REVISED TECH 1 MASS STORAGE CARTRIDGE (MSC) OXYGEN SENSOR. Buick Century 1995

REVISION: 01/18/96

THIS BULLETIN IS BEING REVISED TO MODIFY THE TEXT AND THE ART. THIS BULLETIN CANCELS AND SUPERSEDES BULLETIN 316520. *********************************************************************

SUBJECT: REVISED TECH 1 MASS STORAGE CARTRIDGE (MSC) OXYGEN SENSOR TEST

MODELS: 1995 AND PRIOR PASSENGER CARS AND TRUCKS, ALL GASOLINE CARBURETED, TBI, MFI, AND CMFI

**GENERAL INFORMATION** THE '95/'94 MSC O2S TEST FOR PASSENGER AND TRUCK APPLICATIONS IS AVAILABLE WITH THE JULY CD-ROM RELEASE OF THE MSC POWERTRAIN APPLICATION SOFTWARE.

THE 95/'94 O2S TEST RELEASED WITH THE JULY CD-ROM PROVIDES BOTH A HEATER CIRCUIT TEST AND A RICH/LEAN MEAN (AVERAGE) VOLTAGE TEST. THIS TEST IS AVAILABLE UNDER THE POWERTRAIN "MISC. TESTS" MENU ONCE THE "MODEL YEAR," "ENGINE," AND "VEHICLE" INFORMATION IS ENTERED.

THE O2S HEATER CIRCUIT TEST IS NOT SUPPORTED FOR THE FOLLOWING APPLICATIONS:

'94/'95 3.1L RPO L82, A-CAR '94/'95 3.4L RPO LQ1, W-CAR

THE O2S HEATER CIRCUIT TEST IS MODIFIED ON THE FOLLOWING APPLICATIONS:

'94/'95 4.6L RPO L37, E/K-CAR AND K SPECIAL '95 4.0L RPO L47, G-CAR

ONCE THE VEHICLE INFORMATION IS ENTERED, YOU ARE ASKED THE QUESTION "RUN HEATER ELEMENT CIRCUIT(S) TEST?". AFTER ANSWERING YES, THE SCREEN "WAITING FOR ECT TO COOL DOWN TO 100 DEGREES C", WILL APPEAR. AT THIS POINT YOU PRESS ENTER AND PROCEED WITH TEST AS USUAL.

THE '81 TO '95 MSC 02S TEST FOR PASSENGER AND TRUCK APPLICATIONS IS AVAILABLE WITH THE AUGUST CD-ROM RELEASE OF THE MSC POWERTRAIN APPLICATION SOFTWARE.

**PURPOSE** THE MSC O2S TEST IS USED TO VERIFY PROPER HEATER OPERATION ON VEHICLES EQUIPPED WITH HEATED OXYGEN SENSORS (HO2S). THE O2S TEST IS ALSO USED TO VERIFY PROPER O2S VOLTAGE RESPONSE DURING PART THROTTLE OPERATION AT A STEADY 2000 RPM ENGINE SPEED. REFER TO THE APPLICABLE DIAGNOSTIC PROCEDURES IN THE VEHICLE SERVICE MANUAL SHOULD EITHER PORTION OF THE O2S TEST INDICATE ABNORMAL O2S PERFORMANCE.

**DESCRIPTION** THE O2S TEST ACTUALLY CONSISTS OF TWO INDIVIDUAL TESTS: A HEATER CIRCUIT TEST AND THE RICH/LEAN MEAN VOLTAGE TEST. THE TESTS MAY BE PERFORMED IN SERIES OR INDIVIDUALLY AS REQUIRED.

1. ENTER THE VEHICLE SPECIFIC INFORMATION AND THEN SELECT "O2S SYSTEM" UNDER THE "MISC. TESTS" MENU.

2. THE TECH 1 DISPLAYS ANY DTCS THAT ARE PRESENT AND PROMPTS YOU TO PRESS "YES" TO CONTINUE WITH THE TEST. DTCS ASSOCIATED WITH EITHER THE O2S OR FUEL TRIM FUNCTION SHOULD BE DIAGNOSED BEFORE CONTINUING WITH THE TEST.

3. DETERMINE IF THE VEHICLE HAS A HEATED O2S. AT THE PROMPT "IS VEHICLE EQUIPPED WITH A HEATED O2 SENSOR?" PRESS "YES" OR "NO" AS APPLICABLE. SELECT "YES" AT THE PROMPT "RUN HEATER ELEMENT CIRCUIT TEST?" TO RUN THE HEATER CIRCUIT TEST. NON-HEATED SENSORS WILL APPEAR AS FAILURES IF TESTED.

4. AT THE PROMPT "HEATER ELEMENT CIRCUIT TEST COMPLETE," PRESS THE UP ARROW TO DISPLAY THE TEST RESULTS. AFTER REVIEWING THE HEATER ELEMENT TEST RESULTS, PRESS THE UP ARROW TO DISPLAY THE PROMPT "CONTINUE TEST? YES/NO." PRESS "NO" TO EXIT THE TEST OR PRESS "YES" TO CONTINUE WITH THE MEAN VOLTAGE TEST.

A FAILURE OF THE HEATER CIRCUIT TEST DOES NOT NECESSARILY INDICATE A BAD O2S. CHECK THE HEATER VOLTAGE AND GROUND CIRCUITS USING THE APPLICABLE VEHICLE SERVICE MANUAL. IF THESE CIRCUITS ARE OK, REPLACE THE O2S.

5. THE PROMPT "MEAN (AVERAGE) VOLTAGE TEST SET UP, ACCESS, A/C, AIR OFF" ALERTS YOU TO PREPARE THE VEHICLE FOR THE RICH/LEAN MEAN VOLTAGE TEST. MAKE SURE THAT ALL ACCESSORIES AND THE AIR CONDITIONING ARE TURNED OFF. DISABLE THE SECONDARY AIR INJECTION IF SO EQUIPPED.

6. AT THE PROMPT "RAISE RPM TO 2500" INCREASE THE ENGINE SPEED TO 2500 RPM AND HOLD. THE TECH 1 INITIATES A ONE MINUTE PRECONDITIONING TIMER. THIS PRECONDITIONING PHASE IS USED TO HEAT THE SENSOR PRIOR TO RUNNING THE RICH/LEAN MEAN VOLTAGE TEST.

IF O2S VOLTAGE DID NOT SWING A MINIMUM OF 100 MV IN BOTH DIRECTIONS, THE PROMPT "O2S VOLTAGE DID NOT TOGGLE DURING PRECONDITIONING" IS DISPLAYED AFTER THE ONE MINUTE PRECONDITIONING PHASE. CHECK THE O2S REFERENCE AND GROUND CIRCUITS FOLLOWING THE PROCEDURES OUTLINED IN THE APPLICABLE SERVICE MANUAL. IF THE CIRCUITS ARE OK, REPLACE THE SENSOR.

7. AT THE PROMPT "DECREASE AND HOLD AT 2000 RPM," LOWER ENGINE SPEED TO 2000 RPM. WHEN ENGINE SPEED IS STEADY AT 2000 RPM (+/- 160 RPM) THE TECH 1 DISPLAYS THE PROMPT "HOLD AT 2000 RPM, PROCESSING DATA." THE TECH 1 BEGINS CAPTURING O2S VOLTAGE SAMPLES.

WHEN THE REQUIRED NUMBER OF SAMPLES ARE OBTAINED, THE TECH 1 DISPLAYS THE PROMPT "TEST COMPLETE." PRESS THE UP ARROW TO DISPLAY THE TEST RESULTS SCREEN.

8. THE TECH 1 FIRST REPEATS THE RESULTS OF THE HEATER ELEMENT CIRCUIT TEST (IF RUN). PRESS THE UP ARROW TO DISPLAY THE LIMITS FOR THE MEAN HIGH (RICH) VOLTAGE AND THE ACTUAL MEAN HIGH VOLTAGE CALCULATED DURING THE TEST. PRESS THE UP ARROW AGAIN TO SCROLL TO THE NEXT SCREEN. THE TECH 1 THEN DISPLAYS THE LIMITS FOR THE MEAN LOW (LEAN) VOLTAGE AND THE ACTUAL MEAN LOW VOLTAGE CALCULATED DURING THE TEST.

IF BOTH THE HIGH AND LOW MEAN VOLTAGES ARE WITHIN THE SPECIFIED RANGE, THE O2S IS SWITCHING THROUGH ITS FULL RANGE INDICATING CORRECT PERFORMANCE OF THE SENSOR, ITS CIRCUITRY AND ECM/PCM CLOSED LOOP FUEL CONTROL. THIS IS ILLUSTRATED IN FIGURE 1, EXAMPLE A. EXAMPLE B OF FIGURE 1 SHOWS AN O2S WAVEFORM WITH A LIMITED SIGNAL RANGE. THERE ARE SOME VOLTAGE SAMPLES WITHIN THE HIGH AND LOW MEAN LIMITS BUT THE MAJORITY OF SAMPLES FAIL TO REACH EITHER LIMIT.

A MEAN HIGH VOLTAGE BELOW THE 600 MV LIMIT IS TYPICALLY A RESULT OF THE FOLLOWING:

* CARBON FOULED SENSOR (TEMPORARY POISONING) * RESISTANCE IN THE O2S CIRCUIT * EXHAUST LEAK * WATER INTRUSION

A MEAN LOW VOLTAGE ABOVE THE 300 MV LIMIT IS TYPICALLY A RESULT OF THE FOLLOWING:

* SILICA OR LEAD FOULED SENSOR (PERMANENT POISONING) * POOR CONNECTION OR AN OPEN ON THE O2S SIGNAL LOW (GROUND)

**O2S TEST MESSAGES**

**"LOW O2S ACTIVITY. SEE I/M SERVICE INFORMATION AND BULLETINS"** THIS MESSAGE SIGNALS THAT THERE WERE FEWER THAN TEN RECORDED O2S VOLTAGE SAMPLES ON EITHER THE RICH ()450 MV) SIDE OR THE LEAN ((450 MV) SIDE. THIS RESULT DOES NOT ALWAYS INDICATE A DEGRADED SENSOR. THERE ARE SOME APPLICATIONS (FOR EXAMPLE THE '88/'89 5.0/5.7L TBI TRUCK) THAT COMMAND O2S VOLTAGE UNDER 150 MV DURING HIGH RPM AND LOW LOAD CONDITIONS LIKE THOSE EXISTING DURING THE O2S TEST. THIS IS A NORMAL RESPONSE FOR VEHICLES WITH THIS PARTICULAR CALIBRATION.

TO DETERMINE IF YOUR VEHICLE HAS THIS FUEL CONTROL CALIBRATION, HOLD ENGINE SPEED AT 2000 RPM WHILE MONITORING O2 VOLTAGE AND SHORT TERM FUEL TRIM. IF THE VEHICLE HAS THIS CALIBRATION, THE SHORT TERM FUEL TRIM WILL BE FIXED AT 128 WHILE THE O2S VOLTAGE REMAINS LOW((150 MV). ON SOME APPLICATIONS, IT MAY BE NECESSARY TO PERFORM THE MEAN VOLTAGE TEST AT IDLE. IF YOU CHOOSE NOT TO RUN THE IDLE TEST, YOU MAY DRIVE THE VEHICLE AND RUN THE TEST AT A STEADY STATE CRUISE (APPROXIMATELY 55 MPH). CAUTION: TESTING THE VEHICLE AT A STEADY STATE CRUISE WILL REQUIRE TWO TECHNICIANS, ONE TO READ THE SCAN DATA AND ONE TO DRIVE THE VEHICLE.

THE IDLE TEST CONSISTS OF PERFORMING THE MEAN AVERAGE VOLTAGE TEST SET UP AND PRECONDITIONING AS PROMPTED BY THE TECH 1. AT THE PROMPT "DECREASE AND HOLD AT 2000 RPM FOR NEXT TEST", HOLD AT 2000 RPM (+/- 160 RPM) LONG ENOUGH FOR DATA SAMPLES TO START COUNTING. WHEN SAMPLES START, IMMEDIATELY DROP THE ENGINE RPM TO IDLE UNTIL THE REQUIRED NUMBER OF SAMPLES ARE OBTAINED. WHEN THE TECH 1 DISPLAYS THE PROMPT "TEST COMPLETE", PRESS THE UP ARROW TO DISPLAY THE TEST RESULT SCREENS.

**O2S VOLTAGE DID NOT TOGGLE DURING PRECONDITIONING"** THIS MESSAGE SIGNALS THAT THE O2S VOLTAGE DID NOT SWING A MINIMUM OF 100 MV IN BOTH DIRECTIONS DURING THE ONE MINUTE PRECONDITIONING PHASE. CHECK THE O2S REFERENCE AND GROUND CIRCUITS FOLLOWING THE PROCEDURES OUTLINED IN THE APPLICABLE SERVICE MANUAL. IF THE CIRCUITS ARE OK, REPLACE THE SENSOR.

THERE ARE SOME APPLICATIONS (FOR EXAMPLE THE '88/'89 5.0/5.7L TBI TRUCK) THAT COMMAND O2S VOLTAGE UNDER 150 MV DURING HIGH RPM AND LOW LOAD CONDITIONS LIKE THOSE EXISTING DURING THE O2S TEST. THIS IS A NORMAL RESPONSE FOR VEHICLES WITH THIS PARTICULAR CALIBRATION. ON SOME APPLICATIONS, IT MAY BE NECESSARY TO PERFORM THE MEAN VOLTAGE TEST AT IDLE. IF YOU CHOOSE NOT TO RUN THE IDLE TEST, YOU MAY DRIVE THE VEHICLE AND RUN THE TEST AT A STEADY STATE CRUISE (APPROXIMATELY 55 MPH). CAUTION: TESTING THE VEHICLE AT A STEADY STATE CRUISE WILL REQUIRE TWO TECHNICIANS, ONE TO READ THE SCAN DATA AND ONE TO DRIVE THE VEHICLE.

THE IDLE TEST CONSISTS OF PERFORMING THE MEAN AVERAGE VOLTAGE TEST SET UP AND PRECONDITIONING AS PROMPTED BY THE TECH 1. AT THE PROMPT "DECREASE AND HOLD AT 2000 RPM FOR NEXT TEXT", HOLD AT 2000 RPM (+/- 160 RPM) LONG ENOUGH FOR DATA SAMPLES TO START COUNTING. WHEN SAMPLES START, IMMEDIATELY DROP THE ENGINE RPM TO IDLE UNTIL THE REQUIRED NUMBER OF SAMPLES ARE OBTAINED. WHEN THE TECH 1 DISPLAYS THE PROMPT "TEST COMPLETE", PRESS THE UP ARROW TO DISPLAY THE TEST RESULT SCREENS.

**"O2S VOLTAGE SWING HIGH LIMITS )9. ACTUAL_."** THIS MESSAGE INDICATES THE ACTUAL NUMBER OF RECORDED O2S VOLTAGE SAMPLES ABOVE THE 450 MV REFERENCE LEVEL. A MEAN HIGH VOLTAGE IS NOT CALCULATED IF THERE ARE FEWER THAN TEN RECORDED O2S VOLTAGE SAMPLES ABOVE 450 MV. THIS RESULT DOES NOT ALWAYS INDICATE A DEGRADED SENSOR. REFER TO THE APPLICABLE VEHICLE SERVICE MANUAL FOR INFORMATION ON DIAGNOSING A LEAN AIR/FUEL MIXTURE.

**"O2S VOLTAGE SWING LOW LIMITS )9. ACTUAL _."** THIS MESSAGE INDICATES THE ACTUAL NUMBER OF RECORDED O2S VOLTAGE SAMPLES BELOW THE 450 MV REFERENCE LEVEL. A MEAN LOW VOLTAGE IS NOT CALCULATED IF THERE ARE FEWER THAN TEN RECORDED O2S VOLTAGE SAMPLES BELOW 450 MV. THIS RESULT DOES NOT ALWAYS INDICATE A DEGRADED SENSOR. REFER TO THE APPLICABLE VEHICLE SERVICE MANUAL FOR INFORMATION ON DIAGNOSING A RICH AIR/FUEL MIXTURE.

**"TEST ENDED COOLANT TOO HOT 120 DEGREES C"** THIS MESSAGE SIGNALS THAT THE ENGINE COOLANT TEMPERATURE IS TOO HIGH TO RUN THE O2S TEST. THE TEST WILL AUTOMATICALLY CONTINUE ONCE ECT FALLS BELOW 120 DEGREES C.

**"WAITING FOR CLOSED LOOP TO BE ACHIEVED"** THIS MESSAGE SIGNALS THAT THE TECH 1 IS WAITING FOR THE FUEL CONTROL SYSTEM TO ENTER CLOSED LOOP BEFORE RUNNING THE O2S TEST. THE TEST WILL AUTOMATICALLY CONTINUE ONCE THE SYSTEM ENTERS CLOSED LOOP OPERATION.

**"WAITING FOR ECT TO WARM UP TO 85 DEGREES C"** THIS MESSAGE SIGNALS THAT THE TECH 1 IS WAITING FOR ENGINE COOLANT TO REACH NORMAL OPERATING TEMPERATURE. THE TEST WILL AUTOMATICALLY CONTINUE ONCE ENGINE COOLANT REACHES 85 DEGREES C.

FIGURES: 01 ATTACHMENTS: 00

Object Number: 82743 Size: FS

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