HEGO Sensor Orientation	Fault Definition
41/172r 91/136r 176c	Right or Rear Left or Front Left or Front	HEGO Lean, Lack Of Switching
42/173r 92/137r 177c	Right or Rear Left or Front Left or Front	HEGO Rich, Lack Of Switching
144/41c 139/91c	Right or Rear Left or Front	No HEGO Switch Detected
171c 175c	Right or Rear Left or Front	Adaptive Fuel Limit Reached, Lack Of HEGO Switching
174c 178c	Right or Rear Left or Front	Lazy HEGO, Slow To Switch

INDIVIDUAL INJECTOR RESISTANCE

Engine	Ohms
2.3L OHC & 3.0L	15.0-18.0
All Other Engines	13.0-16.0

INJECTOR BANK RESISTANCE

Engine	Ohms
2.3L HSC	6.0-8.0
2.3L OHC	7.0-9.5
2.9L, 3.0L & 4.9L	5.0-6.5
5.0L, 5.8L	3.0-4.0

Fig 1: Test Schematic (1.9L)

Fig 2: Test Schematic (2.3L HSC)

Fig 3: Test Schematic (2.3L OHC)

Fig 4: Test Schematic (Probe 3.0L)

Fig 5: Test Schematic (Taurus 3.0L SHO)

Fig 6: Test Schematic (3.0L Except Probe & Taurus SHO; 3.8L)

TEST PIN NO. 12 WIRE COLOR IDENTIFICATION

Application	Wire Color
Cougar & Thunderbird	Light Green
Except Cougar & Thunderbird	Light Green/Orange

TEST PIN NO. 15 WIRE COLOR IDENTIFICATION

Application	Wire Color
Cougar & Thunderbird	Tan/Light Blue
Except Cougar & Thunderbird	Tan/Black

TEST PIN NO. 43 WIRE COLOR IDENTIFICATION

Application	Wire Color
Cougar & Thunderbird	Tan/Red
Except Cougar & Thunderbird	Red/Black

TEST PIN NO. 44 WIRE COLOR IDENTIFICATION

Application	Wire Color
Cougar & Thunderbird	Tan/Orange
Sable & Taurus	Dark Blue/Light Green
Except Cougar, Sable, Taurus & Thunderbird	Gray/Light Blue

TEST PIN NO. 46 WIRE COLOR IDENTIFICATION

Application	Wire Color
Cougar & Thunderbird	Black/White
Except Cougar & Thunderbird	Green/Red

Fig 7: Test Schematic (4.6L; Cougar & Thunderbird - 5.0L)

TEST PIN NO. 12 WIRE COLOR IDENTIFICATION

Application	Wire Color
4.6L	Light Green/Orange
5.0L	Light Green

TEST PIN NO. 13 WIRE COLOR IDENTIFICATION

Application	Wire Color
4.6L	Tan/Red
5.0L	Tan/Orange

TEST PIN NO. 15 WIRE COLOR IDENTIFICATION

Application	Wire Color
4.6L	Tan
5.0L	Tan/Light Blue

TEST PIN NO. 43 WIRE COLOR IDENTIFICATION

Application	Wire Color
4.6L	Red/Black
5.0L	Tan/Red

TEST PIN NO. 44 WIRE COLOR IDENTIFICATION

Application	Wire Color
4.6L	Gray/Light Blue
5.0L	Tan/Orange

TEST PIN NO. 46 WIRE COLOR IDENTIFICATION

Application	Wire Color
4.6L	Gray/Red
5.0L	Black/White

Fig 8: Test Schematic (Mark VII 5.0L & Mustang 5.0L)

TEST PIN NO. 29 WIRE COLOR IDENTIFICATION

Application	Wire Color
Mark VII	Red/Black
Mustang	Gray/Light Blue

TEST PIN NO. 43 WIRE COLOR IDENTIFICATION

Application	Wire Color
Mark VII	Dark Blue/Light Green
Mustang	Red/Black

CIRCUIT TEST H ACRONYMS

Acronym	Definition
HEGO	Heated Exhaust Gas Oxygen Sensor
SEFI	Sequential Electronic Fuel Injection

1) Check For Contaminated Engine Oil Turn ignition off. Remove PCV valve from valve cover. Inspect PCV system for damage. Inspect valve for blockage and movement of valve plunger. Repair as necessary. Perform KOER SELF-TEST . If vehicle is a no-start, KOER Code 41/172, 42/173, 91/136 or 92/137 or Continuous Memory Code 41/144, 91/139, or 172 is present, install PCV valve and go to step 2). If no codes are set, change engine oil and filter. Install PCV valve, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST .

2) Check Fuel Pressure Turn ignition off. Install fuel pressure gauge. Ensure manifold vacuum supply is connected to fuel pressure regulator (if equipped). Run engine at idle and check fuel pressure. If vehicle will not start, cycle ignition on and off several times. Check fuel pressure. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is within specification, go to step 3). If pressure is not within specification, go to FUEL SYSTEM in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

3) Check System Ability To Hold Fuel Pressure Turn ignition on. If fuel pressure remains at specification for 60 seconds, go to step 4) (no-starts), step 5) (non-SEFI) or step 6) (SEFI). If fuel pressure is not as described, repair fuel delivery system as necessary.

4) Fuel Delivery Test Release fuel system pressure. Install fuel pressure gauge, and pressurize fuel system as in step 1). Disconnect inertia switch. Crank engine 5 seconds. If fuel pressure drop is greater than 5 psi after 5 seconds of cranking, EEC-IV system is not causing no-start condition. Check additional no-start tests in TESTS W/O CODES article in the ENGINE PERFORMANCE Section. If fuel pressure drop is less than 5 psi, remove fuel pressure gauge. Connect inertia switch. Go to step 7) for non-SEFI or step 8) for SEFI.

5) Cylinder Balance Test (Non-SEFI) Connect a tachometer to engine. Start engine, and run it at idle. Disconnect and reconnect injectors individually, noting RPM drop as each injector is disconnected. ISC motor will attempt to re-establish RPM. If each injector does not produce a momentary drop in RPM, go to step 7). If each injector produces a momentary drop in RPM, go to step 13) for Codes 41/172, 91/136 or 176, step 24) for Codes 42/173, 92/137 or 177 or step 14) for all others.

6) Cylinder Balance Test (SEFI) Perform KOER SELF-TEST . After last code is displayed, wait 5-10 seconds. Enter CYLINDER BALANCE TEST by lightly goosing throttle (not WOT). Test time is about 2-3 minutes. To interpret codes retrieved from test, refer to CYLINDER BALANCE TEST SERVICE CODES . If no fault codes are present, go to step 8). If a Cylinder Balance Test service code is not displayed, fuel delivery is okay; fault is in area common to all cylinders. Code 77/538 indicates throttle was touched when test was ran and test is not completed. Code 538 could also be output if Continuous Memory Code 214 (CID) is present. If Continuous Memory Code 214 is present, see appropriate chart under SERVICE CODE REFERENCE CHARTS for instruction. For symptoms or Code 41/172, 91/136 or 176, go to step 13). For Code 42/173, 92/137 or 177, go to step 24). For all other codes, go to step 14).

CYLINDER BALANCE TEST SERVICE CODES

Service Code	Application
90	Pass
10	Cylinder No. 1
20	Cylinder No. 2
30	Cylinder No. 3
40	Cylinder No. 4
50	Cylinder No. 5
60	Cylinder No. 6
70	Cylinder No. 7
80	Cylinder No. 8
77/538	Retest

7) Check Injector & Harness Resistance (Non-SEFI) Turn ignition off. Wait 10 seconds. Disconnect ECA 60-pin connector. Inspect pins for damage. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance of injector banks between test pins No. 37 and 58 at breakout box. Measure resistance of injector banks between test pins No. 37 and 59 at breakout box. Record resistances. Refer to INJECTOR BANK RESISTANCE in this circuit test. If each resistance is within specifications, go to step 12). If resistance is not as specified, repair open circuit on VPWR circuit for no-start or go to step 9) for all other conditions.

8) Check Injector & Harness Resistance (SEFI) Turn ignition off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect pins for damage. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure and record resistance between suspected injector circuit test pin and test pin No. 37. For no starts, measure and record resistance between any injector circuit test pin and test pin No. 37. Refer to INJECTOR BANK RESISTANCE in this circuit test. If each resistance is within specification, go to step 12). If resistance is not as specified, repair open circuit on VPWR circuit for no-start or go to step 9 for all other conditions.

9) Check Continuity Of Fuel Injector Harness Turn ignition off. Disconnect injector wiring harness connector at injectors. Set DVOM to 200-ohm scale. Measure resistance between test pins No. 37 and 57 at breakout box and each injector VPWR terminal at wiring harness connector. See Fig 1 -Fig 6 . Measure resistance between injector test pin(s) at breakout box and same injector circuit terminal at each injector wiring harness connector. If each resistance is less than 5 ohms, go to step 10). If each resistance is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST .

10) Check Injector Harness Ckt. For Short To Power Or Ground Turn ignition off, and wait for 10 seconds. With breakout box installed and ECA disconnected, disconnect fuel injector vehicle harness. See Fig 1 . Set DVOM to 200-k/ohm scale. Measure resistance between injector test pin(s) and test pins No. 37, 40, 46, 57 and 60. Measure resistance between injector test pin(s) at breakout box and chassis ground. If each resistance is 10,000 ohms or more, replace injector per cylinder balance test service code and repeat QUICK TEST (SEFI) or go to next step (EFI). If each resistance is less than 10,000 ohms, repair short. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

11) Isolate Faulty Injector Circuit Turn ignition off. Install breakout box, and disconnect ECA. Disconnect all injectors on suspect bank. With DVOM set on 200-ohm scale, connect one injector and measure resistance between test pins No. 37 and 58 (injector bank No. 1) or 59 (injector bank No. 2). Disconnect injector, and repeat process for all other injectors. See INDIVIDUAL INJECTOR RESISTANCE . If all injectors are within specification, go to step 12). If injectors are not as specified, replace injector. Remove breakout box, and reconnect components. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST .

12) Check Injector Drive Signal With ignition off and breakout box installed, connect ECA to breakout box. Use a non-powered 12-volt test light, and connect as follows:

Non-SEFI Connect test light between test pins No. 37 and 58 at breakout box. Connect light between test pins No. 37 and 59 at breakout box.
SEFI Connect test light between test pin No. 37 and suspect injector test pin at breakout box.

Crank or start engine. If test light glows dimly, system is operating correctly. Clean injectors, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST and CYLINDER BALANCE TEST. If test light does not glow dimly (no light/bright light), replace ECA. Reconnect all components, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

13) Check Thermactor Operation If vehicle is equipped with pulse-air or does not have thermactor system, go to next step 14). A HEGO which is always lean could be caused by thermactor air being diverted upstream from HEGO sensor. With dual HEGO, Code 41/172 applies to right or rear HEGO and Code 91/136 or 176 applies to left or front HEGO. Turn ignition off. Disconnect thermactor air hose(s) from thermactor pump. Run KOER SELF-TEST . If Code 41/172, 91/136 or 176 is present, reconnect thermactor air hoses and go to step 90). If no codes are present, repair thermactor system as necessary.

14) Check HEGO Integrity A HEGO sensor which is always lean, slow to switch or does not switch could be caused by:

Moisture inside HEGO sensor or connector causing a short to ground.
HEGO sensor coated with contaminants.
HEGO circuit open.
HEGO circuit shorted to ground.

Turn ignition off. Inspect HEGO wiring harness for damage. Inspect HEGO sensor and connector for signs of fluid entry. Repair or replace as necessary. Start engine, and run it at 2000 RPM for 2 minutes. Turn ignition off. Run KOER SELF-TEST . If fault codes are present, go to step 15) (MAP sensor-equipped models) or step 16) (MAF sensor-equipped models). If no code is present, go to step 21).

15) Check HEGO Sensor (Engines With MAP Sensors) Vacuum or air leaks in non-EEC-IV areas could cause Code 41, 91, 136, 172 or 176. Check following possibilities before continuing:

Leaking vacuum actuated motor.
Leaking intake gasket.
EGR system.
PCV system.
Lead-contaminated HEGO sensor.

Turn ignition off. Ensure MAP sensor output voltage is correct. See CIRCUIT TEST DF, step 3). Disconnect appropriate HEGO sensor from vehicle harness. Connect DVOM to HEGO SIGNAL lead at sensor from vehicle harness. On 3-wire HEGO, connect DVOM to HEGO SIGNAL lead at sensor connector and battery negative terminal. On 4-wire HEGO, connect DVOM to HEGO SIGNAL and HEGO GND leads at sensor connector. On all models, disconnect and plug vacuum line at MAP sensor. Start engine, and apply 10-14 in. Hg to MAP sensor. Run engine at 2000 RPM for 2 minutes. If reading is 0.5 volt or more, go to step 17). If reading is less than 0.5 volt, replace HEGO sensor and repeat QUICK TEST .

16) Check HEGO Sensor (Engines With MAF Sensor) Purpose of this test is to verify HEGO sensor can generate a voltage signal of greater than 0.5 volt during KOER SELF-TEST . With ignition off and DVOM set on 20-volt scale, disconnect appropriate HEGO sensor from harness. On 4-wire HEGO, connect DVOM between HEGO SIGNAL and HEGO GND at HEGO sensor connector. On 3-wire HEGO, connect DVOM to HEGO SIGNAL at sensor and battery negative terminal. On all models, run engine at 2000 RPM for 2 minutes. Repeat KOER SELF-TEST and monitor HEGO sensor voltage. If voltage is 0.5 volt or more at end of self-test, go to step 17). If voltage is less than 0.5 volt, replace HEGO sensor and repeat QUICK TEST .

17) Check Continuity Of HEGO Circuits Turn ignition off. Install breakout box, leaving ECA disconnected. Disconnect suspect HEGO sensor from vehicle harness. Inspect both ends of connector for damage, moisture and corrosion. Repair as necessary. Set DVOM on 200-ohm scale. Measure resistance between HEGO SIGNAL (test pin No. 29) at breakout box and HEGO SIGNAL at vehicle harness connector. On 3-wire HEGO, measure resistance between HEGO GROUND test pin at breakout box and battery negative terminal. On 4-wire HEGO, measure resistance between HEGO GROUND test pin at breakout box and HEGO GND at vehicle harness connector. Where applicable, measure resistance between HEGO GND and SIG RTN at breakout box. On all models, go to step 18) if each resistance is less than 5 ohms. If any resistance is 5 ohms or more, repair open circuit. Remove breakout box, and reconnect all components. Drive vehicle for 5 minutes at 55 MPH. Repeat QUICK TEST .

18) Check HEGO Circuit For Short To Ground Turn ignition off. Leave breakout box installed and ECA disconnected. Disconnect HEGO sensor. Measure resistance between HEGO SIGNAL and test pins No. 40, 46 and 49 at breakout box. If any reading is less than 10,000 ohms, repair short to ground. Reconnect all components, and repeat QUICK TEST . If reading is 10,000 ohms or more, go to step 19).

19) Check HEGO Sensor For Short To Ground Disconnect HEGO sensor. On 4-wire HEGO, measure resistance between PWR GND, HEGO GND, SIG RTN and HEGO SIG at HEGO sensor connector. On all HEGO sensors, measure resistance between PWR GND and HEGO SIGNAL at HEGO sensor connector. If resistance is less than 10,000 ohms, replace HEGO sensor. Connect all components, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST . If resistance is 10,000 ohms or more, perform following procedure as applicable.

For Codes 144/41, 139/91, 171, 174, 175 and 178, go to step Step 90) .
For all other codes, go to step 20) if engine is equipped with MAP sensor. If engine is equipped with MAF sensor, replace ECA. Drive vehicle for 5 miles at 55 MPH, and repeat QUICK TEST .

20) Attempt To Eliminate Code 41/172, 91/136 Or 176 (Engines With MAP Sensor) Turn ignition off. Install breakout box. Connect ECA to breakout box. Connect HEGO sensor. Disconnect and plug MAP sensor vacuum hose. Apply 10-14 in. Hg to MAP sensor. Start and run engine at 2000 RPM for 2 minutes. Allow engine to return to idle. Perform KOER SELF-TEST . If diagnosing continuous memory codes, drive vehicle 5 miles at 55 MPH. If Code 41/172, 91/136 or 176 is still present, remove breakout box. Connect all components. If engine runs rough, go to CIRCUIT TEST S, step 2). If engine does not run rough, replace ECA, drive vehicle 5 miles at 55 MPH and repeat QUICK TEST . If code is not present, remove breakout box and connect all components. HEGO input circuit and fuel delivery are okay; fault is in area common to all areas. See TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

21) Check Resistance Of HEGO Heating Element Turn ignition off. Disconnect suspect HEGO sensor. Inspect both ends of connector for damage, moisture and corrosion. Repair if necessary. Set DVOM on 200-ohm scale. Measure resistance between IGNITION RUN circuit and PWR GND circuit at HEGO sensor connector. Hot to warm engine resistance should be 5-30 ohms. Cold engine resistance is 2-5 ohms. If resistance is within specification, go to step 22). If resistance is not as specified, replace HEGO sensor and repeat QUICK TEST.

22) Check For Power At HEGO Harness Connector Disconnect HEGO sensor. Turn ignition on. Measure voltage between IGNITION RUN and PWR GND circuits at HEGO vehicle harness connector. If voltage is 10.5 volts or more, HEGO system and fuel delivery are okay. HEGO sensor may have cooled before KOER SELF-TEST. If driveability symptom continues, fault is in area common to all cylinders. See TESTS W/O CODES article in the ENGINE PERFORMANCE Section. If voltage is less than 10.5 volts, go to step 23).

23) Check Continuity Of Power Ground Circuit Turn ignition off. Measure resistance between PWR GND circuit at HEGO wiring harness connector and negative battery terminal. If resistance is less than 5 ohms, repair open in IGNITION RUN circuit and repeat QUICK TEST. If resistance is 5 ohms or more, repair open in PWR GND circuit and repeat QUICK TEST .

24) Check HEGO SIGNAL For Short To Power On dual HEGO systems, Code 42/173 applies to right or rear HEGO. Codes 92/137 and 177 applies to left or front HEGO. Turn ignition off. Disconnect appropriate HEGO sensor. Turn ignition on. Measure voltage between HEGO SIG and PWR GND at HEGO wiring harness connector. If reading is less than 0.5 volt, go to step 26). If reading is 0.5 volt or more, go to step 25).

25) Check For Short To Power Turn ignition off. Disconnect HEGO sensor. Inspect both ends of connector for damage, moisture and corrosion. Repair if necessary. Disconnect ECA 60-pin connector. Install breakout box, leaving ECA disconnected. Measure resistance between VPWR circuit and HEGO SIG circuit at breakout box. If reading is 10,000 ohms or more, replace ECA. Remove breakout box, and reconnect all components. Drive vehicle 5 miles at 55 MPH. Repeat QUICK TEST . If reading is less than 10,000 ohms, repair short circuit. Remove breakout box, and reconnect all components. Drive vehicle 5 miles at 55 MPH. Repeat QUICK TEST .

26) Check HEGO Sensor For Short To IGNITION RUN Circuit Turn ignition off, and wait 10 seconds. Disconnect HEGO. Set DVOM to 200-k/ohm scale. Measure resistance between IGNITION RUN circuit and HEGO SIG circuit at HEGO sensor connector. If resistance is 10,000 ohms or more, go to step 27) for Codes 42/173, 92/137 and 177 or step 28) (MAP sensor) or 30) (MAF sensor) for codes 171, 174, 175 and 178. If resistance is less than 10,000 ohms, replace HEGO sensor. Drive vehicle for 5 miles at 55 MPH, and repeat QUICK TEST .

27) Attempt To Generate Code 41/172, 91/136 Or 176 Turn ignition off. Disconnect appropriate HEGO sensor. Using jumper wire, connect HEGO SIG circuit at HEGO wiring harness connector to negative battery terminal. Repeat KOER SELF-TEST . If Code 41/172, 91/136 or 176 is present, remove jumper wire and go to step 28) for engines with MAP sensor or step 30) for engines with MAF sensor. If Codes 41/172, 91/136 and 176 are not present, remove jumper wire. Disconnect ECA connector, and inspect it for damage. If connector is okay, replace ECA. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST .

Because MAP sensor greatly influences fuel control, MAP sensor may malfunction without setting Code 22/126. Next 2 steps test MAP vacuum circuit.

28) Check MAP Sensor For Vacuum Leaks Turn ignition off. Disconnect vacuum hose from MAP sensor. Connect vacuum pump to sensor. Apply 18 in. Hg to MAP sensor. If sensor does not hold vacuum, replace MAP sensor. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST . If sensor holds vacuum, release vacuum and go to step 29).

29) Check For Loss Of Vacuum To MAP Sensor Using vacuum "T", connect vacuum gauge in MAP sensor vacuum hose. Start engine. Note vacuum reading at idle stabilizes. Turn ignition off. Remove "T" and vacuum gauge. Reconnect hose to MAP sensor. Connect vacuum gauge at a different manifold vacuum location. Start engine, and note vacuum reading. If readings do not differ by more than 1 in. Hg, go to next step. If readings differ by more than 1 in. Hg, inspect vacuum hoses for leaks, kinks and blockage. Repair as necessary. Connect all components, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST .

30) HEGO Sensor Check Turn ignition off. Disconnect HEGO sensor. For 4-wire HEGO, connect DVOM to HEGO SIGNAL and HEGO GND or SIG RTN at HEGO sensor connector. For 3-wire HEGO, connect DVOM to HEGO SIGNAL at HEGO sensor connector and negative battery terminal. On all models, remove PCV valve from hose. Start engine, and run it at about 2000 RPM. DVOM should indicate less than 0.4 volt within 30 seconds. If voltage is not as specified, replace HEGO sensor. Reconnect vacuum hoses, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST . If voltage is as specified, go to step 90).

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 30) to step 90). No test procedures have been omitted.

90) Check Continuous Monitor Mode Start engine, and warm it to normal operating temperature. Raise engine speed to 2000 RPM for 2 minutes and then return to idle. Enter KOER wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST. While observing DVOM or scan tester, shake or bend small sections of wiring harness from HEGO sensor to ECA. Wiggle, shake or bend small sections of wiring harness from HEGO GND to ECA. If no fault is indicated, remain in CONTINUOUS MONITOR MODE and go to step 91). If fault is indicated, isolate and repair fault as necessary. Clear codes. Repeat QUICK TEST .

91) Continuous Monitor Test Drive Check While still in KOER wiggle test, test drive vehicle for 5 miles at 55 MPH over smooth roads. Drive an additional 5 miles at 55 MPH over rough roads. If possible, drive vehicle through a pool of water to wet HEGO sensor and connector. If fault is indicated, isolate fault and repair as necessary. Clear codes, and remove breakout box. Repeat QUICK TEST . If no codes are indicated, exit KOER wiggle test and go to next step.

92) Check HEGO Switching Turn ignition off. Inspect wire harness for proper routing and insulation. Check for burnt, chaffed or open wires. Repair if necessary. Disconnect ECA 60-pin connector, and inspect it for damaged or pushed-out pins, corrosion and other damage. Repair as necessary. Install breakout box. Connect ECA to breakout box. Connect analog voltmeter to suspect HEGO sensor test pin and HEGO GND at breakout box. Test drive vehicle for 5 miles at 55 MPH while observing voltmeter. HEGO should switch from .3 volt to .9 volt within 3 seconds. If HEGO does not switch as described, replace HEGO sensor. Connect all components, and repeat QUICK TEST . If HEGO switches as described, fault cannot be identified or duplicated at this time. See INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.