Engine Controls - Tests W/codes: Other Geo Metro I

MALFUNCTION INDICATOR LIGHT (MIL)

Note. MIL is also known as the CHECK ENGINE light.

All vehicles are equipped with a Malfunction Indicator Light (MIL), located on instrument panel. Light comes on, as a bulb check, when ignition switch is turned to ON position and engine is not running. Light should not flash at this time and should go out when engine is started.

If MIL remains on or flashes with engine running, self-diagnostic system has detected a problem. If problem goes away, light will go out after 10 seconds, but a fault code will be stored in ECM memory.

All trouble codes except Code 41 (ignition signal circuit) are stored in ECM memory. Code 41 is erased from memory as soon as ignition is turned off. In order to detect an active Code 41, connect a scan tester to Data Link Connector (DLC). Crank engine for 3 seconds, and leave ignition switch in ON position. If ignition switch is turned to OFF position, a hard or active Code 41 will be lost.

Hard Failures

Hard failures will cause Malfunction Indicator Light (MIL) to glow and remain on until malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, ECM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but loss of good driveability will most likely occur.

Intermittent Failures

Intermittent failures may cause Malfunction Indicator Light (MIL) to flicker or glow and go out after intermittent fault goes away. However, corresponding fault code will be retained in ECM memory. If fault does not reoccur within a certain time frame, related fault code will be erased from ECM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in this section.

RETRIEVING CODES

1. Perform diagnostic circuit check before diagnosing vehicle using self-diagnostic system. See appropriate DIAGNOSTIC CIRCUIT CHECK chart under «DIAGNOSTIC CODE CHARTS»(ref-19474-S21161794982001010200000).
2. Fault codes can be retrieved using a scan tester connected to Data Link Connector (DLC) or by counting flashes of Malfunction Indicator Light (MIL) after grounding either DIAG SW connector in fuse block or diagnostic request terminal in duty check data link connector, located on left side of firewall. (Scheme 35)
3. To retrieve code(s) using DIAG SW connector in fuse block, remove spare fuse from fuse block and insert into DIAG SW connector terminal. (Scheme 35) Turn ignition on and observe MIL to read fault code(s). Proceed to appropriate chart(s) under DIAGNOSTIC CODE CHARTS to diagnose fault codes.
4. To retrieve code(s) using the duty check data link connector, connect jumper between duty check data link connector terminals No. 2 and 4. (Scheme 35) Turn ignition on and observe MIL to read fault code(s). Proceed to appropriate chart(s) under DIAGNOSTIC CODE CHARTS to diagnose fault codes.
5. If no fault codes are stored, MIL will flash Code 12, indicating ECM diagnostic system is operating. If fault codes are stored, code will flash 3 times, starting with the lowest code. Proceed to appropriate chart(s) under DIAGNOSTIC CODE CHARTS to diagnose fault codes.

Scheme 35

FAULT CODE IDENTIFICATION

CLEARING CODES

Turn ignition switch to OFF position. Remove TAIL fuse in passenger compartment fuse block or 40-amp fusible link (Green) in underhood fuse/relay block (located on left fender panel) for at least 30 seconds. ECM fault code memory is now clear. If 40-amp fusible link is removed to clear ECM memory, clock and radio memory will also be erased.

CHART A-1, NO MALFUNCTION INDICATOR LIGHT (MIL)

Malfunction Indicator Light (MIL) should remain on when ignition switch is in ON position and engine is not running. Battery voltage is applied to indicator bulb. ECM controls indicator bulb and turns it on by providing a ground path through Purple wire to ECM.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks if ECM is receiving power.
2. Checks if ECM is faulty.
3. Checks for open in White/Blue wire between Fuel Injection (FI) relay and ECM.
4. Checks if ECM has a good ground.
5. Checks for open in Black/White wire to instrument panel, and Purple wire to ECM.
6. Checks if Fuel Injection (FI) relay switch is receiving power.
7. Checks if Fuel Injection (FI) relay coil is receiving power.
8. Checks if Fuel Injection (FI) relay or ECM is faulty, or circuit is open in Black wire between Fuel Injection (FI) relay and ground.

CHART A-2, WON'T FLASH CODE 12, OR ANY CODES, MIL ON STEADY

Malfunction Indicator Light (MIL) will flash trouble codes when either diagnostic request terminal in duty check data link connector or DIAG SW connector in fuse block is grounded.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for a grounded light circuit.
2. Checks if problem is an open circuit in diagnostic terminal or a faulty ECM.

Chart A-2 - Flow Chart Won't Flash Code 12 Or Any Codes, MIL On steady. Scheme 36

CODE 13, OXYGEN SENSOR CKT, SIGNAL VOLTAGE DOES NOT CHANGE

Oxygen (O2) sensor produces a varying voltage after exhaust temperature is greater than 600°F (316°C). This voltage varies from 0-.9 volt, depending on exhaust gas oxygen content. After sensor is hot and voltage is more than .45 volt and does not vary, a rich condition is indicated. If voltage is less than .45 volt and does not vary, a lean condition is indicated.

O2 sensor will not produce a voltage until it reaches 600°F (316°C). An open sensor circuit causes fuel control system to operate in an open loop condition.

Note. Test numbers refer to test numbers on diagnostic chart.

1. O2 sensor output voltage should be fluctuating between 0-1 volt.
2. When vacuum hose is disconnected from MAP sensor, MAP sensor output voltage will increase and ECM should interpret this as a high engine load. ECM should increase fuel injector pulse width, causing a rich air/fuel mixture. This should cause O2 sensor to generate a high output voltage (usually, greater than .9 volt).

CODE 14, ECT SENSOR CKT, LOW TEMPERATURE INDICATED

Engine Coolant Temperature (ECT) sensor is a thermistor in series with a fixed resistor in ECM. ECM applies 5 volts to sensor. ECM monitors voltage across ECT sensor and converts it into a temperature reading. When engine is cold, ECT sensor resistance is high. When engine is warm, ECT sensor resistance is low. Therefore, when engine is cold, ECM receives a high voltage input and when engine is warm, ECM receives a low voltage input.

Code 14 will set if the following condition is met for at least 3 seconds

1. Voltage input at ECM indicates a coolant temperature of less than -54°F (-48°C). NOTE: Test numbers refer to test numbers on diagnostic chart.

1. This test simulates Code 15. If ECM stores Code 15, ECM and its wiring is okay and ECT sensor is faulty. If Code 14 resets, ECT sensor is okay and wiring to ECM or ECM is faulty.
2. This test determines whether there is an open in Gray/White or Light Green/Black wire, a short to B+ in Gray/White wire, or a faulty ECM.

CODE 15, ECT SENSOR CIRCUIT, HIGH TEMPERATURE INDICATED

Engine Coolant Temperature (ECT) sensor is a thermistor in series with a fixed resistor in ECM. ECM applies 5 volts to sensor. ECM monitors voltage across ECT sensor and converts it into a temperature reading. When engine is cold, ECT sensor resistance is high. When engine is warm, ECT sensor resistance is low. Therefore, when engine is cold, ECM receives a high voltage input and when engine is warm, ECM receives a low voltage input.

Code 15 will set if voltage input at ECM indicates a coolant temperature of greater than 276°F (136°C) for at least 3 seconds.

Note. Test number refers to number on diagnostic chart.

1. This test simulates Code 14. If ECM sets Code 14, ECM and its wiring are okay and ECT sensor is faulty. If Code 15 resets, ECT sensor is okay and wiring to ECM or ECM is faulty.

CODE 21, TP SENSOR CKT, SIGNAL VOLTAGE HIGH

Throttle Position (TP) sensor resistance changes along with throttle valve position. ECM provides a 5-volt reference voltage to TP sensor. ECM reads voltage across sensor and converts it into a throttle position. When TP sensor resistance decreases, indicating throttle valve opening is increasing to WOT, voltage being monitored at ECM increases. When sensor resistance increases, indicating throttle valve opening is decreasing to idle, voltage being monitored at ECM decreases.

Code 21 will set when high voltage input at ECM was indicated for 2 seconds with engine running at idle.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for open or short to B+ in Light Green/White wire or a faulty ECM.
2. Checks for open or short to B+ in Light Green wire or a faulty ECM.
3. Checks for a faulty ECM, or a misadjusted or faulty TP sensor.

CODE 22, TP SENSOR CIRCUIT, SIGNAL VOLTAGE LOW

Throttle Position (TP) sensor resistance changes along with throttle valve position. ECM provides a 5-volt reference voltage to TP sensor. ECM reads voltage across sensor and converts it into a throttle position. When TP sensor resistance decreases, indicating throttle valve opening is increasing to WOT, voltage being monitored at ECM increases. When sensor resistance increases, indicating throttle valve opening is decreasing to idle, voltage being monitored at ECM decreases.

Code 22 will set when low voltage input at ECM was indicated for 2 seconds with engine running off idle.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Measures TP sensor signal voltage at sensor. Checks for short to ground in Light Green/White wire.
2. Checks for reference voltage from ECM.

CODE 23, IAT SENSOR CIRCUIT, LOW TEMPERATURE INDICATE

Intake Air Temperature (IAT) sensor uses a thermistor in series with a fixed resistor inside ECM to control signal voltage to ECM. ECM applies 5 volts to IAT sensor. ECM monitors voltage across IAT sensor and converts it into temperature reading. When outside temperature is cold, IAT resistance is high. When outside temperature is warm, IAT resistance is low. Therefore, when air temperature is cold, ECM will receive a high voltage input. When air temperature is warm, ECM will receive a low voltage input. Code 23 will set if voltage input at ECM indicates for 3 seconds that air temperature is less than -54°F (-48°C).

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test simulates Code 25. If ECM stores Code 25, ECM and its wiring are okay and IAT sensor is faulty. If Code 23 resets, IAT sensor is okay and wiring to ECM or ECM is faulty.
2. Checks for open in Gray or Light Green/Black wire, a short to B+ in Gray wire or a faulty ECM.

CODE 24, VEHICLE SPEED SENSOR CIRCUIT

ECM supplies a B+ signal to Vehicle Speed Sensor (VSS). While vehicle is moving, a reed switch inside VSS will open and close, toggling B+ signal high and low. ECM then converts this toggled high/low voltage into a vehicle speed that is displayed as MPH/KPH.

Code 24 will set if a constant voltage signal (high or low) is not detected at ECM for at least 4 seconds, with engine running and vehicle moving.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks if problem is intermittent.
2. If VSS is not receiving 12 volts from ECM, Code 24 will set. Checks for open in Yellow/Green wire or a faulty ECM.
3. Checks for a poor ground connection, an open in Black/Blue wire or a faulty VSS.

CODE 25, IAT SENSOR CIRCUIT, HIGH TEMPERATURE INDICATED

Intake Air Temperature (IAT) sensor uses a thermistor in series with a fixed resistor inside ECM to control signal voltage to ECM. ECM applies 5 volts to IAT sensor. ECM monitors voltage across IAT sensor and converts it into temperature reading. When outside temperature is cold, IAT resistance is high. When outside temperature is warm, IAT resistance is low. Therefore, when air temperature is cold, ECM will receive a high voltage input. When air temperature is warm, ECM will receive a low voltage input.

Code 25 will set if voltage input at ECM indicates an air temperature of greater than 277°F (136°C) for at least 3 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test simulates Code 23. If ECM stores Code 23, ECM and its wiring are okay and IAT sensor is faulty. If Code 25 resets, IAT sensor is okay and wiring to ECM or ECM is faulty.

CODE 31, MAP SENSOR CIRCUIT, LOW VOLTAGE INPUT - LOW VACUUM

MAP sensor responds to changes in manifold pressure (vacuum). ECM applies 5 volts to MAP sensor. Changes in pressure, engine load and RPM are converted into voltage input monitored by ECM. A low voltage reading at ECM indicates low manifold pressure and a high voltage at ECM indicates high manifold pressure.

Code 31 will set when high voltage input at ECM indicates intake manifold pressure greater than 840 mm Hg. of vacuum for at least .2 second.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks if ECM is providing a 5 volt reference.
2. Checks for bias voltage to MAP sensor which has a value between 4.5 and 4.9 volts.

CODE 32, MAP SENSOR CIRCUIT, HIGH VOLTAGE INPUT - HIGH VACUUM

MAP sensor responds to changes in manifold pressure (vacuum). ECM applies 5 volts to MAP sensor. Changes in pressure, engine load and RPM are converted into voltage input monitored by ECM. A low voltage reading at ECM indicates low manifold pressure and a high voltage at ECM indicates high manifold pressure.

Code 32 will set when low voltage input at ECM indicates intake manifold pressure less than 40 mm Hg. of vacuum for at least .2 second.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for open or short to voltage in Light Green/Red wire or a faulty ECM. Under normal conditions Light Green/Red wire should have an available voltage of less than 5 volts. A short to 5 volts or B+ will set Code 32.
2. Checks for open in Light Green/Black wire, poor connection at MAP sensor or ECM, or a faulty MAP sensor or ECM.

CODE 41, IGNITION SIGNAL CIRCUIT, NO SIGNAL

ECM receives ignition signal when ignition switch is turned to ON position. When ignition is in START position, this signal is toggled on and off through ECM. As this signal is toggled on and off, it induces a voltage in secondary coil of ignition coil. This induced voltage is then used to fire spark plugs.

Code 41 will set if toggled ignition signal is not present at ECM within 3 seconds of cranking.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for power at ignition coil.
2. Checks for poor connection or a faulty ignition coil.
3. Checks for poor connection or a faulty ECM.
4. Checks for faulty noise suppressor filter.
5. Checks for open or short circuit to ground in wires between ignition coil, noise suppressor filter and ECM.

CODE 42, CAMSHAFT POSITION SENS CKT, NO SIGNAL FOR 2 SECONDS

When distributor shaft rotates, a fluctuating magnetic field is generated due to changes in air gap between Camshaft Position (CMP) sensor and distributor shaft signal rotor. As a result, a small AC voltage is induced in CMP sensor. This ignition reference signal is sent to ECM on ECM terminals B1 and B9. ECM monitors AC voltage between these terminals. ECM uses this signal in determining when to fire ignition coil and fuel injector.

Code 42 will set when ignition signal is not present at ECM for 2 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks Camshaft Position (CMP) sensor resistance.
2. Checks for a proper AC signal voltage being produced. When distributor shaft turns, CMP sensor acts as an AC voltage signal generator.
3. Checks if proper AC signal voltage is getting through to ECM connector.

CODE 51, EXHAUST GAS RECIRCULATION (EGR) CIRCUIT

EGR Vacuum Switching Valve (VSV) solenoid is controlled by ECM. VSV solenoid is supplied with battery voltage through Fuel Injector (FI) relay. ECM completes ground circuit to energize VSV solenoid.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks circuit for a short to ground.
2. Checks for voltage from Fuel Injection (FI) relay.
3. Checks circuit for a short to ground or a faulty ECM.
4. Checks for open in VSV circuit (Green wire).
5. High resistance in solenoid can set Code 51.

SUMMARY

If no hard fault codes are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.