Diagnostic Aids

Perform this test when instructed during QUICK TEST, or when directed by other test procedures.

See HOW TO USE CIRCUIT TESTS in this article before performing this test. Fuel contaminated engine oil may affect Codes 41/172, 91/136, 42/173 or 92/137. If this is suspected, remove PCV valve from valve cover and repeat QUICK TEST. If problem is corrected, change engine oil and filter. Use this test to diagnose only the following components:

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

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

Ignition coil, distributor cap or rotor
Faulty or fouled spark plugs or wires
Faulty CANP system
Distributorless Ignition System (DIS)
EGR valve and gasket
Air filter
Fuel or engine oil contamination
Poor electrical ground
Faulty fuel pressure
Intake or exhaust system leaks
Engine below normal operating temperature

4.9L PFI TEST PIN WIRE COLOR I.D.

Pin No.	Ckt. No.	(Ckt. Title)	Wire Color
Pin 29	94	(HEGO)	Red/Black
Pin 37	361	(EPCPWR/VPWR)	Red
Pin 40	60	(PWR GND)	Black/Light Green
Pin 46	359	(SIG RTN)	Gray/Red
Pin 57	361	(VPWR)	Red
Pin 58	96	(INJ BANK 1)	Tan/Orange
Pin 59	95	(INJ BANK 2)	Tan/Red
Pin 60	570	(PWR GND)	Black/Light Green

4.9L PFI TEST PIN WIRE COLOR I.D.

Pin No.	Ckt. No.	(Ckt. Title)	Wire Color
Pin 29	74	(HEGO)	Gray/Light Blue
Pin 37	361	(VPWR)	Red
Pin 40	570	(PWR GND)	Black/White
Pin 46	359	(SIG RTN)	Gray/Red
Pin 49	89	(HEGO GND)	Orange
Pin 57	361	(VPWR)	Red
Pin 58	555	(INJ BANK 1)	Tan
Pin 59	556	(INJ BANK 2)	White
Pin 60	570	(PWR GND)	Black/White

INDIVIDUAL INJECTOR RESISTANCE ⁽¹⁾

Engine

Ohms

4.9L

14.0-17.5

⁽¹⁾	Resistance values are for a single injector.

INJECTOR BANK RESISTANCE

Engine	Ohms
4.9L	4.5-6.0

Fig 1: Test H - Fuel Control System Schematic

1) Check For Contaminated Engine Oil Turn ignition off. Remove PCV valve from valve cover. Inspect valve cover hole and PCV for damage, sludge build up, blockage and movement of valve plunger. Repair as necessary. Perform KOER SELF-TEST. If vehicle is a no start, KOER codes 41/172, 91/136, 42/173 or 92/137, or Continuous Memory Codes 176, 177, 144/41, 91/139, 171, 175, 174 or 178 are set, reinstall PCV valve and go to next step. If no code is set, change engine oil and filter; reinstall PCV valve. Drive vehicle for 5 miles at 55 MPH. Rerun QUICK TEST.

2) Check Fuel Pressure Turn ignition off and wait 10 seconds. 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. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If vehicle is a no start, cycle ignition on and off several times. If fuel pressure is within specification, go to next step. If pressure is not to specification, remove fuel pressure gauge. Repair electric fuel pump or fuel pressure regulator.

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

4) Fuel Delivery Test Ensure fuel is of good quality. With ignition off, install fuel pressure gauge and pressurize fuel system as in step 1). Disconnect inertia switch. Crank engine for 5 seconds. If fuel pressure drop is greater than 5 psi after 5 seconds of cranking, EEC-IV system is not the cause of no-start condition. Check additional no-start tests in the TESTS W/O CODES article in this section. If fuel pressure drop is less than 5 psi, remove fuel pressure gauge and reconnect inertia switch; go to step 7) (for EFI), or step 8) (for SEFI).

5) Cylinder Balance Test: EFI Engines Connect a tachometer to engine. Start engine and run at idle. Disconnect and reconnect injectors one at a time, noting RPM drop as each injector is disconnected. Note that 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 symptoms or 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 Engines ONLY Perform KOER SELF-TEST. After last code is displayed, wait 5-10 seconds. Enter CYLINDER BALANCE TEST by briefly opening throttle for one second (not WOT). Test time is approximately 2-3 minutes. A Code 77/538 indicates throttle is touched when the test is ran, and that test is not completed. To interpret codes received from test, refer to CYLINDER BALANCE TEST SERVICE CODES . If a Cylinder Balance Test Code is displayed, go to step 8). If a Cylinder Balance Test Code is not displayed, fuel delivery is okay; fault is in an area common to all cylinders. 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.

Code 538 could also be outputted if Continuous Memory Code 214 (CID) is present. If Continuous Memory Code 214 is present, see appropriate chart under CODE-TO-TEST MENU(S) for instruction.

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: EFI Engines Turn ignition off and 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 (injector bank No. 1) or 59 (injector bank No. 2) at breakout box. Record resistance. Refer to appropriate INJECTOR BANK RESISTANCE table in this circuit test. If each resistance is within specifications for appropriate engine, 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 Engines Turn ignition off and 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 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 appropriate INJECTOR BANK RESISTANCE table in this circuit test. If each resistance is within specifications for appropriate engine, 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 and wait 10 seconds. Install breakout box, leaving ECA disconnected. Disconnect injector vehicle harness connector at injectors. Set DVOM to 200-ohm scale. Measure resistance between test pin No. 37/57 at breakout box and VPWR pin at each injector vehicle harness connector. See the TEST H - FUEL CONTROL SYSTEM SCHEMATIC, Fig. Fig 1 , near the beginning of this circuit test. Measure resistance between injector test pin(s) at breakout box and the same injector circuit signal pin at each injector vehicle harness connector. If each resistance is less than 5 ohms, go to next step. If each resistance is greater than 5 ohms, repair open circuit. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Rerun QUICK TEST.

10) Check Injector Harness Circuit 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 the TEST H - FUEL CONTROL SYSTEM SCHEMATIC Fig. Fig 1 , near the beginning of this circuit test. Set DVOM to 200-k/ohm scale. Measure resistance between injector test pin(s) and test pins No. 37/57, 40, 46 and 60. Measure resistance between injector test pin(s) at breakout box and chassis ground. If each resistance is greater than 10 k/ohms, replace injector per cylinder balance test service code and rerun QUICK TEST (for SEFI), or go to next step (for EFI). If each resistance is less than 10 k/ohms, repair short. Remove breakout box, reconnect all components and drive vehicle for 5 miles at 55 MPH. Rerun QUICK TEST.

11) Isolate Faulty Injector Circuit Turn ignition off. Install breakout box and disconnect ECA. Disconnect all injectors on suspected bank. With DVOM set on 200-ohm scale, connect one injector and measure resistance between test pins No. 37 and 58 or 59. Disconnect injector and repeat process for all other injectors. See appropriate INDIVIDUAL INJECTOR RESISTANCE table for specifications. If all injectors are within specifications, go to step 12). If injectors are not as specified, remove breakout box. Reconnect ECA and injectors. Repair open or short in injector harness. If circuit is okay, replace injector. Drive vehicle for 5 miles at 55 MPH. Rerun 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:

EFI Engines - 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.
Sequential PFI Engines (SEFI) - Connect test light between test pin No. 37 and the suspected injector(s) test pin at breakout box.

Crank or start engine. If test light glows dimly, system is operating properly. remove breakout box and reconnect ECA. Clean and test injectors. Drive vehicle for 5 miles at 55 MPH. Rerun QUICK TEST and CYLINDER BALANCE TEST.

If test light does not glow dimly (no light/bright light), check injector circuit for shorts to ground. If system is okay, remove breakout box and replace ECA. Remove breakout box and reconnect all components. Drive vehicle for 5 miles at 55 MPH. Rerun QUICK TEST.

13) Check Thermactor Operation If vehicle is equipped with Pulse-Air or does not have Thermactor System, ignore this step and go to next step. With dual HEGO, code 41/172 refers to right or rear HEGO, and code 91/136 or 176 refers to left or front HEGO. A HEGO that is always lean could be caused by Thermactor air being diverted upstream from HEGO sensor. Turn ignition off and wait 10 second. Disconnect Thermactor air hose(s) from Thermactor pump. Run KOER SELF-TEST. If codes 41/172, 91/136 or 176 are present, reconnect Thermactor air hose(s) and go to next step. If codes 41/172, 91/136 or 176 are not present, repair thermactor system as necessary.

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

Moisture inside HEGO sensor, or harness connector causing a short to ground
HEGO sensor coated with containments
HEGO circuit open
HEGO circuit shorted to ground

Turn ignition off and wait 10 seconds. Inspect HEGO harness for chaffing, burns or other indications of damage; repair or replace as necessary. Inspect HEGO sensor and connector for signs of water entry; repair or replace as necessary. Start engine and run at 2000 RPM for 2 minutes. Turn ignition off and wait 10 seconds. Run KOER SELF-TEST. If fault codes are present, go to next step (for MAP sensor-equipped vehicles), or step 16) (for MAF sensor-equipped vehicles). If no code is present, go to step 21).

15) Checking HEGO Sensor On Engines With MAP Sensors Turn ignition off and set DVOM on 20-volt scale. Disconnect appropriate HEGO sensor from vehicle harness. Connect DVOM to HEGO SIGNAL lead at sensor connector and battery negative terminal (3-wire HEGO). Connect DVOM to HEGO SIGNAL and HEGO GND leads at sensor connector (4-wire HEGO). Disconnect and plug vacuum line MAP sensor. Start engine and apply 10-14 in Hg to Manifold Absolute Pressure (MAP) sensor. Run engine at 2000 RPM for 2 minutes. If reading is greater than 0.5 volt within 2 minutes, go to step 17). If reading is less than 0.5 volt within 2 minutes, replace HEGO sensor; reconnect MAP and rerun QUICK TEST.

Vacuum or air leaks in non-EEC-IV related areas may cause Code 41 or 91. Check the following areas: leaking vacuum actuator (A/C control motor, etc.) engine seals, EGR system, PCV system and lead contamination of HEGO sensor.

Fig 1: Checking HEGO Sensor

16) Check HEGO Sensor On Engines With MAF Sensor The 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. Depending on type of sensor (3 wires or 4 wires), connect DVOM as follows:

4-Wire HEGO Sensors - Connect DVOM between HEGO SIGNAL and HEGO GND at HEGO sensor connector.
3-Wire HEGO Sensors - Connect DVOM to HEGO SIGNAL at sensor and battery negative terminal.

Rerun KOER SELF-TEST and monitor HEGO sensor voltage. If voltage is greater than 0.5 volt, go to next step. If voltage is less than 0.5 volt, replace HEGO sensor and rerun QUICK TEST.

Fig 1: Checking HEGO Sensor

17) Check Continuity Of HEGO SIGNAL & HEGO GROUND Circuits Turn ignition off. Install breakout box, leaving ECA disconnected. Disconnect suspected HEGO sensor from vehicle harness. Inspect both ends of connector for damage or pushed-out pins, moisture, corrosion, loose wires or other damage. 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 sensors, measure resistance between HEGO GROUND test pin at breakout box and battery negative terminal.

On 4-Wire HEGO sensors, 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.

If each resistance is less than 5 ohms, go to next step. If each resistance is greater than 5 ohms, repair open circuit. Remove breakout box and reconnect all components. Drive vehicle for 5 minutes at 55 MPH. Rerun QUICK TEST.

18) Check HEGO Circuit For Short To Ground Turn ignition off. Leave breakout box installed and ECA disconnected. Disconnect HEGO sensor and set DVOM on 200-k/ohm scale. Measure resistance between HEGO SIGNAL (test pin No. 29) and test pins No. 40, 46 and 49 at breakout box. If any reading is less than 10 k/ohms, repair short to ground; remove breakout box, reconnect all components and repeat QUICK TEST. If reading is 10 k/ohms or more, go to next step.

19) Check HEGO Sensor For Short To Ground With ignition off, breakout box installed and ECA disconnected, set DVOM to 200-k/ohm scale. Disconnect HEGO sensor. Measure resistance between PWR GND and HEGO SIGNAL at HEGO sensor connector. For trucks with 4-wire sensors, measure resistance between PWR GND, HEGO GND, SIG RTN and HEGO SIG at HEGO sensor connector. If resistance is less than 10 k/ohms, replace HEGO sensor and remove breakout box; reconnect all components, drive vehicle for 5 miles at 55 MPH and repeat QUICK TEST. If resistance is greater than 10 k/ohms, perform the following procedure as applicable.

For codes 144/41, 139/91, 171, 174, 175 or 178, go to step 90).
On engines with MAP sensor, go to step 20).
On engines with MAF sensor, remove breakout box. Reconnect HEGO sensor and replace ECA. Drive vehicle for 5 miles at 55 MPH. Rerun QUICK TEST.

20) Attempt To Eliminate Code 41/172, 91/136 Or 176: Engines With MAP Sensor Turn ignition off. Install breakout box; reconnect ECA and HEGO sensor. Ensure MAP sensor vacuum hose is disconnected and plugged. 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 you are here for Continuous Memory Codes, vehicle has to be driven 5 miles at 55 MPH. If Code 41/172, 91/136 or 176 is still present, remove breakout box. Reconnect ECA and MAP sensor vacuum line. If engine still runs rough, go to TEST S, step 2). If engine does not run rough, replace ECA; drive vehicle 5 miles at 55 MPH then repeat QUICK TEST.

If Code 41/172, 91/136 or 176 is not present, remove breakout box and reconnect ECA and MAP sensor vacuum hose. HEGO input circuit and fuel delivery are okay; fault is in area common to all areas. Service as necessary.

21) Check Resistance Of HEGO Heating Element Turn ignition off. Disconnect suspected HEGO sensor. Inspect both ends of connector for damaged or pushed-out pins, moisture, corrosion, loose wires or other damage. Repair as necessary. Set DVOM on 200-ohm scale. Measure resistance between KPWR circuit and PWR GND circuit at HEGO sensor connector. Hot to warm resistance should be 5.0-30.0 ohms. Room temperature resistance is 2.0-5.0 ohms. If resistance is within specification, go to next step. If resistance is not as specified, replace HEGO sensor and repeat QUICK TEST.

Fig 2: Checking HEGO Sensor

22) Check For Power At HEGO Harness Connector With ignition on and engine off, and HEGO disconnected, set DVOM on 20-volt scale. Measure voltage between KEY POWER circuit and PWR GND circuit at HEGO vehicle harness connector. If voltage is greater than 10.5 volts, HEGO system and fuel delivery are okay; HEGO sensor may have cooled before KOER SELF-TEST. If driveability symptom persists, fault is in area common to all cylinders, such as air or vacuum leaks, fuel contamination, EGR, MAP, etc. If voltage is less than 10.5 volts, go to next step.

Fig 3: Identifying HEGO Sensor Harness Connector

23) Check Continuity Of Power Ground Circuit Turn ignition off and wait 10 seconds. Disconnect HEGO sensor and set DVOM on 200-ohm scale. Measure resistance between PWR GND circuit at HEGO vehicle harness connector and battery negative post. If resistance is less than 5 ohms, repair open in KEY POWER circuit. Reconnect HEGO and rerun QUICK TEST. If resistance is more than 5 ohms, reconnect HEGO sensor and repair open in PWR GND circuit. Reconnect HEGO sensor and rerun QUICK TEST.

24) Check HEGO SIGNAL For Short To Power On dual HEGO systems, Code 42/173 refers to right (or rear) side HEGO, and Code 92/137 or 177 refers to left (or front) side HEGO. Turn ignition off and wait 10 seconds. Disconnect appropriate HEGO sensor. Set DVOM on 20-volt scale. With ignition on and engine off, measure voltage between HEGO SIG and PWR GND at HEGO vehicle harness connector. If reading is less than .5 volt, go to step 26). If reading is NOT less than 0.5 volt, go to next step.

Fig 4: Identifying HEGO Sensor Harness Connector

25) Check For Short To Power Turn ignition off. Disconnect HEGO sensor. Inspect both ends of connector for damaged or pushed-out pins, moisture, corrosion, loose wires or other damage. Repair as necessary. Set DVOM on 200-k/ohm scale. Disconnect ECA 60-pin connector. Install breakout box, leaving ECA disconnected. Measure resistance between KEY POWER circuit and HEGO SIG circuit at breakout box.

If reading is greater than 10 k/ohms, replace ECA. Remove breakout box and reconnect all components. Drive vehicle for 5 miles at 55 MPH. Rerun QUICK TEST.

If reading is less than 10 k/ohms, repair short circuit. Remove breakout box and reconnect all components. Drive vehicle for 5 miles at 55 MPH. Rerun 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 KEY POWER circuit and HEGO SIG circuit at HEGO sensor connector.

If resistance is greater than 10 k/ohms, go to next step for codes 42/173, 92/137 or 177. For codes 171, 174, 175 or 178, go to step 28) (MAP sensor), or step 30) (MAF sensor).

If resistance is less than 10 k/ohms, replace HEGO sensor. Drive vehicle for 5 miles at 55 MPH and rerun QUICK TEST.

Fig 5: Checking HEGO Sensor

27) Attempt To Generate Code 41/172, 91/136 Or 176 The following non-EEC areas may cause these codes: fuel-contaminated engine oil, ignition misfire and faulty CANP system. Turn ignition off and wait 10 seconds. Disconnect appropriate HEGO sensor. Using jumper wire, connect HEGO SIG circuit at HEGO vehicle harness connector to battery negative terminal. Repeat KOER SELF-TEST.

If Code 41/172, 91/136 or 176 is present, remove jumper wire and go to next step for engines with MAP. For all other engines, go to step 30).

If Codes 41/172, 91/136 or 176 is not present, remove jumper wire. Disconnect ECA connector and inspect for damage. If connector is okay, replace ECA. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

Because MAP sensor has a large influence on fuel control, Code 42/172 or 91/136 may be caused by a faulty MAP sensor, even though Code 22/126 has not been set. The next 2 steps test the MAP vacuum circuit.

28) Check MAP Sensor For Vacuum Leaks Turn ignition off and wait 10 seconds. Disconnect vacuum hose from MAP sensor and connect vacuum pump to sensor. Apply 18 in Hg to MAP sensor. If sensor holds vacuum, release vacuum and go to next step. If sensor does not hold vacuum, replace MAP sensor. Remove vacuum pump. Connect vacuum hose and reconnect HEGO. Drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.

29) Check For Loss Of Vacuum To MAP Sensor Using a vacuum "T", connect vacuum gauge in intake manifold vacuum hose at MAP sensor. Start engine and note vacuum reading at a stable idle. Turn ignition off and wait 10 seconds. Remove "T" and vacuum gauge. Reconnect hose to MAP sensor. Connect vacuum gauge at a different intake manifold 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, or blockage. Repair as necessary. Reconnect all components and drive vehicle for 5 miles at 55 MPH. Rerun QUICK TEST.

30) HEGO Sensor Check Turn ignition off and wait 10 seconds. Disconnect HEGO sensor. Set DVOM on 20-volt scale. For 4-Wire HEGO, connect DVOM to HEGO SIGNAL and HEGO GND at HEGO sensor connector. For 3-Wire HEGO, connect DVOM to HEGO SIGNAL at HEGO sensor connector and battery negative post. Remove a vacuum hose to create vacuum leak, which will cause HEGO sensor to go lean. Start engine and run at approximately 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 next step.

Fig 1: Checking HEGO Sensor

NOTE: There is a break in the step numbering sequence at this point, skipping from step 30) to step 90). Break is due to previous chart references to these testing procedures. No test procedures have been omitted.

90) Check Continuous Monitor Mode Turn ignition off and wait 10 seconds. Ensure engine is at normal operating temperature. Start engine and run at 2000 RPM for 2 minutes then return to idle. Enter KOER wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST) under QUICK TEST. While observing DVOM or "Scan" Tool, wiggle, shake or bend small sections of EEC-IV wiring harness from HEGO sensor to ECA. Wiggle, shake or bend small sections of EEC-IV wiring harness from HEGO GND to ECA. If no fault is indicated, remain in CONTINUOUS MONITOR MODE and go to next step. If fault is indicated, isolate and repair fault as necessary. Clear codes, remove breakout box and reconnect all components. Rerun QUICK TEST.

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

92) Check HEGO Switching Turn ignition off and wait 10 seconds. Inspect EEC-IV wire harness for proper routing and insulation. Check for burnt, chaffed or intermittently shorted or open wires. Repair as necessary. Disconnect ECA 60-pin connector and inspect for damaged or pushed-out pins, corrosion, loose wires or other damage; repair as necessary. Install breakout box and connect ECA to breakout box. Connect analog voltmeter to suspected 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. Remove breakout box, reconnect all components and rerun QUICK TEST. If HEGO switches as described, fault cannot be identified or duplicated at this time. See INTERMITTENTS in the TESTS W/O CODES article in this section.