Engine Controls - System/component Tests: Other Geo Metro I

TERMINOLOGY

Note. Terms ECM and PCM are used interchangeably in this article.

Due to federal government requirements, manufacturers may use names and acronyms for systems and components different than those used in previous years. SAE TERMINOLOGY table will help eliminate confusion when dealing with these components and systems. Only relevant components and systems whose names have changed from current General Motors Corp. terminology have been listed.

SAE TERMINOLOGY CHART

Ground Circuit Checks

Check ground circuits to ECM for continuity to ground. Using a DVOM, touch negative voltmeter lead to a good ground. Touch positive voltmeter lead to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If volt-meter reading is greater than one volt, check for open, corrosion or loose connection on ground lead. To identify ECM ground terminals, see WIRING DIAGRAMS article in this section.

Power Circuit Checks

Using DVOM, check power circuits to ECM for opens or shorts. To identify ECM power terminals, see WIRING DIAGRAMS article in this section.

COOLANT TEMPERATURE SENSOR

1. Remove coolant temperature sensor. See «COOLANT TEMPERATURE SENSOR LOCATION»(ref-19479-S08774684042001010200000) table.
2. Measure resistance of coolant temperature sensor at designated temperatures. Replace sensor if it is not within specification. See «COOLANT TEMPERATURE SENSOR RESISTANCE»(ref-19479-S10900674612001010200000) table.

COOLANT TEMPERATURE SENSOR LOCATION

COOLANT TEMPERATURE SENSOR RESISTANCE

CRANK ANGLE SENSOR (METRO XFi)

1. Disconnect 2-pin connector at distributor. Using ohmmeter, measure crank angle sensor resistance between terminals on connector at distributor.
2. Resistance should be 140-180 ohms. Replace distributor assembly if resistance is not within specification.
3. With DVOM still connected, use voltmeter to measure AC voltage while cranking engine. Voltage should be .1-.4 volt. If voltage is not within specification, ensure crank angle sensor air gap is .008-.016" (0.2-0.4 mm). If air gap is okay, replace distributor.
4. If voltage was within specification, turn ignition off. Reconnect distributor connector. Disconnect ECM connector C2. Connect voltmeter from ECM connector C2 cavity B1 to cavity B9. If voltage is .1-.4 volt with engine cranking, check for poor connection at ECM. If connection is okay, replace ECM. If voltage is not within .1-.4 volt with engine cranking, check for poor connection at distributor. If connection is good, repair open, short to ground or short to B+ in Light Green or Purple wire to ECM.

EGR TEMPERATURE SENSOR

See EXHAUST GAS RECIRCULATION under EMISSIONS SYSTEMS & SUB-SYSTEMS.

Note. Electrical load sensor may be referred to as diode module.

ELECTRICAL LOAD SENSOR (METRO)

1. Warm engine to normal operating temperature. Turn ignition off. Install tachometer. Start engine and note idle RPM. Individually turn headlights, stoplights, heater blower and rear defogger on and off, noting engine speed with each accessory on. Engine speed should increase when each component is turned on.
2. If engine speed does not increase, go to step 3). If engine speed increases with operation of each accessory, electrical load sensor is okay. Ensure electrical connections at ECM and electrical load sensor are secure. ECM is located under left side of dash. Diode module is located behind instrument panel, near steering column. (Scheme 40)
3. Using voltmeter, backprobe Brown/White wire terminal A2 (M/T) or B12 (A/T) at ECM and ground. ECM is located under left side of dash. Individually turn headlights, stoplights, heater blower and rear defogger on and off. Battery voltage should be indicated when each accessory is turned on.
4. If battery voltage exists, check for loose connections at ECM or defective ECM. If battery voltage does not exist, check for open wiring circuit on appropriate accessory. See «ACCESSORY WIRING COLOR»(ref-19479-S14936009632001010200000) table. If wiring is okay, replace diode module.

ACCESSORY WIRING COLOR

Scheme 40

INTAKE AIR TEMPERATURE (IAT) SENSOR

Note IAT sensor location. See IAT SENSOR LOCATION table. Using ohmmeter, check resistance across IAT sensor terminals. Replace IAT sensor if resistance is not within specification. See IAT SENSOR RESISTANCE SPECIFICATIONS table.

IAT SENSOR LOCATION

IAT SENSOR RESISTANCE SPECIFICATIONS

MAP SENSOR WIRE TERMINAL IDENTIFICATION

PARK/NEUTRAL POSITION SWITCH CONTINUITY

THROTTLE POSITION (TP) SENSOR (METRO)

1. With battery disconnected, remove EVAP hoses, A/C solenoid vacuum valve hose (if equipped), IAT sensor electrical connector and air cleaner from TBI.
2. Using ohmmeter, check continuity between designated terminals. Adjust or replace switch if it is not within specification. (Scheme 41) See «THROTTLE POSITION (TP) SENSOR RESISTANCE»(ref-19479-S14423986242001010200000) table. If resistance is not within specification, adjust/replace TP sensor.

Scheme 41

THROTTLE POSITION (TP) SENSOR RESISTANCE

VEHICLE SPEED SENSOR

To test vehicle speed sensor circuit and identify VSS terminals see scheme 7, see scheme 8 and see scheme 9.

Diode Module

Diode module is also referred to as electrical load sensor. See ELECTRICAL LOAD SENSOR (METRO) under ENGINE SENSORS & SWITCHES under COMPUTERIZED ENGINE CONTROLS.

EFI Main Relay

1. EFI main relay is located in fuse/relay block on left side of engine compartment, near battery. Remove EFI main relay from fuse/relay block.
2. Using ohmmeter, ensure continuity exists between Black/White and Black wire terminals of EFI main relay. Apply battery voltage to Black/White wire terminal. Ground Black wire terminal. Continuity should exist between White/Red and White/Blue wire terminals of EFI main relay. Replace EFI main relay if continuity is not as specified.

Fuel Pump Relay

1. Fuel pump relay is located in fuse/relay box on left side of engine compartment, near battery. Remove fuel pump relay from fuse/relay box.
2. Using an ohmmeter, ensure continuity exists between Black and Pink wire terminals of fuel pump relay. Apply battery voltage to Black wire terminal, and ground Pink wire terminal. Continuity should exist between White/Blue and Purple or Pink wire terminals of fuel pump relay. Replace fuel pump relay if continuity is not as specified.

Idle Speed Control Solenoid

See IDLE CONTROL SYSTEM .

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING article in this section.

Fuel Pressure Regulator Vacuum Switching Valve (Prizm LSi) -Fuel pressure regulator Vacuum Switching Valve (VSV) is located near rear of intake manifold and contains a Black/Red and Light Green wire connector. Other information is not available from manufacturer.

Fuel Injector

Check resistance across fuel injector terminals. Replace fuel injector if resistance is not within specification. See FUEL INJECTOR RESISTANCE SPECIFICATIONS table.

FUEL INJECTOR RESISTANCE SPECIFICATIONS

A/C VACUUM SWITCHING VALVE

1. When A/C is operated, ECM operates A/C Solenoid Vacuum (SV) valve to supply by-pass air to increase engine idle speed. A/C SV valve is mounted on firewall, right of ignition coil. (Scheme 42) Install Tech 1 scan tester. Start and run engine. Turn A/C on and blower speed selector switch to any position except OFF. If engine speed increases slightly with A/C operation, A/C SV valve system is functioning normally.
2. If engine speed does not increase, backprobe A/C SV valve connector from cavity No. 2 to ground using a fused jumper. If engine speed increases, check for an open in Blue/Red wire. If wiring is okay, replace A/C amplifier. If engine speed does not increase, check for an open in Yellow wire. If wiring is okay, replace A/C SV valve.

Scheme 42

AIR VALVE

1. Remove throttle body assembly from intake manifold. Separate upper and lower bodies. Place sensing portion of air valve in water. (Scheme 43)
2. Heat water to 176°F (80°C). Ensure air valve fully closes. Air valve should be open when cool. Replace air valve if it is defective. Reassemble throttle body. Tighten screws to 31 INCH lbs. (3.5 N.m).

Scheme 43

IDLE AIR CONTROL VALVE

1. Idle Air Control (IAC) valve is located below left side of air cleaner. IAC valve by-passes air around throttle valve and directly into intake manifold. Air is allowed to pass through IAC valve when valve is energized by ECM.
2. IAC valve is energized whenever idle speed drops to less than desired RPM due to engine load (i.e., electrical, P/S, A/T in Drive, etc.). IAC valve is energized each time engine is started and during periods of deceleration to compensate for rich mixtures caused by a fully closed throttle. Other information is not available from manufacturer.

IGNITION SYSTEM

Note. For basic ignition checks, see BASIC TESTING article in this section.

Electronic Ignition Timing Advance

Ignition timing is controlled by Electronic Control Module (ECM). Testing information is not supplied by manufacturer. If crank angle sensor fails, a trouble code may be set. See TESTS W/CODES article in this section.

Mechanical Advance (Metro Without ESC)

Remove distributor cap. Turn rotor clockwise. Release rotor and observe movement. Rotor should smoothly return to full rest position. If mechanical advance performance is incorrect, replace distributor.

Vacuum Advance (Metro Without ESC)

1. Remove distributor cap. Disconnect vacuum hoses from vacuum advance unit on distributor. Using vacuum pump, apply 15 in. Hg of vacuum on outer vacuum advance unit while observing advance plate assembly.
2. Advance plate assembly should operate with a smooth movement and vacuum should not bleed off. Repeat procedure on inner vacuum advance unit. If vacuum advance unit does not operate correctly, replace vacuum advance unit.

EGR System Check

1. With engine cool, grasp top of EGR valve and check for looseness. If looseness is felt, replace EGR valve. WARNING: Wear gloves if EGR valve is hot.
2. Warm engine to normal operating temperature. Place finger on bottom of EGR valve diaphragm. Start engine. Increase engine speed. Note if EGR valve diaphragm moves. If diaphragm does not move, allow engine to idle. Disconnect vacuum hose from EGR valve. Apply 10 in. Hg of vacuum to valve. Vacuum should hold and engine should run rough or stall. If vacuum does not hold, go to step 4).
3. If engine ran rough or stalled and EGR valve held vacuum, check components controlling vacuum supply to EGR valve (i.e., EGR modulator, EGR vacuum switching valve, vacuum supply and hoses). Also, check ECM control of ground circuit to EGR vacuum switching valve and verify EGR vacuum switching valve has power when ignition is on. For wire colors and ECM terminal identification, see WIRING DIAGRAMS article in this section.
4. If EGR valve did not hold vacuum, replace EGR valve. If engine did not run rough or stall, remove EGR valve and check for plugged EGR valve or EGR passages in intake/exhaust system. Clean or replace as necessary.

EGR Vacuum Supply

Locate EGR vacuum supply port on throttle body or intake manifold. Disconnect vacuum supply hose. Connect vacuum gauge to port. Start engine. Increase engine speed to 2000 RPM, and note vacuum reading. At least 10 in. Hg of vacuum should be obtained. If vacuum is low, check vacuum supply port for restriction (carbon, dirt, etc.).

EGR Modulator

1. Remove EGR modulator. Plug one upper vacuum hose fitting while blowing air into other upper vacuum hose fitting. Air should pass through filter.
2. Connect vacuum pump to either upper vacuum hose fittings. Plug other upper vacuum hose fitting (exhaust gas pressure port). Blow air into bottom vacuum hose fitting while applying vacuum using vacuum pump. Vacuum should be obtained. Replace modulator if defective.

EGR Vacuum Switching Valve (SV)

1. With ignition off, disconnect vacuum hoses and wiring from solenoid. For SV location, see «EGR VACUUM SWITCHING VALVE LOCATION»(ref-19479-S01053271842001010200000) table. Using ohmmeter, ensure resistance between SV terminals is 33-39 ohms.
2. Blow air into port No. 1, ensuring air flows through filter only. (Scheme 44) Apply battery voltage and ground to SV terminals. With SV energized, blow air into port No. 1 to ensure air flows out port No. 2. Replace SV if defective.
3. Check ECM control of ground circuit to EGR SV. Ensure SV has voltage with ignition on. For wire colors and ECM terminal identification, see WIRING DIAGRAMS article in this section.

EGR VACUUM SWITCHING VALVE LOCATION

Scheme 44

Fuel Evaporation Canister Check Valve

While blowing into charcoal canister tank port, ensure air flows out air port (bottom of canister). (Scheme 45) While blowing air into purge port, air should not pass through air port. Apply 20 in. Hg of vacuum to TB port of canister valve. Blow air into purge port. Air should come out tank port. Replace check valve if defective.

Scheme 45

Fuel Evaporation Bimetallic Vacuum Switching Valve (BVSV)

Remove vacuum hose from BVSV, located on intake manifold. With engine cold, blow into BVSV. Air should pass through valve. With engine temperature greater than 140°F (60°C), blow into valve. Air should not pass. Replace BVSV if defective.

2-Way Check Valve

Remove 2-way check valve, located in line from fuel tank to fuel evaporation canister. Blow air from Black side (fuel tank side) of check valve. Air should pass through check valve with slight resistance. Blow through Orange side (canister side) of check valve. Air should pass easily through check valve. If air passes easily from Black side or does not pass at all in both directions, replace check valve.

PCV Valve

Remove PCV valve from valve cover. Run engine at idle, placing thumb over end of hose to check for vacuum. If vacuum does not exist, check for plugged hoses or manifold port. Turn engine off. Remove PCV valve. Shake valve to ensure needle inside valve is free. Replace valve if needle is not free.

MISCELLANEOUS CONTROLS

Note. Although some controlled devices listed here are not technically engine performance components, they can affect driveability if they malfunction.

A/C CLUTCH SYSTEM CONTROLS

Note. When A/C is operated, ECM will supply a ground to compressor relay. Compressor relay then supplies voltage to A/C clutch.

Shift Indicator Light (Metro M/T)

1. Turn ignition on and note shift indicator light. If shift indicator light is on, go to next step. If shift indicator light is off, go to step 3).
2. Turn ignition off. Disconnect ECM, located under left side of dash. Turn ignition on and note shift indicator light. If shift indicator light is off, ECM is faulty. If shift indicator light is on, check for short to ground in Light Blue wire between ECM and shift indicator light.
3. Turn ignition off. Disconnect electrical connectors at ECM, located under left side of dash. Turn ignition on. Install jumper wire between Light Blue wire of ECM connector and ground.
4. If shift indicator light is on, check for defective connection at ECM or for faulty ECM. If shift indicator light is off, check for defective bulb, open in power supply circuit to shift indicator light and open in Light Blue wire from shift indicator light to ECM.

CODE 24 VEHICLE SPEED SENSOR (VSS) CIRCUIT

ECM supplies 12 volts to VSS. With vehicle moving, reed switch inside VSS will open and close 4 times per revolution of speedometer cable. As reed switch opens and closes, voltage at ECM is toggled high and low. ECM converts this toggled voltage into vehicle speed displayed as MPH or KPH. Code 24 will set if constant voltage (high or low) lasts at least 4 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for intermittents.
2. Checks for VSS not receiving 12 volts from ECM (open in Yellow/Green wire or faulty ECM).
3. Checks for poor ground connection or a faulty VSS.