Test Procedure

H1 CHECK FOR DIAGNOSTIC TROUBLE CODES (DTCS)

Are DTCs P0171, P0172, P0174, P0175, P2195, P2196, P2197, P2198, P2270, P2271, P2272, P2273, P2274, or P2275 present?

Yes	No
For DTCs P2270, P2271, P2272, P2273, P2274 or P2275, GO to H32. For DTCs P0171, P0174, P2195 or P2197, GO to H2. For DTCs P0172, P0175, P2196 or P2198, GO to H8.	For all others, GO toDIAGNOSTIC TROUBLE CODE (DTC) CHARTS AND DESCRIPTIONS .

H2 DTCS P0171, P0174, P2195 OR P2197: LEAN SYSTEM DTCS

NOTE: Do not clear the DTCs or reset the keep alive memory (KAM).

Access the PCM and record the engine coolant temperature (ECT) PID from the freeze frame data. The freeze frame data is used to recreate the concern.
Retrieve and record the self-test DTCs.
Are any DTCs present other than the following: P0171, P0174, P2195 or P2197?

Yes	No
DISREGARD the current diagnostic trouble code (DTC) at this time. DIAGNOSE the next DTC. GO toDIAGNOSTIC TROUBLE CODE (DTC) CHARTS AND DESCRIPTIONS .	GO to H3.

H3 CARRY OUT A VISUAL INSPECTION ON THE INTAKE AIR SYSTEM AND ALL VACUUM HOSES

Key in OFF position.
Check the intake air system for leaks, obstructions, and damage.
Inspect the entire length of all the vacuum hoses for:
- proper connections
- damage or cracks
- damaged or cracked vacuum tees
Verify the integrity of the positive crankcase ventilation (PCV) system.
Verify the proper PCV valve part number.
Is a concern present?

Yes	No
GO to H6.	GO to H4.

H4 CHECK FOR THE PRESENCE OF A VACUUM LEAK

NOTE: Fuel trim values at idle are more sensitive to a vacuum leak. The vacuum leak (unmetered air) represents a larger portion of the total air flow at idle than at part throttle.

NOTE: The barometric pressure (BARO) PID is not a recommended PID to monitor when diagnosing a vacuum leak. Barometric pressure is calculated during high engine load, when the vacuum leak represents a small portion of the total air flow.

NOTE: When calculating the total fuel correction in the following steps, if LONGFT1 equals +13% and SHRTFT1 equals +23%, the total fuel correction for bank 1 equals +36%. If LONGFT2 equals +24% and SHRTFT2 equals -3% the total fuel correction for bank 2 equals +21%.

NOTE: If the freeze frame ECT PID is available, stabilize the engine at the temperature recorded by the freeze frame ECT PID. If the freeze frame ECT PID is not available, maintain the engine coolant temperature between 82°C - 101°C (180°F - 215°F) and the intake air temperature less than 46°C (115°F).

Key ON, engine running.
Access the PCM and monitor the ECT, CHT and IAT PIDs.
Access the PCM and monitor the LONGFT1, SHRTFT1, LONGFT2 and SHRTFT2 PIDs.
Allow the engine to stabilize at the temperature necessary to recreate the concern.
Mathematically add and record the LONGFT PID value to the SHRTFT PID value for each bank, for a total fuel correction at idle.
Increase the engine speed to 2,500 RPM for 10 seconds.
Record the LONGFT1, SHRTFT1, LONGFT2, and SHRTFT2 PID values.
Mathematically add and record the LONGFT PID value to the SHRTFT PID value for each bank, for a total fuel correction at 2,500 RPM.
Is the total fuel correction value difference, between idle and 2,500 RPM, less than 15 percent?

Yes	No
No vacuum leak is present. For DTCs P0171, P0174, P2195, or P2197 with a secondary air injection (AIR) system, GO to H7. For DTCs P0171 or P0174 without a secondary air injection (AIR) system, GO to H16. For DTCs P2195 or P2197 without a secondary air injection (AIR) system, GO to H10.	GO to H5.

H5 LOCATE THE VACUUM LEAK

CAUTION: Do not clamp or pinch a hard plastic hose. Use a vacuum cap or equivalent to restrict the hose.

NOTE: Restricting the EVAP vapor hose while the EVAP emission canister is purging may shift the SHRTFT. Carry out a visual inspection as necessary.

NOTE: When monitoring for a decrease in the SHRTFT PIDs in the following steps, if SHRTFT1 equals +15% and the hose is restricted, SHRTFT1 decreases to -7%. The total decrease in the SHRTFT PIDs equals 22%.

Locate the vacuum tees for the intake air and PCV systems.
Access the PCM and monitor the SHRTFT1 and SHRTFT2 PIDs.
Restrict the vacuum lines one at a time for 30 seconds. If a vacuum leak is present, the SHRTFT PID values decrease as the hose is restricted.
Is the decrease in the SHRTFT PIDs greater than 15 percent when one of the vacuum hoses is restricted?

Yes	No
GO to H6.	INSPECT the intake air system for a vacuum leak in the intake manifold or intake gaskets. REPAIR as necessary. For repair verification, GO to H6.

H6 VACUUM LEAK REPAIR VERIFICATION

Access the PCM and monitor the SHRTFT1 and SHRTFT2 PIDs.
Allow the engine to stabilize at the temperature necessary to recreate the concern.
Record the SHRTFT1 and SHRTFT2 PID values.
Key in OFF position.
Repair the vacuum leak.
Key ON, engine running.
Allow the engine to stabilize at the temperature necessary to recreate the concern.
Access the PCM and monitor the SHRTFT1 and SHRTFT2 PIDs.
Compare the recorded SHRTFT PID values, prior to the vacuum leak repair, to the current SHRTFT PID values.
Is the decrease in the SHRTFT PIDs greater than 15 percent?

Yes	No
RESET the keep alive memory (KAM). REFER to RESETTING THE KEEP ALIVE MEMORY (KAM) . REPEAT the self-test.	A vacuum leak is still present. GO to H5.

H7 CHECK FOR SECONDARY AIR LEAKS

NOTE: An HO2S always lean condition can be caused by:

leaks in the hoses from the secondary air injection pump to the engine.
secondary air diverted upstream of the HO2S.

Disconnect the secondary air injection hose(s) from the engine and the plug side of the secondary air injection system.
Key ON, engine running.
Carry out the self-test.
Are DTCs P0171, P0174, P2195 or P2197 present?

Yes	No
For DTCs P0171 or P0174, GO to H16. For DTCs P2195 or P2197, GO to H10.	GO to Test HM step 18 .

H8 DTCS P0172, P0175, P2196 OR P2198: RICH SYSTEM DTCS

NOTE: Do not clear the DTCs or reset the keep alive memory (KAM).

Access the PCM and record the freeze frame data.
Retrieve and record the self-test DTCs.
Are any DTCs present other than the following: P0172, P0175, P2196 or P2198?

Yes	No
DISREGARD the current diagnostic trouble code (DTC) at this time. DIAGNOSE the next DTC. GO toDIAGNOSTIC TROUBLE CODE (DTC) CHARTS AND DESCRIPTIONS .	GO to H9.

H9 INSPECT THE ENTIRE INTAKE AIR SYSTEM FOR DEBRIS, BLOCKAGE OR OTHER DAMAGE

Check the intake air system for obstructions, restrictions, and damage.
Check the throttle plate for obstructions or sludge.
Check the air filter element and housing for blockage.
Is a concern present?

Yes	No
REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test.	For DTCs P0172 or P0175, GO to H16. For DTCs P2196 or P2198, GO to H14.

H10 CHECK THE HO2S AND SIGRTN CIRCUIT(S) FOR AN OPEN IN THE HARNESS

Key in OFF position.
Disconnect the HO2S related to the current DTC.
PCM connector disconnected.

Measure the resistance between:

( + ) HO2S Connector, Harness Side	( - ) PCM Connector, Harness Side
HO2S Signal	HO2S Signal
SIGRTN	SIGRTN

Are the resistances less than 5 ohms?

Yes	No
GO to H11.	REPAIR the open circuit. CLEAR the DTCs. REPEAT the self-test.

H11 CHECK THE HO2S CIRCUIT FOR A SHORT TO SIGRTN IN THE HARNESS

Measure the resistance between:

( + ) HO2S Connector, Harness Side	( - ) HO2S Connector, Harness Side
HO2S Signal	SIGRTN

Is the resistance greater than 10K ohms?

Yes	No
GO to H12.	REPAIR the short circuit. CLEAR the DTCs. REPEAT the self-test.

H12 CHECK THE HO2S CIRCUIT FOR A SHORT TO GROUND IN THE HARNESS

Measure the resistance between:

( + ) HO2S Connector, Harness Side	( - )
HO2S Signal	Ground

Is the resistance greater than 10K ohms?

Yes	No
GO to H13.	REPAIR the short circuit. CLEAR the DTCs. REPEAT the self-test.

H13 HO2S CIRCUIT TEST (WITH LEAN DTCS)

PCM connector connected.

Connect a 5 amp fused jumper wire between the following:

Point A HO2S Connector, Harness Side	Point B HO2S Connector, Harness Side
HO2S Signal	VPWR

Key ON, engine OFF.
Access the PCM and monitor the HO2S Signal PID.
Is the voltage greater than 1.3 V?

Yes	No
GO to H16.	GO to H42.

H14 HO2S CIRCUIT TEST (WITH RICH DTCS)

Disconnect the HO2S related to the current DTC.
Key ON, engine OFF.
Access the PCM and monitor the HO2S Signal PID.
Is the voltage less than 0.2 V?

Yes	No
GO to H16.	GO to H15.

H15 CHECK THE HO2S CIRCUIT FOR A SHORT TO THE VPWR OR HEATER IN THE HARNESS

Key in OFF position.
PCM connector disconnected.

Measure the resistance between:

( + ) PCM Connector, Harness Side	( - ) PCM Connector, Harness Side
HO2S Signal	HO2S Heater
HO2S Signal	VPWR

Are the resistances greater than 10K ohms?

Yes	No
GO to H42.	REPAIR the short circuit. CLEAR the DTCs. REPEAT the self-test.

H16 CHECK THE FUEL PRESSURE

WARNING: When checking the fuel system remember that the fuel system may still be pressurized when the engine is switched off. Always follow the instructions related to fuel system pressure relief. All fuel handling safety precautions must be observed. Failure to follow these instructions may result in personal injury.

NOTE: For vehicle specific fuel pressure ranges, refer to the Fuel System Specification Chart in pinpoint test HC.

Remove the jumper wire(s).
HO2S connector connected.
Relieve the fuel pressure. Refer to the appropriate FUEL SYSTEM - GENERAL INFORMATION article for the Fuel System Pressure Release procedure.
Mechanical fuel pressure gauge connected.
Pressurize the fuel system. Refer to the appropriate FUEL SYSTEM - GENERAL INFORMATION article for the Fuel System Pressure Release procedure to pressurize the fuel system.
Key ON, engine running.
Allow the fuel pressure to stabilize.
Key in OFF position.
Key ON, engine running.
Access the PCM and control the FP PID.
Run the fuel pump to obtain maximum fuel pressure.
Is the fuel pressure within range for the vehicle being diagnosed?

Yes	No
GO to H17.	refer to PINPOINT TEST HC .

H17 CHECK THE FUEL SYSTEM FOR PRESSURE STABILITY - FAST LEAKDOWN

NOTE: When the fuel pump is commanded off, the fuel pressure may substantially decrease and then stabilize.

NOTE: During output state control, the fuel pump stays commanded on for only about 5 seconds.

Key in OFF position.
Key ON, engine OFF.
Access the PCM and control the FP PID.
Run the fuel pump to obtain maximum fuel pressure.
Command the fuel pump off.
Allow the fuel pressure to stabilize.
Record the stabilized reading.
Monitor the fuel pressure for 10 seconds.
Does the fuel pressure remain within 34 kPa (5 psi) of the recorded reading after 10 seconds?

Yes	No
GO to H19.	GO to H18.

H18 CHECK FOR AN EXTERNAL FUEL LEAK

Inspect the fuel tank, lines, and filler pipe for a fuel leak.
Is a concern present?

Yes	No
REPAIR as necessary. REFER to the fuel system WARNING information at the beginning of Pinpoint Test HC. refer to PINPOINT TEST HC . CLEAR the DTCs. REPEAT the self-test.	GO to H26.

H19 CHECK THE FUEL SYSTEM FOR PRESSURE STABILITY - SLOW LEAKDOWN

Continue to monitor the fuel pressure for 1 minute.
Does the fuel pressure remain within 34 kPa (5 psi) of the recorded reading (MRFS) or greater than 275 kPa (40 psi) (ERFS) after 1 minute?

Yes	No
GO to H20.	GO to HC13.

H20 CHECK THE SEPARATION LEVEL OF THE ETHANOL/WATER MIXTURE AND GASOLINE IN THE FUEL

NOTE: This step requires the use of a locally obtained 200 ml beaker and a 25 ml graduated cylinder.

NOTE: After approximately 3 minutes of standing, the ethanol and water mixes together and settles to the bottom of the 25 ml graduated cylinder. The gasoline rises to the top.

Fill the 200 ml beaker with 5 ml of clean water.
Use the pressure relief valve on the mechanical fuel gauge to drain 22 ml of fuel into an approved clean container.
Pour 20 ml of fuel from the approved clean container into the 25 ml graduated cylinder.
Add enough water from the 200 ml beaker to the 25 ml graduated cylinder to bring the total volume of liquid to 24 ml.
Insert a stopper plug in the opening of the 25 ml graduated cylinder.
Firmly hold the stopper in place and shake the 25 ml graduated cylinder to mix the water and fuel.
Allow the liquid to stand and separate for approximately 3 minutes.
Record the separation level from the 25 ml graduated cylinder where the ethanol/water mixture and gasoline meet.
Did the ethanol/water mixture and gasoline separate?

Yes	No
GO to H21.	COMPLETE all steps before continuing. The ethanol/water mixture will separate from the gasoline. If the fuel does not appear to separate, then the fuel is either 100% ethanol or a mixture of ethanol and water.

H21 CALCULATE THE PERCENTAGE OF ETHANOL IN THE FUEL

NOTE: Use the illustration as an example for calculating the percentage of ethanol in the following steps. If the separation level is at 14 ml the calculation becomes; 14 minus 4, then multiply by 5 to equal 50. The percentage of ethanol in the fuel is 50%.

Key in OFF position.
Take the recorded separation level from the previous step and subtract the amount of water added.

Multiply the new value by 5. This new value is the percentage of ethanol in the fuel.

Fig 1: Calculating Ethanol In Fuel

Courtesy of FORD MOTOR CO.

Item Number	Description
1	Stopper
2	Gasoline
3	Separation Point at 14 ml
4	Ethanol/Water Mixture

Record the calculated percentage of ethanol in the fuel.
Is any ethanol present in the fuel?

Yes	No
For flex fuel vehicles, GO to H22. For all others, GO to H25.	GO to H26.

H22 COMPARE THE FF_INF PID TO THE CALCULATED PERCENTAGE OF ETHANOL

NOTE: When determining if the FF_INF PID value is within 50% of the calculated percentage of ethanol, if the calculated percentage of ethanol value is 40% then the PID value should be between 0 - 90%. The PID value cannot be less than zero.

Key ON, engine OFF.
Access the PCM and monitor the FF_INF PID.
Compare the FF_INF PID to the calculated percentage of ethanol.
Is the FF_INF PID value within 50% of the calculated percentage of ethanol?

Yes	No
GO to H26.	GO to H23.

H23 RESET THE PERCENT ETHANOL PARAMETER IN THE PCM

NOTE: Certain customer fueling practices such as only fueling with small amounts of fuel or repeatedly switching between gasoline and an ethanol blend greater than E15 may prevent the PCM from learning the correct ethanol content in the fuel.

Reset the keep alive memory (KAM). Refer to RESETTING THE KEEP ALIVE MEMORY (KAM) .
Key ON, engine running.
Access the PCM and monitor the FF_LRND PID.
Drive the vehicle approximately 11.3 km (7 miles) or until the FF_LRND PID indicates yes.
Is the PID state YES?

Yes	No
GO to H24.	GO to H42.

H24 COMPARE THE UPDATED FF_INF PID TO THE CALCULATED PERCENTAGE OF ETHANOL

Key in OFF position.
Key ON, engine OFF.
Access the PCM and monitor the FF_INF PID.
Is the FF_INF PID value within 50% of the calculated percentage of ethanol?

Yes	No
RETURN the vehicle to the customer. ADVISE the customer of the correct fueling practices when using flex fuel. REFER to the Owner's Literature for additional information. ADVISE the customer to continue to use the same fuel for the next 2-3 refuels. This practice helps to verify the PCM is learning the correct percentage of ethanol in the fuel.	A fuel system concern may be present, which prevents the PCM from learning the correct percentage of ethanol in the fuel, GO to HC13.

H25 DETERMINE IF THE PERCENTAGE OF ETHANOL IN THE FUEL IS LESS THAN 25%

Check the recorded calculated percentage of ethanol in the fuel.
Is the calculated percentage of ethanol in the fuel less than 25%?

Yes	No
GO to H26.	REPAIR as necessary. ADVISE the customer of the correct fuel type required for this vehicle. REFER to the Owner's Literature for additional information. CLEAR the DTCs. REPEAT the self-test.

H26 FLOW TEST

Key in OFF position.
PCM connector connected.
Flow test the injector using the fuel injector tester.
Is the flow rate for each injector within specification?

Yes	No
For DTCs P0171, P0172, P0174 or P0175, GO to DC28 . For DTCs P2195 or P2197, GO to H27. For DTCs P2196 or P2198, GO to H28.	INSTALL a new fuel injector. REFER to the appropriate FUEL CHARGING AND CONTROLS article. RESET the keep alive memory (KAM). REFER to RESETTING THE KEEP ALIVE MEMORY (KAM) . REPEAT the self-test.

H27 CHECK THE HO2S OUTPUT VOLTAGE

HO2S connector disconnected.
Visually inspect the HO2S circuit for exposed wiring, contamination, corrosion and correct assembly. Repair as necessary.

Measure the voltage between:

( + ) HO2S Connector, Component Side	( - ) HO2S Connector, Component Side
HO2S Signal	SIGRTN

Increase the engine speed to 2,000 RPM for 3 minutes.
Carry out the KOER self-test.
Monitor the signal voltage during the self-test.
Is the voltage greater than 0.5 volt at any time during the self-test?

Yes	No
GO to H30.	INSTALL a new HO2S. REFER to the appropriate ELECTRONIC ENGINE CONTROLS article. RESET the keep alive memory (KAM). REFER to RESETTING THE KEEP ALIVE MEMORY (KAM) . REPEAT the self-test.

H28 ATTEMPT TO RETRIEVE DTC P2195 OR P2197

HO2S connector disconnected.

Connect a 5 amp fused jumper wire between the following:

Point A HO2S Connector, Harness Side	Point B Vehicle Battery
HO2S Signal	Negative terminal

Carry out the KOER self-test.
Are DTCs P2195 or P2197 present?

Yes	No
GO to H29.	GO to H42.

H29 HO2S VOLTAGE CHECK

Key in OFF position.
Remove the jumper wire(s).
HO2S connector disconnected.
Key ON, engine running.
Increase the engine speed to 2,000 RPM for 30 seconds.

Measure the voltage between:

( + ) HO2S Connector, Component Side	( - ) HO2S Connector, Component Side
HO2S Signal	SIGRTN

Carry out the KOER self-test.
Monitor the signal voltage during the self-test.
Is the voltage less than 0.4 volt at any time during the self-test?

Yes	No
GO to H30.	INSTALL a new HO2S. REFER to the appropriate ELECTRONIC ENGINE CONTROLS article. RESET the keep alive memory (KAM). REFER to RESETTING THE KEEP ALIVE MEMORY (KAM) . REPEAT the self-test.

H30 CARRY OUT A THOROUGH WIGGLE TEST ON THE HO2S HARNESS

Key in OFF position.
HO2S connector connected.
Key ON, engine running.
Engine at normal operating temperature.
Access the PCM and monitor the HO2S Signal PID.
Wiggle, shake, and bend small sections of the wiring harness while working from the sensor to the PCM.
While monitoring the HO2S PID, does the HO2S stop switching?

Yes	No
ISOLATE the concern and REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test.	GO to H31.

H31 TEST DRIVE THE VEHICLE WHILE MONITORING THE HO2S PID FOR SWITCHING

Access the PCM and monitor the HO2S Signal and FUELSYS PIDs.
Start the engine and let idle until the vehicle goes into the closed loop fuel condition.
Drive the vehicle in a manner consistent with the freeze frame data in an attempt to simulate the original concern.
Does the HO2S PID switch?

Yes	No
GO to Test DC step 28 .	INSTALL a new HO2S. REFER to the appropriate ELECTRONIC ENGINE CONTROLS article. RESET the keep alive memory (KAM). REFER to RESETTING THE KEEP ALIVE MEMORY (KAM) . REPEAT the self-test.

H32 DTCS P2270, P2272, P2271, P2273, P2274 OR P2275: HO2S LACK OF SWITCHES STUCK LEAN OR RICH

NOTE: Address all continuous memory ignition and misfire DTCs before any KOER HO2S DTCs.

Key in OFF position.
Visually inspect for:
- pinched, shorted, and corroded wiring and pins
- oil or water contamination
- crossed sensor wires
- contaminated or damaged sensor
Is a concern present?

Yes	No
REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test.	For KOER DTCs P2270, P2271, P2272, P2273, P2274 or P2275, GO to H34. For continuous memory DTCs P2270, P2271, P2272, P2273, P2274 or P2275, GO to H33.

H33 CHECK FOR KOER DTCS

Key ON, engine OFF.
Clear the DTCs.
Key ON, engine running.
Run the engine at approximately 2,000 RPM. Maintain the engine speed for 3 minutes.
Retrieve the continuous memory DTCs.
Are DTCs P2270, P2271, P2272, P2273, P2274 or P2275 present?

Yes	No
GO to H34.	Unable to duplicate or identify the concern at this time. refer to PINPOINT TEST Z .

H34 CHECK THE HO2S SIGNAL LEVEL TOO HIGH

NOTE: Fuel calculations can be affected by unmetered air leaks.

Key in OFF position.
Carefully inspect the following areas for potential air leaks:
- hoses connecting to the mass air flow (MAF) sensor assembly
- hoses connecting to the throttle body
- intake manifold gasket leaks
- PCV system
- the vacuum lines are disconnected
- improperly seated engine oil dipstick, tube or oil fill cap
- exhaust leaks at flanges and gaskets
With the vehicle in NEUTRAL, position it on a hoist. Refer to the appropriate JACKING AND LIFTING article for the locations of the lifting points.
Visually inspect for:
- exhaust leaks at flanges and gaskets
- HO2S not tightened to specification
- physical exhaust system concerns
- aftermarket exhaust
- punctures or cracks in the catalyst
Is a concern present?

Yes	No
REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test.	GO to H35.

H35 CHECK FOR SHORTS BETWEEN CIRCUITS IN THE HO2S HARNESS

PCM connector disconnected.
Disconnect the HO2S harness connector.

Measure the resistance between:

( + ) PCM Connector, Harness Side	( - ) Vehicle Battery
HO2S Signal	Negative terminal

Measure the resistance between:

( + ) PCM Connector, Harness Side	( - ) PCM Connector, Harness Side
HO2S Signal	SIGRTN
HO2S Signal	VPWR
HO2S Signal	HO2S Heater

Are the resistances greater than 10K ohms?

Yes	No
GO to H36.	REPAIR the short circuit. CLEAR the DTCs. REPEAT the self-test.

H36 CHECK THE HO2S CIRCUIT FOR AN OPEN IN THE HARNESS

Measure the resistance between:

( + ) PCM Connector, Harness Side	( - ) HO2S Connector, Harness Side
HO2S Heater	HO2S Heater
VPWR	VPWR
HO2S Signal	HO2S Signal
SIGRTN	SIGRTN

Are the resistances less than 5 ohms?

Yes	No
GO to H37.	REPAIR the open circuit. CLEAR the DTCs. REPEAT the self-test.

H37 CHECK THE HO2S CIRCUIT VOLTAGE

PCM connector connected.
HO2S connector connected.
Key ON, engine running.
Access the PCM and monitor the HO2S Signal PID.
Is the voltage greater than 1.5 V?

Yes	No
For partial zero emission vehicle (PZEV), GO to H40. For all others, GO to H39.	GO to H38.

H38 CHECK THE HO2S CIRCUIT VOLTAGE

Key in OFF position.
PCM connector connected.
HO2S connector disconnected.

Connect a 5 amp fused jumper wire between the following:

Point A HO2S Connector, Harness Side	Point B HO2S Connector, Harness Side
HO2S Signal	VPWR

Key ON, engine OFF.
Access the PCM and monitor the HO2S Signal PID.
Is the voltage greater than 1.5 V?

Yes	No
INSTALL a new HO2S. REFER to the appropriate ELECTRONIC ENGINE CONTROLS article. RESET the keep alive memory (KAM). REFER to RESETTING THE KEEP ALIVE MEMORY (KAM) . REPEAT the self-test.	GO to H42.

H39 CHECK FOR OVER VOLTAGE IN THE PCM

Key in OFF position.
HO2S connector disconnected.
Key ON, engine OFF.

Measure the voltage between:

( + ) HO2S Connector, Harness Side	( - ) Vehicle Battery
SIGRTN	Negative terminal
HO2S Signal	Negative terminal

Are the voltages less than 1.5 V?

Yes	No
INSTALL a new HO2S. REFER to the appropriate ELECTRONIC ENGINE CONTROLS article. RESET the keep alive memory (KAM). REFER to RESETTING THE KEEP ALIVE MEMORY (KAM) . REPEAT the self-test.	GO to H42.

H40 CHECK THE HO2S CIRCUIT FOR A SHORT TO VPWR IN THE HARNESS

Key in OFF position.
PCM connector disconnected.
HO2S connector disconnected.

Measure the resistance between:

( + ) PCM Connector, Harness Side	( - ) HO2S Connector, Harness Side
HO2S Signal	VPWR

Is the resistance greater than 10K ohms?

Yes	No
GO to H41.	REPAIR the short circuit. CLEAR the DTCs. REPEAT the self-test.

H41 CHECK THE HO2S CIRCUIT VOLTAGE

PCM connector connected.
HO2S connector disconnected.

Connect a 5 amp fused jumper wire between the following:

Point A HO2S Connector, Harness Side	Point B HO2S Connector, Harness Side
HO2S Signal	VPWR

Key ON, engine running.
Access the PCM and monitor the HO2S Signal PID.
Is the voltage greater than 1.5 V?

Yes	No
INSTALL a new HO2S. REFER to the appropriate ELECTRONIC ENGINE CONTROLS article. RESET the keep alive memory (KAM). REFER to RESETTING THE KEEP ALIVE MEMORY (KAM) . REPEAT the self-test.	GO to H42.

H42 CHECK FOR CORRECT PCM OPERATION

Disconnect all the PCM connectors.
Visually inspect for:
- pushed out pins
- corrosion
Connect all the PCM connectors and make sure they seat correctly.
Carry out the PCM self-test and verify the concern is still present.
Is the concern still present?

Yes	No
INSTALL a new PCM. REFER to FLASH ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY (EEPROM) .	The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.