Ccc Efi Tests W/o Codes Chevrolet Corsica I

TROUBLE SHOOTING

Note. This article does not apply to Reatta, Riviera and Toronado 3.8L PFI-equipped vehicles. For information on these vehicles, see appropriate articles.

HOW TO USE THIS ARTICLE

This article is to be used only AFTER you have checked the following

1. Verify the on-car diagnostics are working by performing appropriate DIAGNOSTIC CIRCUIT CHECK chart for that system.
2. Verify that the ECM and "SERVICE ENGINE SOON" light are functioning properly.
3. Verify that there are no trouble codes stored, or only intermittent ones.
4. Verify that the fuel control system is operating properly by performing appropriate FIELD SERVICE MODE CHECK.
5. Perform FUEL SYSTEM PRESSURE TEST on EFI vehicles.
6. Perform a careful visual inspection of all systems.

After all checks have been performed, verify customer complaint and locate correct symptom. Check items indicated under that symptom. Not all items listed under each symptom apply to all models and systems. These procedures will normally lead you to a component system on vehicle, such as EGR, EST, TCC, etc. These are covered in component system charts. These charts are listed with a "C" before the number of the chart (C-1A, for example).

FUEL SYSTEM PRESSURE TEST (EFI MODELS)

Note. Trouble shooting and diagnosis of fuel system should begin with determining fuel injection system pressure. Before replacing fuel system components, or installing fuel pressure gauge on TBI systems, fuel pressure must be relieved from system.

Throttle Body

1. On vehicles equipped with model 220 or 700 throttle body units, disconnect negative battery cable. Remove fuel filler cap. Since these TBI units contain an internal TBI bleed-down feature, after a short time, system fuel pressure should dissipate.
2. Remove air cleaner and plug thermal vacuum port on throttle body. When removing fuel line, always use 2 wrenches. Install Fuel Pressure Gauge (J-29658B or BT-8205 ) and Adapter (29658-85 ) in fuel line between steel line and flexible hose.
3. Start engine and observe fuel pressure reading. Fuel pressure should read 9-13 psi (.6-.9 kg/cm 2 ). If fuel pressure is okay, proceed to step 4). If fuel pressure is not correct, see appropriate CHART A-7, FUEL SYSTEM DIAGNOSIS for that system.
4. Allow fuel pressure to dissipate as described in step 1). Remove fuel pressure gauge and reconnect fuel line. Start engine and watch for fuel system leaks. For further details on fuel pressure testing, proceed to appropriate CHART A-7 for that system.

Note. Trouble shooting and diagnosis of fuel system should begin with determining fuel injection system pressure. Before replacing fuel system components on PFI systems, fuel pressure must be relieved from system.

Port Injection

1. Connect Fuel Pressure Gauge (J-34730-1) to fuel pressure connector in fuel rail. To reduce possibility of fuel spillage and possible fire hazard, wrap shop cloth around fitting while connecting or disconnecting gauge.
2. To bleed pressure from system for component replacement, insert bleed hose into an appropriate container and open gauge valve.
3. With gauge installed at fuel rail connector, turn ignition on. With ignition on and engine off, pressure should read 40-47 psi (2.8-3.3 kg/cm 2 ). Start engine. Pressure should drop 3-10 psi (.2-7 kg/cm 2 ). For further details on fuel system pressure testing, proceed to appropriate CHART A-7 for that system.

Symptom Definition

"SERVICE ENGINE SOON" light comes on but does not stay on. A stored code may or may not exist.

Possible Cause & Correction

To track down possible causes of an intermittent "SERVICE ENGINE SOON" light check the following items.

1. Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire to terminal connections.
2. Check for poor connection from ignition coil to ground or arcing at spark plug wires or plugs.
3. Check wire from "SERVICE ENGINE SOON" light to ECM for short to ground.
4. Check wire from ALDL "test" terminal for intermittent short to ground.
5. Check for poor connections in ECM ground terminals.
6. Check for loss of trouble code memory. To check code memory on fuel injected models, disconnect TPS and run engine at idle until "SERVICE ENGINE SOON" light comes on. Code 22 should be stored and retained in memory when ignition is turned off.
7. Check for electrical system interference caused by a defective relay or an ECM driven solenoid or switch which may cause a sharp electrical surge. This type of problem will normally occur when faulty component is operated.
8. Check for aftermarket parts which may not have been produced to manufacturers' specifications. Solenoids without original equipment diodes for circuit protection and HEI-EST module or voltage regulator using transistors instead of silicon-chip circuitry may possibly cause voltage surges (up to 300 volts) in ECM wiring, causing temporary ECM shutdown. ECM shutdown is a normal response to system overvoltage (over 16 volts on most models). ECM will repower when condition ceases to exist. This could cause a flickering "SERVICE ENGINE SOON" light with no codes set in memory.
9. Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
10. Make sure that EST wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and generator. Make sure that ground wire from ECM to distributor or ignition module is connected to a good ground.
11. Check for intermittent short to ground on terminals "B" (diagnostic enable) or "D" ("SERVICE ENGINE SOON" light) at ALDL.
12. Check for intermittent wiring problem using "Scan" tester. See SCAN TESTER USAGE in TROUBLE SHOOTING section of this article.

Engine cranks okay, but does not start for a long time. Engine eventually starts, may immediately die or run okay.

Check the following items

1. Check fuel pump relay. (Except Corvette) To do this, connect test light between fuel pump test terminal (terminal "G" of ALDL on most vehicles) and ground. Turn ignition on. Light should illuminate for 2 seconds. If not, see appropriate CHART A-5, FUEL PUMP RELAY CIRCUIT for that system.
2. Check for poor quality or water contaminated fuel.
3. Check that TPS is not sticking or binding.
4. Check EGR operation. See appropriate component CHART C-7 for that system.
5. Check for a leaking injector. To do this on TBI systems, disconnect injector electrical connector at injector. Crank engine and watch for fuel leakage.
6. Check that resistance of coolant sensor circuit or coolant sensor is not too high. See CODE 15 chart.
7. Check ignition system for a worn distributor shaft, bare or shorted wires, incorrect pick-up coil resistance, loose ignition coil ground or moisture in distributor cap. Check for adequate spark using Spark Tester (ST-125 ).
8. Check for shorts by spraying plug wires with a fine mist of water.
9. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
10. Check for correct fuel pressure in all speed ranges. See appropriate CHART A-7 for that system.
11. A faulty in-tank fuel pump check valve will allow fuel in lines to drain back to tank after engine is stopped. To check this condition, turn ignition off, disconnect fuel pressure line at fuel rail, remove filler cap, and connect a radiator test pump and apply 15 psi (1.0 kg/cm 2 ) pressure. If pressure will hold for 60 seconds, check valve is okay.
12. Check that PROM in vehicle is correct for that vehicle. Check with dealer for latest application information.
13. Check for restricted exhaust system.

Engine starts okay but dies after brief idle, dies as soon as any load is placed on engine (such as turning on air conditioner or engaging transmission), or on initial driveaway.

Check the following items

1. Make sure that hot air tube is connected to air cleaner.
2. Check for proper operation of thermostatic air cleaner.
3. Check for proper operation of Idle Air Control (IAC) system. See appropriate component CHART C-2 for that system.
4. Check PCV valve for proper operation.
5. Unplug MAF sensor (if equipped). ECM will substitute a default value for MAF signal. If stall condition is eliminated, replace MAF sensor.
6. Check EGR system for proper operation. See appropriate component CHART C-7 for that system.
7. If stall occurs when air conditioner is turned on, check for air conditioner clutch signal to ECM terminal. Voltage at A/C terminal of ECM should be battery voltage when air conditioner compressor clutch is engaged. A high voltage surge due to a shorted compressor clutch diode could cause ECM shutdown.
8. Check for an overcharged air conditioner system.
9. Check for plugged or restricted fuel lines. See appropriate component CHART A-7, FUEL SYSTEM DIAGNOSIS for that system.
10. Using Spark Tester (ST-125 ), check for a weak spark from ignition coil.

Momentary lack of response when accelerator is pushed down. Can occur at all vehicle speeds. Usually occurs when taking off from a stop.

Check the following items

1. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
2. Check wires for pinches, cuts, and proper connections.
3. Check that fuel pressure is correct in all speed ranges. See appropriate CHART A-7, FUEL SYSTEM DIAGNOSIS for that system. Also check for poor quality or water contaminated fuel.
4. Check for fouled spark plugs.
5. Check that PROM in vehicle is correct for that vehicle. Check with dealer for latest application information.
6. Check for a binding or sticking TPS.
7. Make sure that initial ignition timing is properly set.
8. Make sure that ECM controlled idle speed is correct.
9. Check EGR system for proper operation. See appropriate component CHART C-7 for that system.
10. Disconnect fuel injector electrical connectors. Crank engine and check for injector leaks.
11. Check for an open in HEI ground circuit.
12. Check canister purge system for proper operation.
13. Check charging system output. Repair charging system if voltage is less than 9 volts or more than 16 volts.
14. Perform injector balance test (PFI). See appropriate component CHART C-2A for that system.

Engine power varies under steady throttle or cruise. Feels like vehicle speeds up and slows down without changing position of accelerator pedal.

Check the following items

1. Perform DIAGNOSTIC CIRCUIT CHECK. Perform SYSTEM PERFORMANCE CHECK for 5.0L (VIN Y) engines.
2. Check operation of thermostatic air cleaner damper door.
3. Check that Park/Neutral switch is properly adjusted. See appropriate component CHART C-1A.
4. Check for intermittent open or short to ground in Torque Converter Clutch (TCC) or HEI by-pass circuits. See appropriate component CHART C-8, TORQUE CONVERTER CLUTCH or appropriate component CHART C-4, HEI-EST CHECK for that system.
5. Check for proper operation of canister purge system. See appropriate component CHART C-3 for that system.
6. Check for proper operation of ESC system. See appropriate component CHART C-5 for that system.
7. Check for proper operation of EGR system. See appropriate component CHART C-7 for that system.
8. Make sure that initial ignition timing is properly set.
9. Check for adequate spark output using Spark Tester (ST-125).
10. Check O2 sensor for lead or RTV sealant contamination. This will cause a false high voltage signal to ECM. ECM will respond by leaning air/fuel ratio.
11. Check in-line fuel filter and replace if dirty or clogged.
12. Check fuel for water contamination. On EFI models, check that fuel system pressure is correct at all engine speeds. See appropriate CHART A-7, FUEL SYSTEM DIAGNOSIS for that system.
13. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits. Also check condition of distributor cap, rotor and spark plug wires.
14. Check A/C for excessive charge.
15. Check for restricted exhaust system.

Engine delivers less power than expected. Little or no increase in speed when accelerator is pushed down.

Check the following items

1. Perform DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system.
2. Check that air filter and fuel filter are not plugged. Replace if necessary. Check for incorrect fuel pressure. On EFI vehicles, see appropriate component CHART A-7 for that system.
3. Check for proper operation of thermostatic air cleaner damper door.
4. Make sure that initial ignition timing is properly set.
5. Check for proper operation of TCC system. See appropriate component CHART C-8 for that system.
6. Check ESC system for excessive retard. See appropriate component CHART C-5 for that system.
7. Check EST system for proper operation. See appropriate component CHART C-4 for that system.
8. Make sure that EGR valve is not open all the time. See appropriate component CHART C-7 for that system.
9. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B-1, RESTRICTED EXHAUST SYSTEM CHECK for that system.
10. Check charging system output. Repair charging system if voltage is less than 9 volts or more than 16 volts.
11. Check MAP or pressure sensor output. See appropriate component CHART C1-D for that system.
12. Using Spark Tester (ST-125), check for available secondary voltage.
13. Check engine valve timing and compression.
14. Check engine for a worn camshaft.

Fuel ignites in intake manifold or in exhaust system making a loud popping noise.

Check the following items

1. Check for proper valve timing.
2. Check engine for sticking or leaking valves.
3. Check for fuel or water in vacuum hose to MAP sensor. Also check for restricted hose.
4. Using Spark Tester (ST-125 ), check available output voltage of ignition coil.
5. Check for crossfire between spark plugs, distributor cap and spark plug wires.
6. Check for an intermittent ignition system problem.
7. Make sure that initial ignition timing is properly set.

Engine runs unevenly at idle. If bad enough vehicle will shake. Idle may vary in RPM. Engine idles at incorrect RPM.

Check the following items

1. Perform DIAGNOSTIC CIRCUIT CHECK. Perform SYSTEM PERFORMANCE CHECK for 5.0L (VIN Y) engines.
2. Make sure that throttle linkage and/or TPS are not sticking or binding.
3. Make sure that initial ignition timing is properly set.
4. Check engine idle speed, both base idle and ECM idle.
5. Check Idle Air Control (IAC) system. Check for foreign material in IAC bore. See DIAGNOSTIC AIDS in CODE 35 chart or appropriate component CHART C-2 for that system.
6. Check for proper operation of EGR system. See appropriate component CHART C-7 for that system.
7. Check ISC/ILC operation. See appropriate component CHART C-2 for that system.
8. Check P/N switch circuit. Also make sure that P/N switch is properly adjusted. See appropriate component CHART C-1.
9. Check power steering pressure switch circuit. See appropriate component CHART C-1 for that system.
10. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B-1, RESTRICTED EXHAUST SYSTEM CHECK for that system.
11. If rough idle only occurs when engine is hot, check PCV valve for proper operation, check evaporative emission control system, check for proper spark plug gap and check engine compression.

Engine starts but will not run at idle. Engine will run if accelerator is held at part throttle.

Check the following items

1. Problem is most likely in Idle Air Control (IAC) system. See DIAGNOSTIC AIDS in appropriate CODE 35 chart for that system.
2. Check EGR system. See appropriate component CHART C-7 for that system.
3. Check P/N switch. See appropriate component CHART C-1A for that system.
4. Check injector balance. See appropriate component CHART C-2 for that system.
5. Disconnect MAF sensor. If condition is corrected, replace sensor.

Fuel economy, as measured by an actual road test, is noticeably lower than expected. Fuel economy is noticeably lower than was on this vehicle at one time.

Check the following items

1. Check for proper operation of thermostatic air cleaner damper door. Also check for a clogged air filter.
2. Check cooling system thermostat for proper heat range and operation.
3. Check coolant sensor for shift in calibration. Use temperature-to-resistance chart in Code 14 or 15 chart.
4. Make sure that speedometer is properly calibrated.
5. Check engine compression.
6. Check for dragging brakes.
7. Check A/C for "full time" operation.
8. Make sure that initial ignition timing is properly set and check for proper EST and ESC operation. See appropriate component CHART C-4 and C-5 for that system.
9. Check for proper operation of Torque Converter Clutch (TCC). See appropriate component CHART C-8 for that system.
10. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B-1, RESTRICTED EXHAUST SYSTEM CHECK for that system.
11. Check oxygen sensor for silicone or lead contamination.
12. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
13. Make sure that speedometer is properly calibrated.
14. Check engine compression.
15. Check for dragging brakes.

Engine continues to run after ignition is turned off but runs very rough. If engine runs smoothly, check ignition switch.

Check the following items

1. Check for binding throttle linkage.
2. Check for leaking injectors on EFI vehicles. See appropriate component CHART A-7 for that system. On multi-point fuel injected systems, check injector balance. See appropriate component CHART C-2 for that system.
3. Check IAC system. See DIAGNOSTIC AIDS in appropriate CODE 35 chart or component CHART C-2 for that system.
4. Check ILC for proper operation. See appropriate component CHART C-2 for that system.
5. Check engine for overheating.

A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with amount of acceleration.

Check the following items

1. Check for obvious overheating problems.
2. Make sure that initial timing is correct.
3. Check TPS adjustment and operation.
4. On fuel injected models, check fuel system for low pressure or volume. See appropriate CHART A-7 for that system. Also check for induction air leaks.
5. Make sure that ESC system is operating properly. See appropriate component CHART C-5 for that system.
6. Make sure that EGR valve is not open all the time. See appropriate component CHART C-7 for that system.
7. Make sure that TCC system is operating properly. See appropriate component CHART C-8 for that system.
8. Make sure that correct PROM is installed in ECM.
9. Remove carbon from engine with top engine cleaner.
10. If excessive carbon exists in combustion chamber, check for excessive oil burning due to leaking valve guide seals.
11. Check for incorrect basic engine parts such as camshaft, cylinder heads and pistons.
12. Check that PROM in vehicle is correct for that vehicle. Check with dealer for latest application information.

Vehicle fails emission test. Vehicle may also have excessive "rotten egg" smell (hydrogen sulfide) being emitted from exhaust pipe.

Check the following items

1. Perform both DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system.
2. Check for lead contamination of catalytic converter. Look for removal/tampering at restrictor in fuel filler neck.
3. If emission test shows excessive carbon monoxide (CO) and hydrocarbons (HC) emissions and vehicle also has excessive odor being emitted, check all systems and components that could cause engine to run rich. See DIAGNOSTIC AIDS in appropriate CODE 45 chart for that system.
4. If emission test shows excessive oxides of nitrogen (NOx) emissions, check all systems and components that could cause engine to run lean or to run too hot. See DIAGNOSTIC AIDS in appropriate CODE 44 chart for that system.

Cuts out, misses is defined as a steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. The exhaust may have a steady spitting sound at idle or low speed.

Check the following items

1. Check ignition wires for short or faulty insulation.
2. Check Distributor cap (if equipped) for moisture, dust or cracks. Spray spark plug wires with a fine mist of water to check for shorts.
3. Connect Spark Tester ST-125 to spark plug and check for adequate spark.
4. Check ignition system for faulty grounds.
5. Check that EST wiring harness is not routed too close to wiring which may cause induced voltage signals.
6. Check ignition coil connections.
7. Remove spark plugs and check for correct heat range, wear, cracks, wetness, improper gap or heavy deposits.
8. Check for poor or contaminated (water) fuel.
9. Check for improper fuel pressure.
10. Check float level on carbureted vehicles.
11. Perform a INJECTOR BALANCE TEST, check fuel injected vehicles for plugged injectors.
12. Check for EGR valve sticking open.
13. Check ECM for proper ground circuits.
14. TPS for sticking or binding. TPS voltage should be less than 1.25 volts at idle.
15. Check for proper crank angle sensor (DIS and IDI) or pick-up coil (HEI distributor) resistance.
16. Check for restricted exhaust.
17. Check for bent push rods, broken valve springs or worn camshaft lobes.

SCAN TESTER USAGE

Note. Prior to connection of scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received by scan tester will be accurate. This is done by performing appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If vehicle does not pass diagnostic circuit check, information received by scan tester may be invalid.

CCC Scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to back-probe sensors and connectors. Scan testers cut down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters (see SCAN DATA tables). They also furnish information on output device (solenoids and motors) status. Status parameters, however, are only an indication that output signals have been sent to devices by the ECM. It does not indicate if devices have responded properly to that signal. This will need to be verified at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine not running but may not be indicated by all makes of scan testers.

If trouble codes are not present, this is not an indication that there is not a problem. CCC related problems are about 20 percent codes and 80 percent driveability. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Use of a scan tester is easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN DATA tables in this section.

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, it will be necessary to verify tester information using a digital voltmeter and wiring schematic. If non- existent codes are in evidence, turn ignition off, remove tester, turn ignition on and ground ALDL "test" terminal. If same codes are not flashed by "SERVICE ENGINE SOON" light that were indicated by scan tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate.

THROTTLE BODY INJECTION - SCAN DATA SPECIFICATIONS

Note. Information contained in the following table is typical of readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are virtually instantaneous. Not all devices & systems are used on all models.

THROTTLE BODY INJECTION

PORT FUEL INJECTION - SCAN DATA SPECIFICATIONS

Note. Information contained in the following table is typical of readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are virtually instantaneous. Not all devices & systems are used on all models.

PORT FUEL INJECTION

PRECAUTIONS

STATIC CHARGE (VOLTS)

Servicing ECM Using 3M Anti-Static Mat. Scheme 186

ELECTRONIC CONTROL MODULE (ECM)

Note. Prior to replacement of ECM, a careful inspection of all wiring and control components should be made. Failure to test for shorts, grounds and reasons for Quad-Driver failure may cause repeat failure of ECM. To prevent internal damage to ECM, ignition switch must be in "OFF" position when disconnecting or reconnecting ECM connectors or 12-volt components.

Removal

Turn ignition switch to "OFF" position. Disconnect negative battery cable from battery. Locate ECM and remove access panels, if any. Remove electrical connectors from ECM. Remove ECM from vehicle. Remove MEM-CAL or PROM and CALPAC (if equipped) from ECM.

Installation

Install PROM and CALPAC (if equipped) or MEM-CAL in new ECM. Reinstall ECM into vehicle. Reconnect electrical connectors to ECM. Install access panels. Reconnect negative battery cable to battery.

1. Remove ECM from vehicle as previously described. Position ECM so that bottom cover is facing upward. Remove slide-off PROM access cover by depressing locking tab.
2. Using PROM removal tool, grasp PROM at narrow ends. Gently rock PROM from end to end while pulling up. If new PROM is to be installed, remove old PROM from PROM carrier.

Note. Note location of reference notches in PROM, carrier and ECM for reassembly reference.

1. Check that new PROM has same service number as old one. Place new PROM in PROM carrier. Position squarely over ECM PROM socket. Press on PROM carrier until PROM is firmly seated in ECM. NOTE: Make sure that reference notches in both ECM and PROM are properly aligned. If PROM is installed backwards and key is turned on, PROM will be destroyed.
2. Reinstall PROM access cover on ECM. Reinstall ECM in vehicle as previously described. Start engine and ground diagnostic test lead. Watch for trouble Code 51.
3. If this occurs, PROM is not fully seated in ECM, installed backwards, has bent pins or is defective. If pins are bent and crack when straightened, PROM must be replaced. If PROM is installed backwards or is defective, it must be replaced.

CALPAC

Some ECM models use a CALPAC as well as a PROM. (Scheme 187) The CALPAC must also be removed from replaced ECM and installed in new one. Removal and replacement procedures for CALPAC are same as for PROM. If units are installed improperly, grounding diagnostic test lead will set Code 52.

Scheme 187

Using 2 fingers, push retaining clips back from MEM-CAL. At same time, grasp it at both ends and lift up out of socket. DO NOT remove MEM-CAL cover.

Carefully align MEM-CAL pins with ECM pin holes. DO NOT press in middle of MEM-CAL. Push downward evenly on ends of MEM-CAL until retaining clips on ends of MEM-CAL snap into place.

Disconnect negative battery cable at battery. Raise vehicle on hoist. Disconnect electrical connector from oxygen sensor. Carefully remove oxygen sensor from exhaust pipe.

Note. Oxygen sensor may be difficult to remove when engine temperature is less than 120°F (49°C). Excessive removal force may damage threads in exhaust manifold or pipe.

1. Whenever an oxygen sensor is removed, its threads must be coated with anti-seize compound before it is reinstalled. New oxygen sensors will already have this compound applied to threads.
2. Install oxygen sensor in exhaust pipe and tighten sensor to 30 ft. lbs. (41 N.m). CAUTION: Correct torque of O2 sensor is critical to prevent crushing glass beads in graphite anti-seize compound. Crushing glass beads will cause sensor to seize in exhaust manifold, causing necessary replacement of exhaust manifold upon next removal attempt.
3. Reconnect electrical connector to oxygen sensor. Lower vehicle from hoist. Reconnect negative battery cable.

ALL OTHER SENSORS, SOLENOIDS & SWITCHES

Removal of all other sensors, switches and solenoids is accomplished by turning ignition off, removing electrical and/or vacuum connectors and removing or detaching component.

Computerized Engine Control Diagnostic Procedure. Scheme 188

Note. If ECM displays data but engine fails to start, proceed to chart A-3 in the TESTS W/CODES article in this section.

Note. Condensed, general SYMPTOM DIAGNOSIS and INTERMITTENTS articles are also located in the TROUBLE SHOOTING section. See the GAS INJECTION TROUBLE SHOOTING article in that section.